So we did this half-tato diet community trial. People signed up for a minimum of six weeks — two weeks of baseline, so we could see how their weight changed when they were eating as normal, and then four weeks where they got around 50% of their calories from potatoes every day.

This was inspired by our original Potato Diet Community Trial, which worked pretty well. In that study, people lost an average of 10.6 lbs over four weeks eating almost nothing but potatoes.

We say “almost nothing but potatoes” because most people took multiple cheat days, and it didn’t seem to make much of a difference. Combined with a couple of case studies, who reported enormous success on a half-tato diet (in particular, M with his potatoes-by-default), this made us wonder if a half-tato diet could be made to work almost as well as a full-tato diet. 

Anyways, let’s look at some results. 

Today’s analysis is based on a snapshot of the data taken on June 1, 2023 (about 10 weeks after the study was launched). This means we have up to 10 weeks of data, specifically 2 weeks of baseline and 8 weeks of half-tato. A few people are still going with the half-tato diet, but we will look at their data later.

The dataset is mostly straightforward, but here’s one note: One or two important measurements were missing for a small number of people. For example, they might have entered a weight for Day 28 and Day 30, but not Day 29 (which is important because Day 29 is the end of the first four weeks). 

When an important measurement like this was found to be missing, we filled it in by making the missing measurement the average of the two values around it. For example, if the weight measurement for Day 29 was missing, we filled it in with the average of the weights on Day 28 and Day 30.

We did all these replacements before doing the analysis, and only a few measurements were interpolated like this.

As usual: raw data, the analysis script, and study materials are available on the OSF. 

Participants

A total of 123 people filled out the signup form. 

Of those, 8 people filled out the form incorrectly in such a way that we couldn’t sign them up (they didn’t enter an email, didn’t enter critical data such as height, etc.). We enrolled the remaining 115 people in the study.

Of the 115 people who were enrolled, 92 entered at least one day of weight data.

For people who entered any data, the most common outcome was to make it the full 2 weeks baseline + 4 weeks half-tato, though people dropped out at various points along the way, and a few people didn’t finish the baseline two weeks. 

Here you can see how many days people completed. In this figure, the vertical line at 0 divides the baseline span (Days -14 to -1) from the half-tato span of up to 8 weeks (Days 1 to 57). 

Let’s summarize that plot. As of the snapshot on June 1st:

• 92 people entered at least one day of weight data
• 75 people made it to Day 1, past the baseline period of two weeks
• 38 people made it to Day 29, the end of the first 4 weeks of half-tato
• 8 people made it to 8 weeks or further, and some are still going

For this analysis, we will mostly be focusing on weight change up to Day 29, since there’s not much data past that point. 

Weight Change over Baseline

First let’s look at the baseline. Similar to a crossover design, this baseline serves as a kind of control group.

There was very little average weight change in the baseline period, and it was not statistically distinguishable from zero. Here’s the histogram of weight change over baseline, with a black vertical line at 0 lbs (i.e. no weight change over baseline) and a red dashed vertical line at the mean weight change:

The mean weight change over this period was -0.22 lbs, with a 95% CI of -0.70 lbs to 0.27 lbs. This is not statistically distinct from zero. 

The mean suggests an average loss of 0.11 lbs per week on average, or 0.35 per week if we take the lower bound of the confidence interval. 

Of course, it’s also consistent with an average weight GAIN of 0.14 lbs per week if we take the upper bound of the confidence interval.

In previous studies, people have expressed concern about the Hawthorne effect — that when we ask people to measure their weight, they might start losing weight simply because they are aware that their weight is being observed. Looking at the baseline period, we find very little support for this idea, even with a sample size of 75 people. 

Observing your weight for two weeks just doesn’t change it much, and likely doesn’t change it at all. Going forward, we will continue to not worry about the so-called Hawthorne effect. 

(Also, it’s amusing to see that Wikipedia kind of drags this whole idea: “some scholars feel the descriptions are fictitious” and “J. G. Adair warned of gross factual inaccuracy in most secondary publications on the Hawthorne effect and that many studies failed to find it.”)

Here’s a plot of weight change over baseline, including only people who finished the two-week span. As you can see, these look like a bunch of random walks around zero.  

Weight Change at Four Weeks

Our main interest is weight change on the half-tato diet, specifically people’s weight change between the morning of Day 1 and the morning of Day 29. Here’s the histogram of that variable, with a black vertical line at 0 lbs (i.e. no weight change over 29 days) and a red dashed vertical line at the mean weight change:

People lost 1.7 lbs on average over these four weeks, and that loss is significantly different from zero, t(37) = 2.70, p = .010. Another way of putting this is that 27 out of 38 people (71%) lost at least some weight.

By now we’re sure you’ve noticed the extreme outlier, the person who reported losing 17 lbs over four weeks (participant 25348806). This outlier is impressive, and we’ll look at her results in more detail later, but excluding that person doesn’t change the overall results. Without the outlier, average weight loss is 1.3 lbs over four weeks, and that loss remains significantly different from zero, t(36) = 2.66, p = .012.  

We see that weight loss is significantly different from zero. People do seem to lose weight on the half-tato diet. 

But we should also emphasize that they don’t lose much — the effect size here is a disappointment. We had hoped that the half-tato diet might have around half the effect of the full potato diet, but that just didn’t happen. 

Overall, the effect is less than half the effect of the original potato diet. Average weight loss on the potato diet was 10.6 lbs, so half of that would be 5.3 lbs. Instead we see only around 15% of the effect of the full-tato diet. 

We should note that there are some mitigating factors here. In particular, about 30% of participants in the half-tato diet started out as “normal weight” (BMI < 25), compared to only about 15% in the original potato diet. (In the original study, people who were obese or overweight tended to lose more weight, so this means the average weight loss will look smaller when there are fewer obese or overweight participants.)

But weight loss on half-tato is still quite minor, even if you limit the analysis just to overweight (BMI > 25) participants, who lost 1.8 lbs on average, or obese (BMI > 30) participants, who lost 3.1 lbs on average. This is still much less weight loss than on the original potato diet.

Another way to put it is like so: On the original potato diet, 64 people made it 4 weeks. One of those people lost no weight. Everyone else lost more than the AVERAGE weight loss on the half-tato diet. It’s really no contest; full-tato is overwhelmingly more reliable and causes overwhelmingly more weight loss, at least among the people who can make it four weeks on mostly potatoes. 

Frankly, this just emphasizes how successful the original potato diet study was. In fact, on reflection the Potato Diet Community Trial was probably the most successful weight loss study of all time. Are there any other studies that caused weight loss in 98% of people who finished the study, and caused an average of 10.6 lbs of weight loss over just four weeks? Not that we know of. 

Trajectory

As we mentioned, there’s one extreme outlier who lost 17 lbs over four weeks. You may also have noticed a less-extreme outlier who lost 9 lbs, who happens to be someone who participated in the original Potato Diet Community Trial and saw a lot of weight loss there as well, losing 19 lbs. Both of them stand out quite clearly in a plot of people’s weight loss trajectories:

Having seen some reports like this one, we wondered if there might be a yo-yo effect on the half-tato diet, where in the beginning people lose weight no problem, but at some point the potato effect stops working and their weight heads back to baseline. That seems like a reasonable way to interpret this plot: 

But overall, this doesn’t seem to be the case. In general, half-tato weight loss over four weeks seems small but constant: 

Weight Change at Eight Weeks

We also have a tiny bit of data on people’s weight loss taking the half-tato diet out to eight weeks. Here’s the plot: 

The average weight loss at eight weeks is 3.6 lbs, though you can see that one person has lost more than 10 lbs. With only eight individuals, this is too few people to do a statistical analysis. But it does suggest that longer spans on the half-tato diet may be effective.

Note that the extreme outlier does not appear in this group — that person only sent us data up to Day 29.

Here’s the whole span from everyone who finished baseline (minus our main outlier), showing all data points from the start of baseline to the end of eight weeks: 

What Things Correlate with Weight Loss

There’s not much variation in people’s weight loss over these four weeks, but some people did lose more weight than others. This makes us wonder if there are any variables that might be correlated with weight loss.

Take the analyses below with a grain of salt. They’re very exploratory. The sample size is small. We’re not correcting for multiple comparisons. And of course, all these correlations are correlational.

As you well know, correlation does not imply causation — but as XKCD reminds us, “it does waggle its eyebrows suggestively and gesture furtively while mouthing ‘look over there’.” Correlations can still be suggestive, and if any of the correlations we find are real, we should eventually be able to demonstrate the same relationships experimentally. So let’s take a look and see if anything stands out.

BMI

Our first surprise is that BMI doesn’t seem to have much to do with weight loss.

The correlation between weight loss and starting BMI is relatively small, and is not statistically significant, r(36) = -0.29, p = .078.

Protocol

We let people sign up for three different protocols for the half-tato diet, three different ways you could try to get about 50% of your calories from potatoes. People ended up about evenly split between the three approaches:

Here is a plot of weight loss by each of the protocols:

As you can see, there are no huge differences in weight loss between the three protocols, though Potatoes-By-Default includes the outlier who lost the most weight.

Percent Potato

We asked people to estimate what percent of their total calories they were getting from potatoes each day, and some people reported getting a much higher percent potato than others. Since some people were doing about 50% potato, and others were doing only about 10%, you might suspect that the diet caused more weight loss for people getting more potato. 

This is much more muddy than we expected. Getting closer to 50% of your calories from potatoes does seem to maybe cause more weight loss, but if so, it’s not super clear. The correlation is quite small and not significant, r(36) = -0.28, p = .084, and weaker if you exclude the major outlier, r(35) = -0.24, p = 0.147.

It’s hard to imagine that percent potato doesn’t matter at all, and we do see that the three people who lost the most weight were all getting close to 50% potato. This suggests that for best results, you should try to get around 50% potato on average. But there isn’t a clear correlation overall. 

Dairy

In the original Potato Diet Community Trial, we asked people to avoid dairy entirely. This time around, we decided to just ask people to track how many servings of dairy they got each day. This lets us look for any correlation between dairy consumption and weight loss on half-tato. 

There may be a bit of a trend where more dairy is related to less weight loss, but the person who lost the most weight ate plenty of dairy, and the overall correlation is not significant, r(36) = 0.15, p = .355.

That said, the relationship is slightly stronger if we exclude the outlier, though still not significant, r(35) = 0.29, p = .078.

Tomato 

We were also concerned that tomato products might interfere with potato-based weight loss. So just like dairy, we asked people to track how many servings of tomato products they had each day. Here’s the scatterplot:  

Surprisingly, this relationship is significant, even with such a small sample. The overall correlation is r(36) = 0.37, p = .021, and it remains significant if you remove the extreme outlier, r(35) = 0.36, p = .031. 

You can see that the two outliers, people who lost the most weight, almost entirely avoided tomato products on the diet. Also interesting is that the person who gained the most on the diet happens to be the person who ate the most servings of tomato products. 

This is correlational, not corrected for multiple comparisons, etc., but it does provide more support for our suspicion that tomatoes interfere with the potato weight loss effect. This would be great to experimentally confirm at some point, and it should be relatively easy to test — just assign some people on a potato diet to use ketchup, and others to eat their potatoes bareback, i.e. no ketchup. In the meantime if you are trying to lose weight using potatoes, we certainly encourage you to avoid ketchup.

Cooking Method

We’ve previously mentioned that boiling or soaking potatoes removes a lot of their potassium. So we’re curious to see if people who boiled their potatoes lost less weight than people who baked, roasted, fried, or otherwise kept their potatoes for the most part whole and un-leached. 

Most people didn’t leave detailed notes on how they prepared their taters, but the people who did leave notes often mentioned either boiling them or using frozen potato products, which are generally pre-boiled / blanched / parboiled. 

This might explain why the half-tato diet did not cause much weight loss on average — if we’re right, and the weight loss is caused by potassium (or anything else in the potatoes that is leached out on boiling/blanching/soaking; who knows, maybe iodine), then many people were consuming less effective potatoes.

There aren’t enough reports to bother hand-coding preparation method or doing an analysis, but here are some examples:

(42475044) Most of my potato meals were a 50/50 mix of roasted yellow potatoes (partially peel 1 inch cubes, lightly oil, 375 convection for 45 minutes), and store-bought frozen french fries (whatever seemed to have the least oil) cooked in the air fryer with no additional oil. 

(63062664) My protocol was mostly whole boiled potatoes pan-fried in ~15g of butter or a small glug of rapeseed or olive oil. Usually ~1kg for breakfast + lunch.

(78152385) I ate mainly russet or golden potatoes, baked or roasted, and I didn’t eat the skins of the russet because last time I did that it gave me the worst stomach cramps I’ve ever had. I also ate a lot of Alexia french fries with sea salt, and some sweet potatoes.

(80975703) I always ate potatoes I had boiled in batches and kept in the fridge. My favourites were red potatoes, half peeled, but I also had yellow or white potatoes, fully peeled. Always with a bit of olive oil and salt and spices, chopped up and reheated in a pan on the stove.

(28228309) I had visions of making home-made latkes or really fine hash browns. I just didn’t make time. While I know we are supposed to start with whole potatoes, I’m sure glad I found frozen potato patties at the store, or there’s no way I could’ve even approximated the quantity of potato I needed. I put my toaster to 6 (nearly the highest setting) and toast them twice, and they’re great, and I could do it for breakfast on work days.

(30834698) I do not like skin on the potatoes; I can eat it, but I do not like the taste or how it makes me feel; I prefer them without skin, so I mostly eat them like that; usually just boiled with a pinch of salt, sometimes in the oven, sometimes with a drop of olive oil; sometimes with some harissa; the easiest and tastiest for me was boiled with salt, then peel the skin and eat them

(72618178) In general I was making homemade oven-baked ‘fries’ (thinly sliced par-boiled potato). I would often give in and allow myself ketchup or spicy mayo. I also went through some phases of doing homemade gnocchi, mashed potato, and faux-dauphinoise (thinly sliced, stacked, oven-baked potatoes with veg stock and a bit of butter).

As you can see, many people boiled their potatoes or used frozen potato products that were likely boiled in some way before freezing. But to be fair, this does not describe everyone. Some people did report mostly baking or roasting:

(58681391) I usually baked an entire 5 lb. bag of gold potatoes at 350 for 1.5 hours, for roughly three servings. I didn’t use oil when baking but would sometimes refry the baked potatoes into hash browns with about 1 tsp of avocado oil.

(70030447) My main method for eating potatoes, as I work from home, was to chuck a few russets in the oven for an hour after coating them in salt and pepper, then once they’re done I would cut them into two halves and eat those entirely. I found olive oil a hassle, and putting salt and pepper on the insides after they’re done was also too much hassle for me to want to bother doing everyday. Maybe I’d do that if I cooked them some other way.

Despite eating baked or roasted potatoes, neither of these people lost weight. The first saw no change at all, and the second gained 4 lbs. This is enough to show that baking or roasting is not enough to ensure weight loss. 

But there may be other reasons these two didn’t lose any weight. 58681391 ate a lot of tomato and dairy, and got only about 38% of their calories from potatoes. 70030447 ate an unusually large amount of dairy (third most out of everyone) and got only about 20% calories from potatoes.

In any case, we still suspect that starting with whole, raw potatoes, and not boiling, soaking, or blanching them, might be important for causing potato weight loss. We didn’t make people roast or bake their potatoes in the original potato diet study, but maybe with +90% potato, it doesn’t matter.

It might have been an oversight not to ask people to roast or bake their potatoes for the half-tato protocol. If you’re trying it for yourself, probably don’t boil them or live off of frozen french fries.

Regression Analysis

To wrap up these correlational analyses, we fit some regression models to try to predict weight change from multiple factors at once. In all these models, we excluded the outlier who lost 17 lbs, participant ​​25348806, because we wanted to try to understand things that might have impacted weight change for the average participant, who did not lose so much weight. 

One especially strong model included total dairy consumption (p = .007), total tomato consumption (p = .003), and their interaction (dairy * tomato; p = .035). This interaction had a negative sign, suggesting that tomatoes and dairy are slightly less than the sum of their effects. All three terms were significant predictors of weight change, and the model explained 23.7% of the adjusted variance in people’s weight change. 

This was a much better fit than we expected, especially given the small sample size, and it provides more support for the idea that tomato and dairy consumption for some reason inhibit the potato weight loss effect. Note that this is TOTAL dairy and tomato consumption over four weeks, not average daily consumption, which provided a weaker fit.

This was not the best model we found, however. When you dummy-code the three potato protocols, and put them in a model with total tomato consumption and the two-way interactions, many terms are significant (for example, True Half-Tato condition * tomato sum is significant, p = .0004) and the model explains 37% of the variance in weight loss. We literally are not sure what to think of that, and are not sure how to interpret this result.

In any case, these are very simple models. It will be hard to squeeze more information out of just 37 observations, but if you have experience with more complex forms of statistical modeling, we encourage you to download the data and see if you can make more sense of it than we can. 

Potatosis

Some people liked getting half of their daily calories from potatoes:

(23555212) This was cool! I have a newfound appreciation for potatoes.

Other people did not:

(28228309) Oh happy day. No more forcing myself to eat bland potatoes. 

(81471891) Not super happy with my mindset about this diet. It’s currently “I *have* to eat 1 kg of potatoes per day!”, and feels a bit forced.

This is kind of striking compared to the absolutely rave reviews we got about the 100% potato diet, where most people said that they loved it. You’d think that eating 100% potatoes would be a bigger ask and a bigger pain than eating just 50% potatoes, but apparently not. 

This makes us wonder if most people in this study never went into “potato mode”. In the original potato diet study, we found that after a day or two of eating potatoes, most people’s appetites waned, they didn’t want anything aside from potatoes, and they began to steadily lose weight. This seemed like a separate “mode” the body can be in, that both caused weight loss and made it easy to eat nothing but potatoes without major discomfort.

If something about the half-tato diet keeps people from going potato mode — the percent potato wasn’t high enough, the potatoes were prepared wrong, ketchup is a potato inhibitor, etc. — that would explain why people didn’t lose much weight, and why many people found it difficult to stick with even a mere 50% potatoes. 

This is corroborated by a comment from one person who was also a participant in the original potato diet study, and says that they found half-tato very different:  

(42475044) Overall this didn’t work anywhere near as well for me as the full potato. My weight over the last 8 weeks has largely stayed the same, whereas on the full-tato I lost 9 pounds in 3 weeks. I could definitely feel that the potatoes were helping me not gain weight, but I think my non-potato calorie intake was just too high for the potatoes to compensate for. On the full-tato diet I was able to eat as much as I wanted and still lose weight, but that doesn’t seem feasible for me on half-tato.

That said, at least one person on the half-tato diet did report signs that sound a lot like potato mode:

(21268204) Sweating at night, which I never do otherwise. Appetite low… Get full really fast even when eating non-potatoes … 2nd day in a row that it didn’t occur to me to eat until 4pm … Have not been hungry at all the last few days. The calories I did get were because I forced myself to sit down, mostly, with some potatoes

This participant lost only one pound over the first four weeks, but kept going and lost 3.5 lbs over eight weeks. 

All this suggests that there might be a right and a wrong way to do half-tato. If you do it wrong, basically nothing happens, maybe you lose a little weight on average. But if you do it right, you go into potato mode, much like on the full-tato diet, and you start losing weight very quickly.

Let’s assume for the moment that there is such a secret magic switch (or set of switches) that can make half-tato cause rapid weight loss, and try to figure out what it is. If there is such a switch, then almost everyone on the full potato diet tripped it. All the case studies (like M) managed to trip it. The major weight-loss outlier in this study, and maybe some of the less major outliers, seem to have tripped it. Maybe they were doing something right that puts you in potato mode — so what would that be?

The extreme outlier (​​25348806) in this study give us a fairly detailed report of how she approached half-tato, saying:

I signed up for a spreadsheet for 52 weeks.  I’m doing the diet and have had great success … Am female with 100 or so lbs to lose (now 30 down).

I first lost about 15 lbs doing a very loose version of potato by default after first reading your blog pre half tato experiment and have since lost another 15 beginning April 22 with starting half tato in earnest.  I steam peeled yukon gold in batches in the Instant pot for 12-15 minutes at high/manual (depends on size, I try to get bigger but often its just medium available).  Right out of the instant pot I add white vinegar which helps preserve color and appearance and tastes great later (more subtle than adding vinegar at mealtime) before cooling and fridge.  I started eating a mix of cold and hot depending on if microwave is available (sometimes with mustard) but now I’ve settled into just hot (2 min microwave) with mainly salt.  I try to have this 2-3 meals out of the day (2 medium or 1 big 1 smallish per meal).  One of the 2 potato meals I may add one of:  poached egg yolks; calf liver lightly sauted in butter (plus lingonberries and/or honey); or cooked ground beef (with 21 gun salute seasoning from trader joes and sometimes full fat sour cream), and possibly pepper or cholula sauce (rare), occasional oysters (fresh or canned).  I don’t add ketchup (except once – when I went out and had beef fat fries at a steakhouse bar which did not seem to stall).  I really enjoy the potatoes and look forward to them.  I am not hungry but feel satisfied.  I also have dairy – at least one glass of milk a day (either raw whole milk or 2% or whole conventional) – and a small amount of juice or lemonade.  Some mornings I may have full fat yogurt with collagen and stearic acid (see fireinabottle.net) but not all mornings.  I have some extra potassium as well as other supplements.

We love the level of detail, but it’s hard to know which of these elements are required to enter potato mode, if any of them are. But there are some features that this outlier and all the half-tato case studies (M, Nicky, and Joey “No Floors” Freshwater) share:

• Nicky had a bit of ketchup, but everyone else either never or almost never had ketchup with their potatoes. 
• None of them avoided dairy
• All of them mention eating meat and eggs
• All of them used butter and/or oil
• None of them ate boiled potatoes; their potatoes were generally steamed, air fried, microwaved, or baked 

To us, this further supports the idea that at least part of the secret switch is eating not-boiled whole potatoes and mostly avoiding ketchup and tomato products. Dairy doesn’t seem to matter much, or at least it didn’t stop these people, and neither do various fats, meat, or eggs. Of course, it’s difficult to tell if there might be some ADDITIONAL element that they are all getting right. Are they all getting lots of magnesium or something? Hard to say. 

Just in case it helps, here’s a closer look at the other people who lost relatively large amounts of weight on the half-tato diet: 

Participant 26130773 lost the second-most over four weeks on half-tato, a total of 9 lbs. Overall he ate a good potato percentage, reporting 40%-60% most days, though on some days he only got 20%. 

This participant left almost no notes and didn’t report his dairy or tomato intake, which makes it hard to figure out what he might have been doing right. But one thing that jumps out is that it’s clear he was eating lots of eggs. Here are his notes from the first three days of the diet:

5 eggs, potatoes for lunch (350 cal eggs. If I do 2 yokes 3 whites, 190 cal) Protein shake (120) for snack Turkey b patty, salad (600?) 

5 eggs w 2 yolks, few bites turkey (225) Protein shake (120) Soup w meatballs (500) 

5 eggs w 2 yolks (190) Protein shake (120) Normal dinner cheat (900) 2 drinks

Participant 56896462 lost the third-most over four weeks on half-tato, a total of 6 lbs. He had a very good potato percentage, 40% or 50% almost every day. He ate some dairy and some tomato, about 2 servings of dairy a day and 1 of tomato, on average. He also left very few notes, though we notice that he is in Italy.

Conclusions

The half-tato diet causes some weight loss in most people, but for most people, it is much less than half as effective as the full potato diet. If you really want to lose weight, probably go for the full potato diet instead, and try to get as close to 100% of your calories from potatoes as you can.

However, a small number of people do lose a lot of weight on the half-tato diet. This suggests that there might be some way to go into “potato mode” while on half-tato, if you do it right. If we could find out how to make this happen reliably, that would be pretty neat.

Our guess is that it involves some combination of:

• Baking, steaming, microwaving, or roasting whole potatoes instead of boiling them or using pre-boiled frozen potato products
• Avoiding tomato products, especially ketchup
• Getting enough of something else, possibly something found in eggs, meat, or dairy.

We should note that this list is largely based on circumstantial and/or correlational evidence. We do worry that ketchup might be a potato-blocker, but the evidence is not yet all that strong. That makes all of these guesses good subjects for future experiments.

You could design a large trial to answer these questions — randomly assign 100 people to do half-tato with ketchup and 100 people to do half-tato without — but you might need a very large sample size to be able to detect a difference. And while we’d love to see more community trials, it may not be practical to do multiple trials of several hundred people each, one after the other, to try to chase down whether each of these things makes a difference. That seems like it would take forever and be a lot of work.

So instead, another option would be for individuals to test these guesses as a self-experiment, which could provide very strong evidence, and might be able to provide it quickly. 

For example, let’s say that Gary is a fellow who is happily losing 2 lbs a week on the full-tato or half-tato diet. Whatever makes potato mode happen, Gary has found it, even if he doesn’t know what he’s doing right.

Now Gary can test individual switches to see if they turn potato mode off. For example, he can randomly assign some weeks to be ketchup weeks, where he always has ketchup with his potatoes, and other weeks to be no-ketchup weeks, where he religiously avoids ketchup and all other tomato-based foods. 

If Gary’s weight loss always stalls on ketchup weeks, but continues humming along on no-ketchup weeks, that’s a pretty clear sign that avoiding ketchup is one of the switches to make the half-tato diet work. If the randomization makes no difference, that’s a pretty clear sign that ketchup doesn’t matter, at least not for him.

You can imagine a similar design for anything else. Gary could randomly assign some weeks to try only boiled potatoes, and other weeks to try only baked potatoes, and see if it makes any difference. 

We doubt things will be this simple — it’s quite possible that one brand of ketchup kills the potato effect, while another brand has no impact — but we won’t know until someone has tried. It might take several weeks to pick up a clear signal, but anyone who is able to get a potato diet working for them can test any of these switches out for themselves. 

All we ask is that if you try something like this, please publish your results online, regardless of how it turns out. We’re very curious to know what will happen!

Closing Notes

Some people have gone for more than eight weeks on half-tato, and we plan to analyze their results at some point in the future. It will be a small sample size, but we are excited to have some more case studies. So stay tuned. 

If you are interested in doing an N=1 experiment about these ideas and want our help designing a protocol, please feel free to contact us. 

If you would like to be notified of future stupid studies, or if you want to keep up with our work in general, you can subscribe to the blog by email (below), or follow us on twitter.

And if you feel like reading this post has added a couple of dollars’ worth of value to your life, or if you have lost weight as the result of our research and you think it improves the quality of your life by more than one dollar a month, consider donating $1 a month on Patreon. 

Thanks for going on this journey with us.

Sincerely, 
Your friendly neighborhood mad scientists,
SLIME MOLD TIME MOLD

In the original potato diet study, we asked people to try to eat nothing but potatoes. This worked pretty well — people lost 10.6 lbs on average over just four weeks.

But we also told them, “perfect adherence isn’t necessary. If you can’t get potatoes, eat something else rather than go hungry, and pick up the potatoes again when you can.” 

People took this to heart. We asked people to track how often they broke the diet, and almost everyone took at least one cheat day.

Five people said they stuck to the diet 100%, but everyone else said they broke the diet at least once. Most people cheated only a few times, but as you can see from this histogram, a substantial minority cheated more than half the time:

Taking these cheat days didn’t seem to matter much. Almost everyone lost weight, even if they cheated a lot:

In general, the more often people cheated, the less weight they lost. But even the people who cheated the most still lost around 5 lbs. 

Realistically, our original potato diet study was really more like a 90% potato diet. People took quite a few cheat days, and it mostly didn’t seem to matter. Makes you wonder how low we can push that percent and still have it work — after all, the original weight loss effect was ginormous.

This is one reason why today we are announcing a 50% potato diet study. We’re looking for people to volunteer to get about 50% of their calories per day from potatoes for at least four weeks, and to share their data so we can do an analysis. You can sign up below.

Case Studies

The other reason we’re doing this study is a number of extremely interesting case studies.

Case Study: Joey No Floors Freshwater

The earliest case study comes from Joey “No Floors” Freshwater, who shared his story on twitter. He did a version of the potato diet consisting of “1-1.5lbs of potatoes a day when I could”. This comes out to about a 20% potato diet, and it turns out the 20% potato diet works quite well, at least for Joey. 

Sadly Joey is no longer on twitter, but we do still have the screenshots:  

Nicky Case Study: Nicky Case

The second case study comes from Nicky Case. Nicky participated in the original potato diet study and lost more than 10 lbs over four weeks, without much difficulty. This is kind of striking because Nicky was pretty lean to begin with.

After the potato diet ended, her weight slowly climbed back up. So 50 days after the end of the potato diet, she started a half-tato diet (“at least ONE meal per day is potato”). On the half-tato diet, she lost weight at about half the rate she did on the potato diet, and described it as “TRIVIALLY EASY to do”. Here’s the figure: 

This is very encouraging. Nicky tried both the potato diet and the half-tato diet for more than 40 days each, and the direct comparison makes it pretty clear that the half-tato diet caused about half as much weight loss, at least for her. 

Case Study: M’s Potatoes-by-Default

Our third case study comes from M, a reader whose email we published in December as a Philosophical Transactions post. 

M tried a version of the potato diet he calls “potatoes by default”. He describes this approach like so:

If I didn’t have anything better to eat, I’d eat potatoes. This meant that if I had plans for lunch or dinner, I would eat whatever it was I would’ve normally eaten ad libitum, and I tried actively to prevent the diet from materially interfering with my lifestyle (I drank alcohol socially as I normally would’ve, I participated in all the meals I normally would’ve participated in with friends, I tried arbitrary new dishes at restaurants, etc.). … In practice, “potatoes by default” meant I was eating potatoes for roughly 1/3 of my meals, mostly for lunch when I was working from home during the week or on weekends, since I usually had dinner plans of some kind. 

This relatively potato-light approach caused surprisingly rapid weight loss. M describes it like so: “I think my main reaction to the data was that it was kind of insane? I was eating potatoes a third of the time and literally whatever else I wanted the rest of the time, and losing weight almost as quickly as the full potato diet.” 

Here’s the figure. The chart on the right is just a zoomed-in version of the chart on the left, the vertical red line is when he began the potato diet, and the gray bars are when he was traveling and ate no potatoes:

The orange dots in this plot follow the daily averages for the full-tato diet we did. You can see that they are very similar to the blue dots, which are M’s data. When M says that he was losing weight almost as quickly as the full potato diet, he wasn’t joking. While the half-tato diet worked about 50% as well for Nicky, “potatoes by default” seemed to work much better than 50% for M. 

You’ll also notice that M kept on “potatoes by default” for much longer than 30 days, and while the weight loss seems to slow a bit near the end, he keeps losing weight for basically the whole period covered in the plot. He loses more than 10% of his body weight over about three months! And he wasn’t even getting that many calories from potatoes — only like 30%!

Design

That’s why we are running a half-tato diet community trial. Let’s take a look at the design!

Half-Tato Diet Protocol

The half-tato diet is very flexible. As long as you are getting around 50% of your calories each day from potatoes, you’re on target. 

Here are three ways of doing half-tato:

❖ True Half-Tato: Try to get 50% of your calories from potatoes each day, however you want.

❖ Potatoes-by-Default: This is M’s plan, and it worked well for him. Basically, if you don’t have any other plans for a meal, eat only potatoes (a little cooking oil and spices/hot sauce are ok, but nothing substantial). Otherwise, if you are seeing friends or going on a date or anything else, eat as you normally would. If you choose this plan, consider taking a close look at M’s email to us where he describes his protocol in more detail.

❖ Potato Meal: Have one meal a day be nothing but potatoes (with basic spices, etc.). For other meals, eat as normal. This is basically what Nicky Case tried for her half-tato diet. She describes it as “½ the weight-loss effect, but it was *much* easier than Full-Tato. Trivially easy, even.”

On the signup sheet (linked below), we will ask you to indicate which approach you are planning to follow. You don’t have to stick with the approach you choose, but it will be good to know which approaches are most popular, and if there happens to be a big difference between these approaches for some reason, maybe we’ll be able to pick up on it.

When you’re not eating potatoes, please eat as you normally would. The goal is to see how the diet works when you otherwise eat, exercise, and live as normal, so try not to change too much. 

We do, however, have two small suggestions.

In the original potato diet study, we asked people to try to avoid dairy. But now we are not so worried about it. For the half-tato diet, please feel free to continue eating dairy if you want. We will just ask you to track the number of servings of dairy you eat each day on your data sheet. That way, on the off chance that dairy does make a huge difference, we may be able to detect it.  

The second has to do with tomato products, especially ketchup. We reached out to the case studies we mentioned above, and most of them told us that they didn’t have ketchup with their potatoes, or didn’t have it very often, so “no ketchup” may be important for the half-tato diet to work. You may want to avoid tomato products and not have ketchup with your potatoes, but it’s really up to you.

Like with dairy, we will just ask you to track the number of servings of tomato products you eat each day on your data sheet. That way, if tomatoes stop the potato effect for some reason, we may be able to detect it.  

To sum this up:

• Get around 50% of your calories from potatoes each day, using whatever method (one potato-only meal a day, potatoes-by-default, etc.) you like.
• Start with whole, raw potatoes when you can, consider cooking them in a way that keeps them as whole as possible.
• Otherwise, eat as you normally would. Don’t consciously eat better, but also don’t consciously eat worse.
• On the spreadsheet we share with you (below), track your weight, approximate percent potato for each day, your energy, mood, and the ease of the study, as described on the sheet.
• Track servings of dairy just in case, don’t bother avoiding it if you don’t want to.
• Track servings of tomato products, just so we can see if there’s a difference. Maybe consider avoiding them, especially if you’re not losing weight.
• Track any bonus variables you’re willing/interested to track.

On the first day of half-tato, start eating potatoes as per the approach you chose above (e.g. potatoes-by-default). As long as you are feeling ok, keep trying to stick with it. The effect sometimes takes a couple days to become clear; there’s lots of variation between different people; you may lose a little weight one day and gain weight the next; don’t worry if the effect takes a little while to show up.

If you start feeling bad or weird, try one of these helpful hints:

• Eating a potato (or something else). Hunger feels different on the potato diet and you may not realize that you are hungry. Yes, really. 
• Drinking water.
• Eating a different kind of potato. Different varieties of potatoes may seem like they’re all pretty much the same, but they can really be quite different, and if you’re eating a lot of potatoes, these differences become much easier to notice. You will almost certainly want to eat more than one kind of potato.
• Peeling your potatoes. Eating less peel / no peel seems to help some people with digestive and energy issues, especially after a few days on the diet.
• Eating more salt. Potatoes are naturally low in sodium and you may not be getting enough. They’re also high in potassium, which can throw off your electrolyte balance if you don’t get enough sodium to match it. 

If you try these things and still feel bad or weird, take a day or two off the half-tato diet and just mark down on your sheet that 0% of your food (or whatever) for those days was from potatoes. 

If you start feeling really bad, or you otherwise can’t make the half-tato work for you, just stop the trial early. We don’t want anything bad to happen to you. Just send us an email to close out the trial as normal (see below).

Two-Week Baseline

In our previous community trials, we didn’t include a control group. This is because we expected the effect sizes to be ginormous. People don’t, generally speaking, spontaneously drop 10 lbs in four weeks, so it’s clear the weight loss on the potato diet is “real” without the need for a control group.

This worked less well for the potassium trial, but we wanted to get the biggest sample size we could for that study, and we weren’t sure how many signups we would get beforehand. We stand behind the idea that when you’re trying to estimate an effect size, it’s good to get as many people in the experimental condition as possible.

We’re still not going to include a control group, because we don’t think it would be very interesting to recruit half of you to sit around and do nothing for several weeks, and it wouldn’t teach us very much. 

But we will do the next-best thing, and that’s to ask you to take a baseline of your weight change without the half-tato diet. For the first two weeks of the study, eat as you normally would, and track your weight over time. Then on the fifteenth day, start the half-tato protocol and get on to eating lots of potatoes. It’s simple.

This lets us use everyone as a control group for themselves, sort of like a crossover design. While this design wouldn’t work for everything, we think it works pretty well for the half-tato diet. 

Variable-Span Signup

We’d like you to try the half-tato diet for at least four weeks. With the two-week baseline, this is a total commitment of six weeks.

But if you’re willing to go further, we would be really interested to have that data. So for the half-tato diet community trial, we are opening things up and letting people enroll for however long they want.

Credit where credit is due, this part of the design was Nicky Case’s idea. She describes it as a “hey this trial runs for however long you want, and we’ll just report data every month for whoever hasn’t dropped out yet” design, and we think it makes a lot of sense.

This is a bit like what we did with the potassium trial — we asked people to keep going to 60 days if they were willing, some did, and we reported on their data in a second analysis post. We want to do the same thing in this study, except that we’d like to ask you to sign up for longer spans up front, if you’re willing.

We won’t hold you to this. It’s not a commitment. We’d just like to know up front how long you’re planning to sign up for. If you can’t make it that long, that’s fine. Just tell us how long you’re thinking you might try. 

(Obviously you can also keep going for longer if you want, don’t let us stop you.)

For example, you can sign up for:

• 2-week baseline + 4-week half-tato
• 2-week baseline + 8-week half-tato
• 2-week baseline + 12-week half-tato

And so on and so forth, all the way up to 2-week baseline + 68-week half-tato. We will take snapshots of the data at relevant intervals and analyze the data up to that point. 

Sure, “report every month on whoever hasn’t dropped out yet” has a selection bias. The people who sign up for 52 weeks will not be your average ordinary citizens. In fact, they will be paragons, heroes. But that doesn’t concern us. We still want to see those data.

And if you sign up for 52 weeks but it turns out no one can actually be bothered to do half-tato that long, that’s still useful data. Just think about it. 😉 

Sign Up

Ok researchers, time to sign up.

The only prerequisites for signing up are: 

• You must be 18 or older;
• In generally good health, and specifically with no kidney problems;
• Willing to do a two-week period of baseline measurements; 
• Willing to get about 50% of your calories every day from potatoes, as described above, for at least four weeks, and;
• Willing to share your data with us.

As usual, you can sign up to lose weight, lower your blood pressure, get more energy, or see one of the other potential effects. But you can also sign up to help advance the state of medical science. This study will tell us something about nutrition, weight loss, and obesity. If the half-tato diet works for most people, it will give us a practical weight-loss intervention that’s much easier than the 100% potato diet.

And beyond that, running a study like this through volunteers on the internet is a small step towards making science faster, smarter, and more democratic. Imagine a future where every time we’re like, “why is no one doing this?”, every time we’re like, “dietary scientists, what the hell?”, we get together and WE do it, and we get an answer. And if we get a half-answer, we iterate on the design and get closer and closer every time. 

That seems like a future worth dreaming of. If you sign up, you get us closer to that future. We hope that this is only the beginning of what will be a century full of community-run scientific trials on the internet. Maybe by 2030, the redditors will have found a way to triple your lifespan. But for now we are doing potato.

Eating this much potato may sound a little daunting, but people who have tried it say that it is much easier than they expected, and delicious to boot. Here’s our suggestion: If you are at all interested in trying the half-tato diet, go ahead and sign up and start collecting your data. Collect your baseline measurements for two weeks, then try the first day or two of half-tato and see how it feels. If you hate it and have to stop, we would still love to have that data.

If at any point you get sick or begin having side-effects, stop the diet immediately. We can still use your data up to that point, and we don’t want anything to happen to you.

We are mostly interested in weight loss effects for people who are overweight (BMI 25+) or obese (BMI 30+), but if you are “normal weight” (BMI 20-25) you can also sign up. The original full-tato diet caused weight loss in people of normal weight, and it would be interesting to see if the same thing happens for the half-tato. 

And for everyone, please consult with your doctor before trying this or any other weight loss regimen. 

If you were part of the original SMTM Potato Diet Community Trial, or the SMTM Low-Dose Potassium Community Trial, please feel free to sign up for this study as well! We know that most people who were part of the Potato Diet Community Trial have returned to their baseline weight in the last 6 months, so the original results shouldn’t interfere. And it will be very interesting to compare your weight loss on the half-tato diet to your weight loss on the full-tato diet. Since we can make direct within-person comparisons, this will give us a much better sense of if the half-tato diet works half as well (or better; or worse) as the full-tato diet.

Anyways, to sign up: 

1. Fill out this google form, where you give us your basic demographics and contact info. You will assign yourself a subject number, which will keep your data anonymous in the future.
2. We will clone a version of this google sheet and share the clone with you. This will be your personal spreadsheet for recording your data over the course of the diet.
3. On the first day, weigh yourself in the morning. If you’re a “morning pooper”, measure yourself “after your first void”; if not, don’t worry about it. We don’t care if you wear pajamas or whatever, just keep it consistent. Note down your weight and the other measures (mood, energy, etc.) on the google sheet.
4. For the first two weeks, eat as normal and continue to track your weight and other variables to provide the baseline. Then when the two weeks of baseline are complete (clearly marked on the data sheet), start eating about 50% potatoes, and continue with the half-tato diet for however long you signed up for (4 weeks or longer).
5. We prefer that you try to get around 50% of your calories from potatoes for at least four weeks. But imperfect adherence is ok. If you only get 30% of your calories from potatoes one day, or you have to skip a day entirely, that’s all right. Just note it down on your sheet. We’re interested in how the diet works for normal people at home, with all the complications that entails.
6. When you reach the end of the diet (whether you’re ending the diet early, reaching the span you signed up for, or going beyond it), send us an email with the subject line “[SUBJECT ID] Half-Tato Diet Complete”. This will give us a sense of how the study is proceeding in general and is your opportunity to tell us all about how the study went for you. Please tell us any information that doesn’t easily fit into the spreadsheet — how you felt, what kind of potatoes you used, how you prepared them, before and after pictures (if you want), advice to other people trying this, etc. There’s a chance that the half-tato approach will work for some people and not for others, and if that happens, we’ll dig into these accounts to see if we can figure out why.
7. Remember that it is ok to end the study early if you need to, for example if you get sick, or if you decide that 12 weeks or whatever is too long of a commitment. It’s also fine to reach 12 weeks and keep going if you’re having a good time. Just make your intentions clear in the comments on your data sheet and send us an email whenever you decide to finish, we’d love to hear from you.

Assuming we get 20 or so people, we will write up our results and publish them on the blog. We would really like to get a couple hundred people, though, since at that point it becomes possible to do more complex statistical analyses. So if you think this is an interesting idea, please tell your friends!

Most diets help people lose a little weight. But once you go off the diet, the weight usually comes right back.

But what about the potato diet? In our recent community trial, people lost an average of 10.6 pounds over only four weeks on the potato diet, and the weight loss was very reliable. Of the people who finished four weeks on the diet, all but one of them lost weight, and a few people lost more than 20 pounds.

Most diets are not nearly this effective. The potato diet seems unusually good at causing weight loss. Could it also be unusually good at maintaining weight loss after people stop eating potatoes? 

There are some signs that it might. The potato diet was partially inspired by several case studies, and the case studies suggest that the weight you lose on the potato diet stays off, at least for a while. We focus on three case studies in particular:

Chris Voigt lost 21 lbs on a 60-day potato diet back in 2010. It’s not clear if he gained that back or not — this article from 2018 doesn’t mention it either way. He looks pretty lean in photos, but then again, he was pretty lean to begin with.

Andrew Taylor did an all-potato diet for a full year and lost 117 pounds. This was 7 years ago and he seems to have kept most of the weight off since then. Of course, Andrew did the potato diet for a full year, and was pretty strict about it, so his experience might not generalize to people who did the potato diet for only four weeks. 

And of course, Penn Jillette, of Penn & Teller fame, lost over 100 lbs on a diet that started with a two-week period of nothing but potatoes. This was way back in 2014, and despite only doing potatoes for two weeks, he seems to have kept most of the weight off as well.

In these cases, especially the last two, it seems like the potatoes have somehow reset these people’s lipostats, the system in the brain that keeps you at a particular weight. Their lipostats used to be really high for some reason; then they did a potato diet; now their lipostat seems to be defending a set point about 100 pounds lower. 

The good news is that we now have a larger sample to work with, so maybe we can finally get at some of these questions. It has been about 6 months since the close of the SMTM Potato Diet Community Trial, and this is the 6-month followup analysis.

Method

We sent an email on January 1st, 2023 to everyone who had participated in the Potato Diet Community Trial, asking people to fill out a short 6-month followup survey.

In this survey, we asked them for:

• Their potato diet participant ID, so we could connect their responses to the original results
• Their current weight
• How much potato they continued to eat post-study
• If they participated in the SMTM potassium trial
• And any general comments

We gave people approximately two weeks to fill out this survey. Then on January 14th, we downloaded the data.

There were a total of 53 responses by this point.

The majority (51 of them) were people who we analyzed in the original trial.

Of these, 32 were people who made it the full 4 weeks in the original trial. This happens to be exactly half of the 64 who originally made it to 4 weeks.

When we did the original analysis of the potato diet, there were still a few people who were in the middle of their four weeks of the diet, so we didn’t analyze their data at the time. Two of those people responded to this followup survey. They were not in the original analysis, but they did both complete four weeks, so we are going to include them in this analysis. 

So in total we have 34 people who completed 4 weeks on the potato diet and then reported back at the 6-month check-in. This is our main group of interest.

One person (participant 24235303) reported being 136.4 lbs at the 6-month followup, but he was 222.2 lbs at the end of the potato diet, so this would mean he had lost 85.8 more pounds over the intervening 6 months. Because this seems unlikely, and because his comment was, “my weight drifted back up over a few months”, we assumed this was a typo. We followed up by email and he confirmed that he meant to type 236.4 lbs, so we corrected this number for the analysis. 

Participant 63746180 reported being pregnant (congratulations!) so we are excluding her data from this analysis as her weight may not be representative. 

Participant 65402765 mentioned that they “started semaglutide around the same time as potato diet”. Semaglutide (sold under brand names like Ozempic and Wegovy) is an anti-obesity medication, so while this participant did lose 13.4 lbs in this 6-month period, we also excluded their data from the analysis. 

Because of these exclusions, the final sample size for the rest of the post is 32 people.

All new data and materials are available on the OSF.

Results

On average, people gained back most of the weight they lost. This subset of people lost an average of 11.1 pounds from Day 1 to Day 28, and from Day 28 to the 6-month followup there was on average 10.3 lbs of weight re-gain.

People are on average down 0.71 lbs from their starting weight on Day 1 of the original study, but this is not significantly different from zero. On average, people are pretty much back to baseline.

In aggregate, it looks like a pretty strict reversion to the mean — people lost a little more than 10 lbs over 4 weeks on the potato diet, and gained back almost all of that weight over the next 6 months. 

This is still a relatively successful weight loss intervention — you do a diet for just one month and it takes about 6 months to gain back the weight you lost. This suggests that if you were willing to do a week or two of potato diet every 3 months, you could probably keep your weight down indefinitely.

But just looking at the averages conceals a pretty drastic spread. When we plot the results, we can see that 6 months later, most people are back near baseline, maybe slightly under baseline on average. But some people are down almost 20 or 30 lbs, some people are up more than 10 lbs, and one person is up almost 30 lbs! 

That central cluster is what gives us the average. Most people gained weight in the 6 months after the end of the potato diet, and ended up on average slightly under baseline. 

Four people kept losing weight (one of them isn’t obvious in the plot, they were near the top of the pack at Day 28 and are near the bottom of the pack at the 6-month check-in), and three of those people ended up down more than 15 lbs over 6 months. Those three are the clear outliers below the main group at 6 months.

Five people gained back way more (10+ lbs) than they lost. These are the five dots way above the main group at 6 months, including that one dot that is up at nearly 30+ lbs. 

It may be hopeless to try to figure out what is different about these eight or so people, given the small sample size, but let’s try.

Outliers

Since there are so few outliers, let’s start by looking at them one-by-one.

Participants ​​99065049, 82575860, 66459072, 10157137, and 77742719 all ended up more than 10 lbs heavier than their baseline on Day 1 of the potato diet. 

Participant ​​99065049 is the outlier, having lost 6.3 lbs in the trial and gained back 34.5 lbs since then, for a total gain of 28.2 lbs since Day 1. We wanted to double-check this result, so we reached out to this participant over email and he confirmed that it was not a typo.

This group didn’t say much about themselves in the comments. Only two of them left responses at all. Participant 10157137 said: 

After the potato diet my cholesterol had improved, but post diet it shot back up again 😔

Participant 82575860 said:

Would appreciate a follow up post on the best potato-based recipes that were sent in 

Participants 20943794, 19289471, and 35182564 lost the most weight. All of them lost more than 5 lbs on the potato diet, and kept losing weight after that. Their total weight loss by 6 months was 19.3 lbs, 23.2 lbs, and 28.7 lbs, respectively. 

Participant 35182564, who lost the most weight, said:

Weight is incredibly stable, although I eat normal, just like before the potato diet. This was a great success.

Participant 20943794 offered the most detail, saying: 

After the potato diet ended, I started a pretty traditional CICO diet using the Noom app. Roughly speaking, I lost 10 lbs on the potato diet, and another 10 on the CICO diet. 

Before the potato diet, I tried calorie counting and various high-protein, low carbohydrate diets, and have never had this kind of sustained success. (E.g., I’ve lost 20 – 30 lbs before, but I didn’t maintain that weight for more than a month or so). 

In addition to the potato diet, there are some other confounding factors: 

1. Whey protein has figured heavily in all my previous diet regimens, but I obviously didn’t take any during the potato diet, and even after it ended, I drastically cut back how much protein powder I consumed (because of the lithium hypothesis) 

2. Because of covid and it’s after-effects, I eat out far less frequently than I ever did before. Since January 2020, I’ve eaten restaurant food (whether dine-in or take-out) only about a dozen times (most of that was on a business trip in October 2022). Before that, I’d say I ate restaurant food on average once per week

Moving on from the comments, we can see if any of the other variables offer us insight.

The potato diet included people from all weight brackets, and maybe that’s what is causing this confusing pattern. For example, maybe all the outliers who gained weight over baseline are people who were slightly underweight when they started the potato diet, and who have gone up to a healthy weight 6 months later. Maybe all the outliers who lost extra weight were very heavy people whose lipostats were easier to reset. 

But when we plot the results by BMI bracket, we see basically no pattern: 

Another possibility is that this reflects whether or not people kept eating potatoes after the trial was over. After all, you can eat potatoes without being on the potato diet, and many people do. Perhaps the people who kept losing weight are the people who stuck with the potato diet, even if only casually, for the long-term. And maybe the people who gained extra weight grew disgusted with potatoes and stopped eating them entirely. 

The good news is that we collected this very variable. But again, when we plot it, we see no such thing: 

The person who lost the most weight ate “way less potatoes than [they] used to”. The people who gained the most weight are all in the middle. No clear pattern here.

That said, if you plot this variable WITHOUT the outliers, you see basically what we would expect — people who kept eating more potatoes are mostly still below their original weight, people who didn’t change their potato intake are back to baseline, and people who are eating way less potato than they used to are slightly above baseline. 

Finally, here’s a breakdown by country. Most participants are Americans but take a look: 

American Holidays

Most of our participants are Americans, and in the span between the start of July and the end of December there’s a major American holiday period that famously involves a lot of eating: the period from Thanksgiving to New Year’s.  

As a result, at the 6-month followup our participants were asked to weigh themselves just after a period of especially serious and far-ranging eating. Quite possibly they were being asked to weigh themselves at the heaviest they would be all year.

So in some ways, the particular timing of how this all worked out is a rather conservative test of the potato diet. The weight loss from the potato diet does not seem to survive the holiday period, but it might last somewhat better across any other 6-month span.

A number of our participants commented on this as well. Let’s take a look: 

(57875769) For about the first month after doing the trial my weight continued to trend downward although much more slowly. Then it slowly started creeping back up. Most of the weight came back during the holidays (it’s a little unfortunate that the six month follow up landed right after Thanksgiving, Christmas, and New Years!).

(89852176) After ending the full potato diet about 10 pounds below my typical weight, I returned rather quickly to my baseline (spurred on by eating at family vacation) and stayed there for several months. I ended the year roughly 5 pounds higher than baseline, all of which were gained in the second half of December with “typical” USA holiday (over-)eating.

(63187175) Gained about 5 pounds over the holidays, I was closer to 235 at the beginning of December

(50913144) I stayed at the lower weight for a few months, it only started creeping back up at pre-potato-trial rates in the last 6 weeks or so.  I am probably going to do another round of potato intervention, i don’t like the potassium and it doesn’t seem to help me much. 

(15106191) This measurement is being taken just after the holidays. This is higher than my pre-potato weight but I don’t blame the potatoes, its normal for me to weigh about this much more in January than I did in June

This is also somewhat supported by Nicky Case’s followup survey, which she conducted separately (with our peer review) and ran before the holidays. On October 30th, 2022, she put out a survey on the potato diet, asking people about their current status. She only got 9 responses, but found that most people were still below baseline and had kept most of the weight off.

If we expand our plot using her data, we can see that some people were down quite a bit more in late October / early November than they were at our 6-month check in.  

Some people, however, mentioned gaining the weight back more quickly: 

(25547207) It took about a two months to gain all my weight back. My strength training had to cease 2 weeks in for the remainder of the study, and my large lifts dropped about 10%. It took about 1 month to recover my original strength and I was making gains before fully recovering my weight.

(72706884) I gained back all the weight within 3 months

Conclusions

The potato diet causes very consistent weight loss. But whatever makes the potato diet work doesn’t permanently change your set point. The first thing we see is that most people gain back the weight they lost over time, and on average, it looks like they are back close to their original weight about six months later. 

Unless it did permanently change the lipostat for those three people for some reason. Because the second thing we see is striking individual differences. A small number of people ended up weighing 10+ pounds more or less than they did when they signed up for the trial, and it’s not clear why. 

Maybe they had unusual life circumstances that happened to make them lose or gain more weight over those six months. Maybe they are just random outliers. Or maybe they are more/less sensitive to potatoes for some reason, more sensitive to whatever the active ingredients are. Something something cybernetic attractor states.

There’s a chance that the outliers who kept losing weight are just noise, or that they would have lost weight anyways for some other reason and just happened to sign up for the potato diet at the right time. But there’s also the chance that there is something different about these four participants. If we could figure out what that difference is, maybe we could create lasting weight loss for everyone. For example, are these four people the only four vegans in this sample? We didn’t think to ask this question, but if they were, that would be very interesting. A potential extension then would be to do a much larger potato diet study (1000+ participants) and keep special track of the people who kept losing weight after the trial ended. 

Still, the potato diet is a relatively successful weight loss intervention, since one month of dieting gives consistent results that tend to stick around for about six months. And given the significant individual differences we see, it seems that for some people the effects are more lasting. While we don’t know why this happens for some people and not for others, there’s a small chance that you’ll end up being one of these outliers, and you’ll keep losing weight after the potato diet is over.

We will probably still do the 1-year followup to keep up with these outlier participants, and to see if overall average weight remains below the original baseline or not. But in general, it seems like the conclusion is that 4 weeks of potato diet will make you lose weight, and six months later most people will be back around baseline.

The first time we mentioned the potato diet, in Part III of our series A Chemical Hunger, we shared the story of Chris Voigt, the Executive Director of the Washington State Potatoes Commission, who lost 21 pounds on a 60-day potato diet. By Part X of the series, we started to wonder if someone should maybe run a study, and see if the potato diet really works as well as all that. 

For those of you who are just joining us, the potato diet is a diet where you try to get most of your calories (>95%) from potatoes. You can have drinks like coffee and tea. You can season the potatoes with salt, spices, and whatever hot sauce you want. You can even cook with oil. The only thing we asked people to entirely avoid was dairy (see original post for details). 

Does this mean you can eat fries for every meal? It does, and some people came pretty close to that ideal. See for example, this post:

I have never heard of a diet that allows you to eat french fries for all three meals, and I did just that on a couple of days. It rocked.

Or:

But we’re getting ahead of ourselves.

TABLE OF CONTENTS

1. Background
2. Variables
3. Demographics
4. Weight Loss
5. Effects other than Weight Loss
6. Why do Some People find the Diet Easy and Others Don’t
7. Why the Heck Does the Potato Diet Work
8. How to Potato Diet if you want to Potato Diet
9. What’s Next

1. Background

We announced the first Potato Diet Community Trial on April 29th 2022, in a post titled, “Potato Diet Community Trial: Sign up Now, lol”. We announced the trial on twitter, and on the SSC/ACX subreddit. Signups opened the same day. We asked people to try the diet for four weeks

As people signed up and started sharing their experiences, we made a twitter thread of live-ish updates. In this thread you can read anecdotes shared on twitter that aren’t found in the official study data.

To sign up for the study, participants filled out a google form (PDF available in the repository; see below) of demographic information, then over the next four weeks, recorded their data on a copy of a google sheet that we provided.

Two hundred and twenty people filled out the signup form before we closed the study. As far as we can tell, most signups came from twitter, reddit, and word-of-mouth. We actually didn’t ask about this, probably should have. Whoops.

Signups closed on June 3rd, 2022, four weeks after we announced the diet.

We downloaded people’s data when they sent us an email to formally close the study. Anyone who didn’t send us an email to officially close the study, we grabbed their data (if any) in the last days before closing the study. The dataset we’ll be examining today represents the state of the data as of midnight on Friday, July 1st, 2022, four weeks after we closed signups and eight weeks after we started collecting data.

Raw data, the analysis script, and study materials are available on the OSF. We decided to store our data and materials there, since that repository is well-supported and we expect it to stay available for a long time. The organized data is “SMTM Potato Diet Community Trial Main Form.csv”; the script is called “SMTM Potato Diet Community Trial 1 Analysis.R”; and the raw data is in a folder called “Potato Raw Dato” 

This dataset is very rich — we certainly haven’t found everything there is to find in these data. A number of people measured other variables (like blood pressure, resting heart rate, and sleep) and we haven’t looked at those data in any systematic way.

Also there is a lot of room for new findings in coding the free-response data. You could, for example, go through and try to code what kind of oil(s) people are using, and see if people who use different oils lose different amounts of weight, find the diet easier, etc.

We really look forward to seeing other people do their own analyses. Send them our way, we’ll link them or do a roundup post or a meta-analysis or something.  

Two participants asked that we not share their data publicly. But if you’re following along at home you should still get the same results as we do, because those two participants seem to have entered no data.

If you have advice about what to do differently next time, we are interested in hearing that. But if you don’t like something about the study design and just want to gripe — run your own study!

2. Variables

Let’s start with a recap of the study variables.

Our demographic variables are — age, ethnicity, height in inches, local ZIP or postal code, current country of residence, profession, and reported sex. 

Sex was initially reported as “Male”, “Female”, or a free-response “other” field. A few participants reported being trans or nonbinary, so we created two variables, “Chromosomal Sex (estimated)” and “Hormonal Profile (estimated)” where we estimated their chromosomal sex and hormonal profile, respectively, based off of free report data. As the names suggest, these are just estimates. We don’t actually have access to your chromosomes.

This is in case there end up being major endocrinological effects. It seems like there could be sex differences in the potato diet because there are clear sex differences in obesity and in anorexia, which we think may be related.

On their datasheets, participants were asked to record a slate of variables every day. Our main daily variables are — daily weight in pounds; notes for each day; energy for each day on a scale from 1-7, where higher numbers are more energy; mood for each day on a scale from 1-7, where higher numbers are a better mood; and ease of the diet for each day on a scale from 1-7, where higher numbers are finding the diet easier.

We also had a field where participants could record whether or not they broke the diet (eating something substantial other than potatoes) each day. If they stuck to the diet we asked them to put a 0 in this field, if they broke the diet we asked them to put a 1. This is a bit of a mouthful so we will often colloquially refer to these as “cheat days”.

3. Demographics

A total of 220 people submitted the initial form.

Of those, 11 people filled out the signup form incorrectly in such a way that we couldn’t sign them up (they didn’t enter an email, didn’t indicate critical data such as height, etc.). We enrolled the remaining 209 people in the study.

Let’s take a look at the demographics of the people who enrolled: 

• Age ranged from 18 to 69, with a mean of 35.2 and a median of 35. 
• Reported sex was 50 female, 151 male, 7 other entries (e.g. “non-binary”, “AFAB on testosterone so idk how you wanna categorise that”), and one person who didn’t respond.
• Based on this, we estimated 51 XX participants and 156 XY participants; and we estimated 53 people with a more “female” hormonal profile and 153 people with a more “male” hormonal profile.
• Reported ethnicity was 185 white, 10 Asian, 2 Indian, and 4 more specific entries (e.g. Latin, Indonesian, etc.). Everyone else who reported ethnicity reported being a mix (e.g. “Brazilian. Mostly white, kinda mixed though.”; “German/Vietnamese/Anglo-Saxon“).
• Participants mostly came from the Anglosphere and Europe: 133 US, 17 UK, 17 Canada, 7 Germany, 6 Australia, 4 Ireland, 3 Sweden, 2 Poland, 2 India, 2 Hungary, 2 France, and several singletons from places like Finland, Mexico, Serbia, Brazil, and “Magyarorsz√°g” [sic] which we think is also Hungary.
• Profession is hard to code since it’s so diverse, but it looks like the biggest groups were software engineers/programmers, grad students, various scientists and academics, and game designers.

Out of the 209 people signed up, 5 started the diet late for one reason or another, and were still in the middle of the four weeks when we closed data collection on July 1st. We let them keep going and looked at the 204 people remaining.

Of these 204 participants, 44 never entered any data onto their datasheet. As far as we can tell, they just never got around to starting the diet — we certainly didn’t get any data from them.

This leaves us with a total of 160 people who entered some data. Of those 160:

• Age ranged from 19 to 61, with a mean of 36.0 and a median of 35.5. 
• Reported sex was 29 female, 124 male, 6 other entries, and one person who didn’t respond.
• Based on this, we estimated 30 XX participants and 129 XY participants; and we estimated 32 people with a more “female” hormonal profile and 126 people with a more “male” hormonal profile.
• Reported ethnicity was 145 white, 5 Asian, and 10 other entries like “Polish” or “Japanese/ Hispanic”.
• Participants were still largely Americans: 104 US, 13 Canada, 12 UK, 6 Germany, 5 Australia, 3 Sweden, 2 Poland, 2 Ireland, 2 Hungary, and one each to a number of others.
• Again the most common profession is software engineer / programmer, with various research jobs and IT jobs behind it.

Of this group, 35 people formally closed the diet early by sending us an email. We coded the reason they dropped out based on their comments.

One we coded as dropping out because of boredom (“Overall not a difficult diet, but I decided to end it because I was getting pretty bored of potatoes.”).

Two reported stopping because they got sick, which we coded as illness. This isn’t potato-related illness, to be clear — one had a throat infection and the other got shingles.

Six reported stopping because of a schedule conflict, coded as schedule. Some of them specifically said they could have kept going otherwise, like participant 66959098: 

I am ending my diet at 21 days instead of at 28. This is mostly a scheduling issue, having family visiting next week and would like to go out and eat with them. I believe I could have made the four weeks without too much trouble otherwise, and I may even go back on the diet again sometime later. 

The remaining 27 early closures reported stopping because they found the diet really difficult in one way or another, and we coded this as difficulty. For example, participant 29957259: 

I threw in the towel on the potato diet six days in. The first few days were easy for me, but it eventually grew much more difficult. I found myself thinking about food way more than someone whose next meal was planned should have.

Clearly the potato diet really does not work for some people! More on this later.

Another 57 people made it partway to 4 weeks but didn’t officially close the study, and we don’t know why. We went back and forth on what to call this, since we don’t know why they stopped reporting their data, and we wanted the coding to sound as neutral as possible. In the end we coded them as dropped. 

These participants don’t seem to have just flaked out. Many of them made it a long way. Several people made it past two weeks, and two people made it all the way to day 27:

We’re going to try to stay agnostic about what happened in these cases, because these participants didn’t give us a clear reason why they dropped out. But we can also make some educated guesses. 

Some people clearly dropped out because the diet was too difficult. For example, participant 31554252’s last comment was: 

Finding it very difficult to keep going—just very sick of potatoes

But other people don’t seem to have found the diet difficult, and probably dropped out for other reasons. For example, participant 71309629 appears to have dropped out because of illness. They said, “Got sick, will update later” on the last day they entered data, and haven’t updated since. We hope you’re ok!

Similarly, participant 97388755 could probably be coded as ending for schedule reasons. She said in the comments:

I renounce potato. I’m moving house and the chocolate cravings and trying to make potatoes for 2 people is a pain in the ass.

It might be interesting to go back and try to re-code all the dropped trials, figure out why they stopped the diet, but not today.

Since we asked everyone how easy the diet was, we can also look at the ease they reported on the last day they gave us a weight measurement (though a few people stopped reporting ease before then). As a reminder, higher numbers / more to the right is more easy:

Some people definitely were finding this difficult when they stopped, and it’s reasonable to think that the people who gave a 1 or 2 on the last day stopped because they couldn’t stand it.

But plenty of people who dropped out without telling us why rated diet ease at a 6 or a 7. The modal value is clearly 5! So while some of these dropped trials are because of difficulty, others presumably dropped out for other reasons: they had to go on a trip, they had a family emergency, they got sick with COVID, etc.

The diet protocol in the original post asked for 29 days of weight measurement. The last measurement would be on the morning of the 29th day, giving us 28 days of complete data.

But we fucked up on the data recording sheet and made it seem like people should record only up to day 28. Most people followed instructions — they gave us 28 days of data, then stopped. This is our fault, we messed up.

To keep things standard, we used each person’s data at day 28 as their final day of data. For people who went past 28 days (a number of people kept collecting their data and/or kept going with the diet), we treated them as if they did 28 days exactly. We used their weight on day 28 as their final weight, counted their number of cheat days up to day 28, etc. 

At some point it might be interesting to go back and look at the data of people who did 29+ days, but again, not a project for today.

This is technically 27 full days of potato diet, since the measurement for day 28 is the MORNING of day 28. But tiny differences like this are like, eh, who cares. If the effect is substantial at all, it won’t matter anyways. Anyways, henceforth this span will be referred to as “four weeks”.

One participant (40207077) didn’t report his weight for day 28, so we used his day 29 data. Coincidentally this is also the person who lost the least weight over the 4 weeks. If you kicked him out because he often forgot to report his weight, average weight lost on the diet would be even greater.

Anyways, 64 people made it the full four weeks and completed the potato diet. Let’s review their demographics: 

• Age ranged from 19 to 61, with a mean of 36.7 and a median of 36.5.
• For sex, 5 reported their sex as female, 54 male, 4 other entries, and one nonresponse.
• We estimated 6 XX and 57 XY; and we estimated 7 people with a more “female” hormonal profile and 56 people with a more “male” hormonal profile.
• For ethnicity, 57 were white, 4 Asian, 1 Polish, 1 “several of the above”, and 1 “half-asian, half-white”.
• Participants reported being in the following countries: 46 US, 4 Canada, 2 each in UK, Germany, and Ireland, and several singletons.

Racial diversity is definitely a major limitation of this study, especially since obesity differs a lot across ethnicities. The diet could easily work half as well, or not at all, for African-Americans. Or for all we know, it could work twice as well. The results we have so far look really promising (as you’ll see in a minute), and we think it’s important to see if they’ll generalize. So if we run another potato diet study, and you’re part of a racial group that isn’t well-represented in this study (i.e. if you are not white), your data could contribute a lot!

Retention

The first question is, what is the retention rate for the potato diet? Well, it depends how you slice it.

If you want to be maximally strict, 64 people made it four weeks out of 209 enrolled, so 30.6%.

Not too bad. This is a kind of extreme diet, and it would be pretty impressive even if only 30% of people made it to the end. Frankly, we’re impressed so many people signed up in the first place. 

But we think this is too low, in fact. Only 209 people were enrolled in the study, and because some trials were ongoing at closing, only 204 had potentially available results. 64 out of 204 would give us a retention rate of 31.4%.

But of those 204 people, 44 never entered any data. There’s a good chance most of these people never started the study, and shouldn’t be considered dropouts. In this case, retention is out of 160, and 64 out of 160 is 40.0%.

If you wanted to be maximally permissive, you could only count the dropouts who sent us an email to formally close the study. This gives us a total of 102 people, and makes the retention rate 64 out of 102 people, which is 62.7%

(Actually if you wanted to be super maximally permissive, you could only count people as dropouts if they explicitly stopped because of finding the diet difficult. Then retention would be 64 out of 91, or 70.3%.)

So we think the retention rate is somewhere between 40.0% and 62.7%, though you could make a case that the retention rate is as low as 30%. In any case, the idea that between one-third and two-thirds of people get to the end of four weeks on basically only potatoes is pretty wild.

Of course, a hard cutoff doesn’t make much sense. Most people made it some number of days between 1 and 28. Heck, five people ended the potato diet on day 27! 

When we look at the number of days people made it to, we do seem to see two (or maybe three?) clear groups: 

Clearly the most common outcome is to make it the full four weeks. The next most common is to drop out in the first week or so. 

But there’s another bump near the end of the third week, and that seems kind of interesting, especially because some people mentioned hitting a wall at around three weeks. For example, participant 23300304 stopped on day 22 and reported: 

Initially I found the diet extremely easy… However, quite suddenly after about three weeks I started feeling unwell, with low level nausea, headaches and general tiredness. Initially I thought I was falling ill. But I didn’t really show any specific symptoms of illness. After a few days I was feeling so bad I decided to end the diet. I felt better by the end of the first day eating my usual diet again.

Similarly, things were going great for participant 63746180. They had already lost about 10 pounds over 18 days and seemed to be enjoying it. But then:

My reason for ending is that I was hungry to the point of headache and dizziness, but could not force myself to eat a potato.  It was a weird experience, my body was screaming for food but I couldn’t swallow a potato.  I went from pretty happy with eating potatoes to completely unwilling to eat a potato in the span of a day. 

So there might be something interesting with people hitting a wall at three weeks or so. However, as you can see from the histogram, it was a minority of participants.

4. Weight Loss

Of the participants who made it four weeks, one lost 0 lbs (participant 40207077). Everyone else lost more than that.

The mean amount lost was 10.6 lbs, and the median was 10.0 lbs. The 99% confidence interval on the mean is 12.1 to 9.1 lbs of weight loss. The greatest amount of weight lost was 24.0 lbs, from participant 74282722.

We thought this might end up being bimodal — some people going into potato mode and other people just struggling through — but it looks pretty normally distributed around 10 lbs. There’s sort of a little spike around 15 lbs maybe.

We can also look at individual time series data:

And here’s the average over time: 

We can also do these plots as percent weight change, but you’re gonna be pretty disappointed, they look almost exactly the same: 

Actually Why Not Just Look at All The Data

Like we mentioned above, a hard cutoff doesn’t make much sense. Let’s just look at all the data.

Here’s weight change by total number of days completed on the potato diet for all participants who entered data: 

Seems like a clear trend. And it makes sense to us; if you make it 22 days on the diet, you get about 3/4 the benefit of making it the full four weeks on the diet.

We can see that only two people reported a net weight gain on their diet, and of only 2.3 and 0.1 lbs. In addition, twelve people did report exactly no weight change — though nine of them only entered data for day 1, so they couldn’t have lost any weight. It doesn’t look like the potato diet can go “wrong” and you can gain a lot of weight. 

We want to point out that the person who lost the MOST weight (24.8 lbs; participant 71319394) actually ended the diet on day 27 — “I am calling it done a day early, but I think it has gone really well for me and was really easy for about 3 weeks.” — so he doesn’t appear in the “completed four weeks” analyses.

Also note the outlier, participant 89861395, who reported losing 41.6 lbs in 18 days. We assume this is an error, in part because he reported being 296.8 lbs on day 17, and then being 267.0 lbs on day 18, after which point he recorded no further data. It seems unlikely that he lost 29.8 overnight just before closing the study. Probably he lost 11.8 lbs total before stopping, the number suggested by his weigh-in on day 17. 

When we plot this over time, it becomes clear that it didn’t really matter if people “finished” or not:

People lost about a half a pound a day on average, though with quite a bit of variation (we did kick out that one measurement claiming to lose 29.8 lbs in a single day, since it’s probably a typo). There appears to be no meaningful difference in the daily weight loss of people who did and didn’t make it the full four weeks. In fact, people who made it the full four weeks had slightly lower average weight loss, a mean of 0.41 lbs a day compared to a mean of 0.55 lbs a day in people who didn’t make it four weeks.

Here’s how the potato diet COULD have worked: some people don’t lose weight, so they quit, and other people do lose weight, so they keep going. If that happened, we would see a really successful group of people who made it to four weeks and lost a bunch of weight, and another group of dropouts who lost little or no weight. But that’s not what happened. Almost everybody who tried the diet seemed to lose about the same amount of weight per day. So something causes the dropouts to drop out, but it’s not that the diet doesn’t work for them. The diet works for pretty much everyone, at least for however long they can stick to it. But then, for unclear reasons, some people hit a wall.

You might want to know, how much weight will I lose if I don’t make it four weeks? How much weight will I lose if I start and keep going until I hit a wall? Well, it depends on how long it takes for you to hit that wall, but we can talk about what you can expect on average.

People who entered at least two weight measurements but didn’t make it four weeks lost an average of 5.5 lbs, with a median of 4.2 lbs and a maximum weight loss of 24.8 lbs.

If we pool everyone who entered at least two weight measurements, they lost an average of 7.7 lbs, with a median of 6.9 lbs and a maximum weight loss of 24.8 lbs.

So strictly speaking, if you start the diet, based on these data you should expect to lose 7.7 lbs on average. If you fully expect to make it four weeks for some reason, then you should expect to lose 10.6 lbs; and if you for some reason are sure you will NOT make it four weeks, you should still expect to lose 5.5 lbs on average.

Finally, it’s worth noting the subjective element. Just look at how happy many participants were with the diet:

I lost almost 25 lbs and have felt great throughout. I have been sleeping fine and having plenty of energy. 

Well I thought that was super fun and I’m happy to have done it. Lost about 16 pounds. … Anyway, I had a blast. I would consider doing potatoes again in the future. This is probably the thinnest I’ve been in at least 15 years or so.

Thank you for doing this. I’ve found it very valuable and think potatoes will continue to play a role in my health.

Thanks for organizing this!

Thanks for the opportunity to do this, it’s been an interesting ride, and I did lose weight. 

Hi! Thanks for doing such a great study!

I felt really good during the diet. This is the best I’ve felt in several years. My clothes fit better, I’m not as tired all the time, my back and knee has felt better than they had for the last 6 months.

I did it. One month, mostly potato. And I am really happy I came across your tweet about this crazy and kinda dumb idea for a study. Over this past month I lost pretty much exactly 10 kg / 22 lbs. It felt easy most of the time, and I feel fantastic. My goal of a BMI < 30 is still 20 kg away, but that feels achievable for the first time I can remember.

Thanks for running this experiment! It was very fun, and I wish there were more things like this going on in the world. 

Thank you so much for including me in your study! It has been a huge boon to me personally and it was nice to be able to contribute to science!

I had a good time overall with the diet, and ultimately I think the viscerally-felt revelation that an adjustment to my diet gives me far greater mental clarity will be long-term life-changing. Thanks for that.

By BMI Bracket

We can also break down these same analyses by starting BMI bracket.

None of our participants were “underweight” (BMI < 18.5) to start. Of the people who entered any data, 27 had starting BMIs between 18.5 and 25, 66 were BMI 25-30, 43 were BMI 30-35, 17 were BMI 35-40, and 7 had starting BMIs above 40. 

Retention by Starting BMI

Overall, it doesn’t seem like retention is much better or worse for people with higher or lower starting BMIs. This is a little surprising — you might expect leaner people to drop out more, since they have less to lose. Or you might expect heavier people to drop out more, because they presumably have a harder time losing weight. But we don’t really see much evidence for either.

We can also plot these variables to get a better look. We’ll adapt the colors from this uh lovely diagram by the CDC:

Again, we see pretty similar retention across groups. This plot shows the days completed, out of 28, by people in each bracket. Vertical lines are medians:

People with a BMI < 25 do seem to be more likely to drop out on the first day, but that might just be noise.  

Weight Loss

And here’s weight loss for people who completed the four weeks by BMI bracket. Again, vertical lines are medians:

As expected, people with higher starting BMIs lost more weight. We can also show this as time series: 

What is not expected, and what we find quite surprising, is that people who started the study with a BMI of less than 25 (what they call “normal weight”) often lost weight as well. And not just a little weight, a decent amount of weight. Median weight loss for BMI < 25 was actually 7.3 lbs! 

This becomes more striking if we break it out as percent body weight lost: 

A really interesting example comes from Nicky Case, who shared her experience as a, uh, a case study: 

I was already “normal BMI”, but signed up coz fighting science’s ivory tower with potato is funny

(Also the diet may help with anxiety/depression. And it’s  good to see if there’s a “floor”, i.e., it only works for “high” BMIs but not “normal” BMI)

I started 5’8″, 137lb. Already middle-low range of “normal BMI”.

I’m now on Day 19 of “try to eat only potato, but as much as you want” – and I’ve cheated on 8/19 (40%!) of the days – I’m *still* losing roughly 2.2lb/1kg a week(?!) 

…

(& from SMTM’s early data, “losing roughly 2.2lb/1kg a week” seems to be common for the volunteers so far: https://mobile.twitter.com/mold_time/status/1530527527680327680… )

(It *is* really weird, tho, that I’m getting about the same effect size even when I already started “normal” BMI *and am cheating a lot*)

All of Nicky’s feedback is great, see it in the thread.

Nicky isn’t the only example of someone who started with a low BMI and saw it go even lower. There’s also participant 89852176, who made it the full four weeks: 

I went into it not feeling like I had a lot of weight to lose (starting weight/BMI 143/21.1), but my wife and I started together at the same time, and she had more to lose. In addition, I was hoping for an improvement in my blood pressure (typically 120ish/85ish); I haven’t seen a significant change there. However, I did see significant weight loss; my ending weight/BMI (this morning, day 29) was 132.4/19.5.

Naturally we are wondering why people who are already at the bottom end of the range for “normal weight” are losing weight on this diet. Two possibilities come to mind.

One possibility is that the natural human BMI is really around 19. These days we think of 22 or 23 as pretty normal, but that seems to be the high end for hunter-gatherers. 

For example, this review says:

Walker and colleagues compiled body size and life history data for more than 20 small-scales societies. They report mean ± SD body mass indices (BMI) of 21.7 ± 2.9 for n = 21 adult female cohorts and 22.2 ± 2.7 for n = 20 male cohorts, mid-range within the WHO category for ‘normal weight’ (BMI: 18.5–24.9; WHO). … within the Hadza hunter-gatherer population, we find little evidence of overweight or obesity. BMI for both men (20.0 ± 1.7, n = 84) and women (20.3 ± 2.4, n = 108) 20 to 81 years remains essentially constant throughout adulthood and similar between sexes (Fig. 1). 

And Staffan Lindeberg, in his book Food and Western Disease, says: 

The average BMI at 40 years of age [for hunter-gatherers] has typically been around 20 kg/m2 for men and 19 kg/m2 for women. After the age of 40, the BMI for both sexes drops because muscle mass and water content decrease with age and because fat is not increasingly accumulated.

So if the potato diet is resetting your lipostat (if you’re not familiar, we describe this below) and sending your BMI towards what it would have been if you hadn’t been raised in a modern environment, maybe your BMI is headed towards the hunter-gatherer range of 19-20. 

It doesn’t seem like potatoes would send your BMI any lower, in part because there have been cultures that lived almost entirely on potatoes and they did not all drop to BMI 10 and die. For example, take this account of the Irish, from Adam Smith of all people (h/t Dwarkesh Patel):

Experience would seem to shew, that the food of the common people in Scotland is not so suitable to the human constitution as that of their neighbours of the same rank in England. But it seems to be otherwise with potatoes. The chairmen, porters, and coal-heavers in London, and those unfortunate women who live by prostitution, the strongest men and the most beautiful women perhaps in the British dominions, are said to be, the greater part of them, from the lowest rank of people in Ireland, who are generally fed with this root. No food can afford a more decisive proof of its nourishing quality, or of its being peculiarly suitable to the health of the human constitution.

Another option is that potatoes just have super weight loss properties that work no matter how much you weigh (but more on this later).

Adherence

We say “nothing but potatoes”, but the potato diet is actually a lot more permissive than all that. You get oil, spices, and drinks, and in our version of the diet, we said, “Perfect adherence isn’t necessary. If you can’t get potatoes, eat something else rather than go hungry, and pick up the potatoes again when you can.” 

People took us at our word, and many people chose to take several cheat meals or cheat days (several people mentioned loving this aspect of the diet). For each day, they reported whether or not they broke the diet, so we have an estimate of how many cheat days each person had, and we can look at that as part of this analysis.

We do want to remind you that this is self-report. Different people had different standards about what counted as breaking the diet, and some people were more rigorous about tracking this variable than others. It might be a good future project to go through all the raw data at some point and get better estimates for adherence based on the comments.

But that said, let’s take a look at them cheat days:

Only five people reported not a single cheat day. Everyone else said they broke the diet at least once. Most people cheated a few times, but a few people (36%) broke the diet for more than a week’s worth of days.

This is important because clearly the potato diet’s effects are robust to a couple’a cheat days.

We can take a better look at this with a nice scatterplot. Here we compare number of cheat days on the x-axis to weight change on the y-axis: 

You can see there’s a bit of a trend between more cheat days and less weight loss. Remember, higher numbers here are less weight loss; zero lbs is at the top. People on the left, who cheated very little, lost a whole range of weights. People on the right, who took more than 14 cheat days, tended to see much less weight loss. 

The basic correlation is only r = 0.176, and not significant. Though we do notice a weird outlier in the bottom right, and without that participant, the correlation is r = 0.303, p = .014.

One interesting thing here is that the five people who reported 0 cheat days are all tightly clustered around losing 10 lbs, so the diet does seem to maybe be the most reliable for people who don’t take cheat days. But some people who took cheat days lost a lot more than that. 

So overall we see that cheat days maybe matter a bit, but not a ton. It’s looking good for the 90% potato diet.

Heck, it’s looking good for the *40%* potato diet! Participant 68030741 broke the diet on 27 out of 28 days. (And actually didn’t mark down if he broke the diet on day 22, so maybe 28 out of 28.) He says:

I couldn’t get enough protein with only potatoes, so I supplemented with other food. Also, eating only potatoes without anything to accompany them quickly became too monotonous for me. So, I ended up getting only 40% of my calories from potatoes, but I still lost 7 lb over 4 weeks. I limited my intake of non-potatoes, but I ate potatoes ad libitum. I didn’t try to limit my daily calories; in fact the opposite, I often just wasn’t hungry enough to eat more.

There are some similar stories from other people, like participant 48507645:

I was really surprised at the results. While I cheated way more often than I wanted or anticipated, I still lost almost 10lbs. That’s with cheating almost every weekend (due to unforeseen social obligations). 

And here’s one from participant 35182564:

I also must confess, that I was not very strict with the “no dairy” rule. I took milk for my coffee (4-5 cups a day) and occasionally a small piece of butter or some spoon of plain yogurt to go with the cooked potatoes. This does not seem to have impacted the successful outcome. But it made the diet so much easier and also improved the “empty stomach” and “hungry” feelings a lot. Everything besides these “tiny” amount of dairy, I noted in the sheet.

The most extreme case study may come from Joey “No Floors” Freshwater, who shared his story on twitter. He wasn’t able to enroll in the study proper but he decided to do his own version consisting of “1-1.5lbs of potatoes a day when I could”, or about a 20% potato diet. Turns out it works just fine, for him at least. Here are some screenshots:  

So it looks like the 20% potato diet can work, at for least some people.

EASY POTATESY

Most people who made it the four weeks report the diet being anywhere between “pretty easy” and “real easy”.

(24235303) It was remarkably easy to stick to the diet.  I generally wasn’t hungry and when I was I just ate a potato.  I only had cravings for other things when I was directly looking at them, such as when I was helping to put away groceries for my family.  This seemed to require a lot less willpower than my previous successful diets.

(41297226) I lost 17 lbs in 28 days, felt very few food cravings or aversive hunger, didn’t get tired of potatoes.

(14122662) I felt mostly normal during this diet. I did often miss going out to restaurants or just having a non-potato meal, but the craving was never so strong as to be unbearable.

(63746180) Most of the time I had a good experience on the diet.  I didn’t feel cravings for other food.  Sometimes I would imagine eating out at a restaurant as a fun thing to do, but it didn’t have the same urgency as typical food cravings.  

(57747642) General Diet Thoughts: It’s really surprisingly easy. I was skeptical that I’d be able to finish the four weeks when I started, but once you get in the groove (and learn some tricks for prepping large quantities of potatoes quickly and easily) it’s extremely simple to stick with it. I basically never felt hungry or low energy.

Even some people who dropped out mentioned that it wasn’t hard for them. For example, take this report from participant 70325385: 

Overall, it was a good experience. I thought getting fewer calories would have a more detrimental effect on my mood and energy, to the point where I wouldn’t be able to function normally at all. What I noticed was mostly a ~2 point penalty to my mood and energy, which isn’t that big in the grand scheme of things but enough to be an annoyance.

On the other hand, we want to note that the potato diet was really, really hard for some people. Here are a few stories from people who stopped before completing four weeks.

(52058043) Not only is it very inconvenient to daily life and travel, it also feels pretty gross.  I feel uncomfortably full, but still wanting anything, anything at all, that isn’t potatoes.

(86547222) In short, my experience was not great. First two days I didn’t peel potatoes and my digestion went crazy. After that I started to peel potatoes, which helped but not by a lot. During those 9 days that I stuck to the diet I mostly felt apathy. The diet removed any joy associated with food from my life, and I missed that.

More speculation on some people loving it and other people hating it later.

Beyond the self-report, we can also look at people’s daily ratings of how easy they found the diet, on a 1-7 scale from 1 “hard to eat only potatoes” to 7 “lol this is so easy, I love potato”.

We averaged each person’s ease ratings over the four weeks for a mean ease rating. The mean of these ratings was 4.6 and the median was median 4.7, both of course on a 7-point scale.

It does seem like people who found the diet easier lost a bit more weight:

The correlation here is small, only r = -0.155, and not significant. This may, however, be the result of one participant who lost almost 25 lbs but seems to have hated every day of it. See him in the far bottom left? Without that guy, the correlation is r = -0.326, p = .008.

This is participant 74282722, who is also the outlier on the previous plot, with 23 cheat days out of 28 days of the diet. Perhaps this guy’s experience was not typical.

Comparison to other Diet Studies

It’s not a contest, but we think the potato diet compares pretty favorably to the rest of the literature.

Meta-analyses like this one do find that many diets cause 10-20 lbs of weight loss on average. But these studies tend to run for much longer than the study we’re reporting on today. The studies in that meta-analysis ran for 16-52 weeks (median 24 weeks) to get that 10-20 lbs of weight loss. If the potato diet went for 16-52 weeks… well that would be something wouldn’t it. At an average weight loss rate of half a pound a day, you do the math.

This meta-analysis compared interventions based on diet, exercise, and diet plus exercise found that people lost about 23.5 lbs on just a diet, 6.4 lbs on an exercise regime, and 24.2 lbs with diet plus exercise. Again this is pretty good, but these diets were all run for what they describe as “short durations”, which is 15.6 +/- 0.6 weeks.

This two-year trial from The New England Journal of Medicine compared low-fat, Mediterranean, and low-carbohydrate diets in a randomized design. All three of these diets saw only about 2 kg (4.4 lbs) weight loss at one month. This is less than the potato diet participants who dropped out before reaching four weeks, who lost an average of 5.5 lbs (median 4.2 lbs).

Maximum weight loss on these diets was at around 5 months in, when participants had lost an average of about 5 kg (11.0 lbs) in the low-fat and Mediterranean diets, and an average of about 6.5 kg (14.3 lbs) in the low-carb diet. This is about comparable to the weight loss on the potato diet, but it took five times as long.

The attrition rate for the potato diet is pretty comparable to other diet studies. That NEJM paper mentions that “common limitations of dietary trials include high attrition rates (15 to 50% within a year)”, and as a sampling from some papers we grabbed at random from Google Scholar, we see attrition rates of 49.3% in this study, 32.3% in this study, and 56.3% in this study.

Admittedly these attrition rates are over very different time scales, so it may be the case that the potato diet is a little harder to stick to than these other diets. But that seems pretty well offset by the much faster and more reliable weight loss.

We also didn’t include any of the intense measures many diet studies implement to keep their participants in line. We didn’t lock people in a metabolic ward. We didn’t control how they prepared their meals. We didn’t do portion estimation. Heck, most of our participants didn’t even stick that closely to the diet. Most of them took several cheat days! 

They still lost an average of 10.6 lbs over four weeks. Of those who made it the full four weeks, one lost zero pounds — the other 63 all lost at least 3 lbs. Of the participants who entered at least two days of weight data, two gained weight, three saw no weight change, and the other 146 lost weight. If you’re statistically inclined, the effect size for those who made it four weeks is d = 2.28. The potato diet is remarkably consistent.

​​It’s hard to estimate how much some of these other diet studies cost, but we’d guess at least tens of thousands of dollars. In comparison, our budget was $0. And we did the whole study in what, 10 weeks?

5. Effects other than Weight Loss

Ok, enough about weight loss. We were promised MORE.

The case studies did all mention weight loss, but they also mentioned other beneficial effects, the kind of thing we would love to see.

Chris Voigt reported major improvements in his bloodwork: “My cholesterol went down 67 points, my blood sugar came down and all the other blood chemistry — the iron, the calcium, the protein — all of those either stayed the same or got better.”

Andrew Taylor said, “I’m sleeping better, I no longer have joint pain from old football injuries, I’m full of energy, I have better mental clarity and focus.” 

This is pretty exciting, so we wanted to look for other effects beyond weight. To keep things simple, we just asked people to track their mood and energy every day, both on a 1-7 scale (7 is better mood and more energy).

We took a look at both variables, and there does seem to be something there. There’s a small trend for mood, from an average of 4.3 on day 1 to an average of 4.7: 

Of the people who made it four weeks, 45.3% reported a higher mood on day 28 than on day 1. An additional 34.0% reported the same mood (on a 7-point scale) on day 1 and day 28. 

And slightly more for energy, from an average of 4.1 on day 1 to an average of 4.7 on day 28:

Of the people who made it four weeks, 50.9% reported higher energy on day 28 than on day 1. An additional 37.7% reported the same level of energy (on a 7-point scale) on day 1 and day 28. 

But there’s definitely some variation — some people reported feeling VERY energetic: 

There were also some reports of more specific forms of feeling energetic, like increased fidgeting: 

(81125989) I also noticed I’m fidgeting a lot, but not sure if I was always fidget-y before, and I’m only noticing now since I’ve read about lipostats & Non-Exercise Activity Thermogenesis

(88218660) Definitely had increased fidgeting at various points.

We also did this extremely scientific poll on twitter: 

So it does look like a substantial minority experienced this, but still, a minority. 

Effects and Variables we Didn’t Ask for

We asked people to track mood and energy; but, perhaps foolishly, we didn’t ask them to track things like blood pressure and sleep. 

But despite our failure, many people chose to track additional variables anyways, and reported all kinds of other effects of the potato diet above and beyond weight loss.

Certainly many people did NOT experience these side effects. Many people just didn’t mention whether or not they experienced them, but for most of these effects, there were some people who specifically said they didn’t feel it. For example, participant 81125989, who didn’t feel anything: 

I didn’t feel any noticeably better or worse. My sleep, anxiety, & ability to focus were trash the last few weeks, but they’ve already been that way for months before anyway.

But it’s hard to tell for most of these effects, since we didn’t track them systematically. A project for next time (or for one of you!).

Anyways, here is a selection of effects other than weight loss that were mentioned at least a couple times, and/or that we found interesting.

Digestion both Good and Bad

Lots of people reported digestive changes. Some of these were good. Others were very bad.

(72706884) Other: Improved digestion. 

(89852176) almost exclusively loose stools alternating with mild constipation from day 12ish onward

(38751343) My only note is that when I ate potatoes for more than 24 hours, I had the best poops. Total no-wipers. 10/10 poops. I have IBS so it’s rare for me to have a solid bowel movement. Next time I decide to have anal sex, I’m definitely going to eat potatoes for 24 hours prior.

Before you go rushing to cram potatoes before your next bout of anal sex, beware: the potato diet gave other people diarrhea:

(68545713) I had trouble getting started with the diet because at first. I was leaving the skins on, and not using any salt or oil. I had quite extreme diarrhea in the beginning, which I attribute to the unusually high fiber. I also just don’t like potatoes, so not using any salt or oil made the actual eating of the potatoes very unpleasant for me.

After only a few days, I allowed myself salt and oil, and at about the same time I started “imperfectly peeling” the potatoes to reduce (but not eliminate) the fiber. This made the diet much easier for me.

Sleep

Several people reported better sleep, and sometimes reported sleeping more.

(72706884) Improved sleep, even with caffeine pills. I never woke up in the middle of the night, which is atypical.

(34196505) I sort of feel like I slept better. This is not consistent with how I usually feel on a calorie deficit–normally, I have a hard time sleeping.

(31664368) Good energy and sleep from a crappy baseline (~4 month old at home, just starting to get “normal” sleep)

(63173784) I needed more than usual sleep on the diet, but once I added chicken I was able to sleep more deeply

My sleep apnea symptoms disappeared, except when I had the one “normal” meal in the middle. I must be reacting to other foods. 

There may be a relationship between the amount of sleep people require on this diet and how much weight they lose — someone should look into this at some point.

Blood Pressure

Several people tracked their blood pressure, and they tended to see improvement, sometimes a lot of improvement. 

If you don’t look at BP measurements very often, here’s a quick refresher on what the different ranges mean, from the FDA:

Normal pressure is 120/80 or lower. Your blood pressure is considered high (stage 1) if it reads 130/80. Stage 2 high blood pressure is 140/90 or higher. If you get a blood pressure reading of 180/110 or higher more than once, seek medical treatment right away. A reading this high is considered “hypertensive crisis.”

Two people saw minor increases. Participant 76703005’s blood pressure went from 123/69 (day 1) to 138/82 (day 29). Similarly, participant 26650045 went from 115/76 (day 1) to 116/80 (day 24, their last day).  

But other people saw their blood pressure decline, sometimes by a lot.

(90638348) Blood pressure down, resting pulse down, pulse/ox up (data in spreadsheet) 

Looking at the spreadsheet, participant 90638348 saw their blood pressure go from 139/98 on day 3 (the first they recorded) to 122/88 on day 29. They actually have BP data up to day 32, when BP was 125/87

Participant 14558563 also tracked their blood pressure, and found it went from 164/100 (day 5) to 153/98 (day 29). They even have data up to day 35, when it was 150/102.

(68482929) I ate a LOT of seasoning and salt, but my blood pressure dropped to 111/73 (before the diet it was 139/something)

(57747642) My blood pressure went down from a pre-diet average of about 135/85 to an average now of about 128/70. So that’s interesting.

(57875769) I also checked my blood pressure a few times, although I wasn’t scientific about it so I’d consider this anecdotal, but on day two of my diet my blood pressure was 149/96 (yikes!) and my last reading on day 27 was 126/81. 

(66959098) I also took a blood pressure measurement before and after the diet, starting at 177/107 and going down to 130/80.

Not asking for blood pressure measurements was an oversight on our part, since the measurement is so standard and it’s so easy to track at home. If we run any future studies, we plan to include it; and if you try the potato diet on your own, we recommend that you track it! 

Pulse / RHR  

A few people measured their resting heart rate, and found that it dropped during their time on the potato diet.

Participant 90638348 reported their pulse (BPM) dropped from 78 (day 1) to 64 (day 29). 

Participant 14558563 reported their pulse dropped from 68 (day 5) to 56 (day 29). 

And participant 05999987 had this to say:

I noticed I often had to pee during the night, which is unusual for me. (Note that my version of potato diet was also very low sodium, mostly because bland potato was just fine with me and I figured if I got way out of Na/K balance my body would let me know, like a deer in search of a salt lick). More interesting is my resting heart rate went down by almost 10 bpm from ~63 to 54. 

Cholesterol

A few people got more comprehensive blood work done, and the changes they saw over the course of the diet were generally positive. 

Participant 95730133 had this to say in his closing remarks: 

As promised, here’s the results of my blood work! Taken on the first day (5/31) and last day (6/27) of my potato diet. Note the second test was also fasted though it isn’t marked.

Summary:

Total cholesterol dropped from a high 242 mg/dL to a healthy 183 mg/dL.

LDL cholesterol improved from a high 148 mg/dL to a still high 124 mg/dL (0-99 is the target range).

All other levels remained healthy and in the target ranges.

Another participant (23300304) sent us his full blood test results. Like the guy above, 23300304 saw his total cholesterol drop, from 4.5 mmol/L to 3.1 mmol/L (about 174 mg/dL to 120 mg/L in the other units). He also saw his LDL cholesterol drop from 3.0 mmol/L to 1.4 mmol/L (116 mg/L to 54 mg/L). However, his triglycerides went up, from 0.65 mmol/L to 1.79 mmol/L.

Hypomania

When we tried this diet, we experienced some pretty hardcore hypomania:

This makes sense for us because we are mad scientists. But would “normal” people experience the super-wiring effects of potatoes too? Apparently yes, though certainly not everyone.

Participant 68545713 reported:

Energetically and mentally, I felt very energetic on the diet in a “hectic” kind of way. Not bad at all for me, that’s my preferred state. I tend to think of my mental clarity as being about a) how many trains of thought I can have going at once and b) how often I lose a train of thought to a blank mind. On potatoes, I had all ~3 trains running, and I rarely lost a thought. (That is quite unusual for me, and strikes me as very unlikely to be a coincidence.) … I’d classify the energy I get from a potatoes-only diet as “frantic”, or “hectic”, or “excited”.

Participant 15106191 gave these notes:

(Day 5) Energy boost kicked in today. Feel half my age

(Day 6) Potato energy going strong. Feel like Irish Superman

(Day 15) Almost too much energy, hard to sit down at a computer and work, took a break to play basketball 

And participant 02142044 described: 

[At] one point, I was feeling a mild euphoria, and then it just stopped … I felt a sort of euphoria/hypomania that lasted from day 17 to day 20, and I’m unsure how to reproduce it

Certainly not everyone saw this effect of the potatoes. Participant 90638348 said:

Never saw the manic energy described by other folks. I was sorta looking forward to that.

Migraines 

Only one person mentioned their migraines, but most participants probably don’t have migraines to begin with, so we found this interesting. This was participant 35182564, who said:

My frequent migraines improved during the diet. I could also go much longer without food than before and the blood sugar ups and downs were less pronounced, which is probably why the migraine is better. I am very happy about that.

Acne

Similarly, one person mentioned a serious improvement in their skin. Participant 36634531: 

One unexpected consequence is that my skin is way clearer.  I usually have a lot of redness in my face and am acne-prone.  My skin has been way less red and acne has been infrequent which makes me wonder if I have a food allergy.  If relevant for genetic reasons:  I am of Jewish and English/Irish descent.

Libido

Two people mentioned libido issues; participant 95730133:

My libido was down a good bit this month, which I’ve seen during weight loss periods before.

…and participant 70325385

The diet had a fairly large effect on my energy and mood most days, and greatly decreased libido starting almost immediately.

Most people didn’t report this effect; but also no one mentioned the potato diet making them extra horny. 

Fear and Grief???

One of the strangest effects that some people reported was an increase in intense feelings of fear and grief. For example, participant 95730133, who said:

I had 2-3 days with bad anxiety, which is super uncommon for me and represents a big chunk of the days I’ve ever felt anxious. May have had something to do with the rapid weight loss / potatoes.

We also saw some clear anecdotes about this on twitter: 

Chairman Birb Bernanke also discussed this a bit more in a retrospective post on her substack:

Like I said above, potato diet is fucking weird. I mention this and the above because towards the end of the third week, I found myself crying every day. I was having actual meltdowns… five days in a row. 

I am not talking “oh I am so sad, let a single tear roll down my cheek while I stare out of a window on a rainy day” levels of gloom and general depression. I am talking “at one point I couldn’t fold some of my laundry in a way that was acceptable to me, and this made me think I should kill myself, so I started crying”. 

Is this a really dark to drop in the middle of a sort of lighthearted post about potato diet? Yes. I am sorry if you are uncomfortable reading it. Personally, I think I have a responsibility to talk about it, because the mentally weird aspect of this diet cannot be stressed enough.

If you experience this kind of side effect, we recommend you dial back or discontinue the diet. As Birb put it:

To anyone who wants to do this diet, or is considering it after the benefits I described above: I encourage you to do it, but please be extra cautious that your mental state might be altered and that you are not necessarily in your right mind.

Muscle / Exercise

Finally, let’s talk about the topic on everyone’s mind: getting swole, and staying that way.

When we opened signups, many people asked if you’d be able to get enough protein on an all-potato diet. Potatoes do have some protein, and more than their reputation would lead you to believe (3-5 g in a medium potato), but it’s true that 20 potatoes a day won’t give you as much protein as many people think you need. 

This is where we reveal that this community trial is not actually the first-ever study of an all-potato diet. There are a few very small, very old studies, and they’re pretty illuminating on the subject of potato fitness. Stephan Guyenet explains:

Starting nearly a century ago, a few researchers decided to feed volunteers potato-only diets to achieve various research objectives. The first such experiment was carried out by a Dr. M. Hindhede and published in 1913 (described in 15). Hindhede’s goal was to explore the lower limit of the human protein requirement and the biological quality of potato protein. He fed three healthy adult men almost nothing but potatoes and margarine for 309 days (margarine was not made from hydrogenated seed oils at the time), all while making them do progressively more demanding physical labor. They apparently remained in good physical condition. Here’s a description of one of his volunteers, a Mr. Madsen, from another book (described in 16; thanks to Matt Metzgar):

“In order to test whether it was possible to perform heavy work on a strict potato diet, Mr. Madsen took a place as a farm laborer… His physical condition was excellent. In his book, Dr. Hindhede shows a photograph of Mr. Madsen taken on December 21st, 1912, after he had lived for almost a year entirely on potatoes. This photograph shows a strong, solid, athletic-looking figure, all of whose muscles are well-developed, and without excess fat. …Hindhede had him examined by five physicians, including a diagnostician, a specialist in gastric and intestinal diseases, an X-ray specialist, and a blood specialist. They all pronounced him to be in a state of perfect health.”

Dr. Hindhede discovered that potato protein is high quality, providing all essential amino acids and high digestibility. Potato protein alone is sufficient to sustain an athletic man (although that doesn’t make it optimal). A subsequent potato feeding study published in 1927 confirmed this finding (17). Two volunteers, a man and a woman, ate almost nothing but potatoes with a bit of lard and butter for 5.5 months. The man was an athlete but the woman was sedentary. Body weight and nitrogen balance (reflecting protein gain/loss from the body) remained constant throughout the experiment, indicating that their muscles were not atrophying at any appreciable rate, and they were probably not putting on fat. The investigators remarked:

“The digestion was excellent throughout the experiment and both subjects felt very well. They did not tire of the uniform potato diet and there was no craving for change.”

So previous all-potato diets didn’t lead to serious atrophy; it seems like people can maintain muscle just fine on a potato diet, and maybe even build muscle. Despite being relatively low in protein, that protein may be exceptionally available or otherwise of unusually high quality.

Empirically, participants in our potato study seemed to lose mostly fat, not muscle. Participant 10157137 used a Fitbit Aria scale to measure fat %, which went from 17.3% (day 1) to 16.5% (day 28). And they were not alone: 

(57875769) I lost nearly 17 pounds, and if the body composition on my scale is to be believed, roughly 75% of that was fat. 

(46804417) In total I lost 12.5lb (5.7kg) and 4.3% (33%->28.7%) body fat. I measured the fat % using a FitBit Aria 2 scale. I found it impressive that almost all the weight I lost was fat, usually when I diet I lose some fat but close to maybe half of the total?

Maybe you don’t trust these home scales, and you know what, fair enough. But these numbers are backed up with athletic performance, which indicates no noticeable muscle loss: 

(41297226) Weightlifting: I’ve been lifting off an on the last couple months. Went from deadlift/squat/bench of 155/165/135 on April 29th (day -5 pre-diet) to 160/145/125 on May 16th (day 13, first time lifting during diet) to 175/150/140 (day 21). I’d say: inconclusive, but doesn’t seem like I was held back from improvement by potatoes (+ taking 4g of BCAAs post workout)

(14122662) In general, I was shocked by the amount of weight I lost, especially since I started out slim and didn’t have much weight to lose in the first place. I had to actively make sure I was eating enough each day so that I wouldn’t lose even more weight. That said, I felt fine throughout the diet and stayed physically active by rock climbing, hiking, and playing kickball and tennis. My health was never a big concern for me.

(01772895) I went on several pretty intense road/mountain bike rides and kept up while feeling good over the course of the diet.

(05999987) I stuck with my usual level of physical activity which is at least 5 miles of walking a day, with some plyometrics. On the few occasions I did do some more intensive activities (a hike with a long, steep uphill portion) or jogging I felt more muscularly tired than usual, though in general I had average for me, or slightly above average energy.

(74872365) I felt unable/unwilling to lift weights during it. I was lifting 3x a week beforehand, and tried near the beginning to workout a couple times but started feeling kinds of joint soreness I wasn’t used to (assuming because of impaired recovery from previous workout). I tried to give it a few more days rest and just suddenly felt very much like not exercising… so I hardly lifted at all for the rest of it. But after the diet was over (a few weeks after it, what with moving and stuff) I got back into gym, got going again at reduced weights, and in two weeks matched or exceeded previous personal bests on most lifts (but haven’t gotten back to previous bench press best). I overall feel very positive about the way in which I was able to resume working out and hitting PRs after it was over, it wasn’t an overall bad thing for my lifting in the grand scheme.

On the other hand, not everyone had sustained athletic performance on the potato diet. For example, participant 57747642 said: 

One difficulty for me was keeping up my running volume on the diet. Pre-diet I ran ~20 miles a week. During the diet I found longer runs to be extremely tiring–I think I was just in too much of a caloric deficit to have much glycogen available. I started cheating by drinking a bottle of gatorade before my longer runs and that seemed to fix the issue. But I still only averaged about 8 miles a week of running which was quite a step down.

(15106191; Day 14) Bench press went down today, likely losing muscle along with the fat, either because of the low protein of potatoes or just the calorie deficit

(34196505) I lift weights at the gym a few times a week, and even on days when I made a point of eating a ton, I felt more fatigued and had a hard time lifting my goal weight. Physical activity seemed harder in general. This is consistent with how I usually feel about a calorie deficit.

If you’re training for a marathon that’s four weeks away, don’t start now. But for most of us, it’s clear that four weeks of the potato diet doesn’t cause serious atrophy or muscle loss.

6. Why do Some People find the Diet Easy and Others Don’t? 

Some people find the diet comically easy, while other people hit a wall at some point and are suddenly unable to eat another potato. We’d like to know why. 

It’s worth distinguishing between two things; or that is to say, we think there are two ways to lose weight on the potato diet.

First, you can grit your teeth and force yourself to eat nothing but starchy tubers while fighting back your desire to eat literally anything else. A few people who made it the full four weeks seem to have had this experience. For example, participant 83122914:

It was an interesting experience, but it didn’t feel like any kind of magic bullet for long-term weight loss. I initially ate mostly mashed potatoes, but over time I found myself losing the desire to eat them. I craved meat, salad, etc. … I’ve had similar weight loss results in the past with a low-carb diet. 

But most people lost weight the other way: after a day or two of eating potatoes, their appetite waned, they didn’t want anything else, and they began to steadily lose weight.

This is the interesting part. To make this easier to talk about, let’s call it entering “potato mode”, or “potatosis”. Actually, Greek for potato is “patata”, should it be “patataosis”? 

Also worth noting that it’s not like the potato diet was just easy for some people and hard for others. More like, almost everyone found it easy at first. Some people found it easy for days or weeks and then suddenly hit a wall. So the question may be more like, why do some people hit a wall at three days, others at three weeks, and others apparently not at all? 

Demographics

It’s possible that the difference between the people who found the diet easy and the people who hit a wall will be something easy to notice, maybe basic demographic variables like race and sex. Let’s see:

The group of participants who provided us any data were mostly male (any way you slice it), mostly white, and mostly from the US.

But overall, basic demographics don’t seem to track onto who made it four weeks and who ended the study early. People who made it four weeks were slightly older, more likely to be from the US, and less likely to be white, but none of these differences are very big.

The only difference that jumps out is by sex. About 20% of the people who got to the point of recording data were female, compared to only about 10% of the people who made it four weeks.

We’re not sure why, or if this is even a real result. With so few female participants to start with, this could just be random noise. 

Participants who are XY did report the diet being a little easier, with a mean ease rating of 4.4/7, compared to 4.2/7 for XX participants, but this is not significant (p = 0.530). 

We also noticed that XY participants did complete slightly more days overall, but it’s not clear if this is robust. Looking at the plotted data, it doesn’t seem like a huge difference: 

It’s notable that our three big case studies (Chris Voigt, Andrew Taylor, and Penn Jilette) were all XY. We also did look at Brian & Jessica Krock, though, and Jessica Krock is XX. She made it pretty far on an all-potato diet, but she also seems to have found it much, much harder than most people do:

The first day of potatoes sucked. I seriously contemplated quitting during the FIRST day. After eating my first round of potatoes, I literally walked from our apartment to a grocery store to look at the extra cheesy hot-and-ready pizza I thought I needed. I gazed at the pizza and walked around the store looking for something to eat. Luckily, I was able to keep it together and walk out of the store and back home to my pantry full of potatoes.

I’m not trying to be dramatic, but it was seriously one of the hardest things I’ve done in my life. It took more will power than I thought either of us had.

But with such a small number of XX participants, it’s hard to be sure.

That said, 20% (6 out of 30) of XX participants made it four weeks. If the potato diet only works for one out of every five people with two X chromosomes, that’s still pretty good.

We do wonder if this is a real effect, and if so, why it happens. It would be good if future studies had more XX participants. 

Having lots of trans participants would also help us tell if the cause is more hormonal or more chromosomal. In this study, there aren’t enough people whose chromosomes and hormones don’t “match” to actually disentangle any effects.

Oil

Some people seemed to have an easier time, or see better weight loss, when they used less oil.

For our own part, one of us was fine for the first two weeks on a relaxed all-potato diet with olive oil, but didn’t see any weight loss until switching to a no-oil version for the last two weeks, when they lost 10 lbs. 

Participant 68482929 did some analysis of his own on this question: 

The amount of olive oil I consumed had a noticeable effect on how much weight I lost:

image.png

The main thing I craved on the diet was more olive oil. If I ate 10 tbsp / day, that felt about right (and my stool was normal and I gained a bit of weight on those days). The more I cut the oil, the more I had intestinal distress, and the more weight I lost.

Here’s that image: 

Participant 88218660 mentioned something similar: 

third week – started making air fryer fries at home with < 1 Tbsp of oil and eating pretty much only these. Also allowed myself to have ketchup – I’d estimate an upper bound of 200 calories per day of ketchup, but I expect it was less than that. Stopped losing weight. Very unclear if this is a natural plateau or an actual effect of ketchup. Cravings came back in force, as did normal hunger feeling.

Final day – switched back to mashed potatoes with no oil. Hunger was gone again, cravings were dampened, but didn’t immediately lose any more weight.

It’s not clear if this was the oil or the ketchup (or something else) but they definitely seem to have dropped out of potato mode for some reason. We reached out to participant 88218660 for clarification and he told us that he used olive oil at home. 

Despite these stories, many people used lots of oil throughout the diet and still lost weight. This suggests it’s not that all oil is bad and inhibits the potato diet. More likely, it’s that 1) some kinds of oil (e.g. olive oil vs canola oil) inhibit potato mode more than others, 2) certain batches / sources of the same oil (two different brands of canola oil or something) inhibit potato mode for some reason, 3) some people respond to oil differently because of genetics or microbiome or something, or probably 4) some combination of the above. Or it could just be noise, this isn’t strong evidence yet.

Nicky Case also recently did a regression analysis of her own data over 40 days, and found a strong effect of olive oil. But it looks like it was in the opposite direction — for her, more olive oil was associated with more weight loss. Check out the analysis in her twitter thread:

It’s sort of not surprising that all these anecdotes reference olive oil, since we recommended that people should probably use olive oil if they use oil at all. But it’s still kind of interesting. Recommending olive oil might have limited the amount of information we’ll be able to get out of these data! A few people did mention they did very well on Five Guys fries, which are fried in peanut oil… Five Guys, talk to us. 

Some people did keep detailed notes of their oil consumption, so it’s possible that a clear answer to this question is hiding somewhere in the data. But it’s also possible that we’d need to run a controlled experiment to figure it out, and we may do that at some point (unless one of you gets to it first?).

Salt / Sodium

Salt intake might also help explain why some people had trouble with this diet. 

We didn’t ask people to limit salt intake, but some people may have been keeping their intake down anyways, and that may have made the diet harder than necessary. Even if they weren’t trying to limit how much salt they ate, they may still not have been getting enough. Potatoes by themselves are a naturally low-sodium food. 

For example, consider the experience of participant 57875769:

Probably my biggest piece of advice is to use plenty of salt. Depending on the nutrition labels, potatoes have zero sodium or an extremely low amount. It seems hard to get the recommended amount of sodium (and I’ve seen some heterodox sources that say the recommendations should be even twice as high as they are) without adding salt to potatoes. A few days I felt kind of light headed or unfocused and I’d finding adding a little bit of salt to a glass of water (under the threshold where I could taste it) would often improve things pretty quickly.

Or this participant on twitter: 

Some people also mentioned craving pickled things, which could be the manifestation of a salt craving:

(01772895) Interestingly toward the end, my main cravings were actually for pickled vegetables for some reason.

Of course, we don’t know for sure if the people who dropped out early WEREN’T getting enough salt. But if some people were avoiding salt this could explain some of the difference.

Health

Another possibility is that finding the potato diet difficult can be an early sign of health issues.

Potatoes are high in potassium, and the kidneys need to do a certain amount of work to clear all that potassium from your system. They’re also high in certain toxins. A healthy body under no extra stress is equipped to handle these toxins no problem. But if your health is compromised, it might be another story. 

If you eat one potato, your body will be able to deal with the extra potassium and the low levels of plant toxins. If you eat nothing but potatoes and you have reasonably healthy kidneys, again your body will be able to handle it. But if you eat nothing but potatoes and you have poor kidney health, at some point your poor kidneys may not be able to handle all the extra potassium, potato toxins, and other junk. This will make you start to feel terrible, and may explain why some people did fine on the potato diet for a long time and then suddenly started feeling terrible.

Kidney function seems like the simplest case, but other kinds of hidden health issues could also give your body trouble.

The clearest example comes from Alex Beal (who gave us permission to use his case as an example). He was one of our earliest participants in the potato diet, and also one of the first to drop out of the study. He started tweeting about his experience, did ok on the first meal, but soon found himself feeling awful and totally unable to stand potatoes. He published a log of his experiences here, where he says: 

I’ve decided to drop out of the study after less than 48 hours. This diet kicked my ass.  

Beal stopped the diet on May 1st. A few days later, he found out he had prediabetes:

This maybe explains why he had such unusual trouble with the potato diet (remember, 90% of people who entered at least one day of data made it more than two days, and 40% made it all the way to day 28). Beal has a (mild) metabolic disorder he didn’t know about when he started, and it’s pretty reasonable to suspect that this may have limited his ability to deal with all these potatoes.

We discussed this with Beal and he agrees it’s plausible. “In a study population of obese folks,” he says, “I do worry undiagnosed diabetes or prediabetes is a risk. It’s very common for it to go undiagnosed.” This is similar to something JP Callaghan mentioned, where he said, “There are tons of people walking around with their kidneys at like 50% or worse who don’t even know it.”

Beal did mention that his kidney numbers came back ok, so it’s probably not literally potassium clearance in his case (though who knows).

One strike against this explanation is that younger people generally have better kidney function, so if this were why people are dropping out of the study, you’d expect to see many fewer dropouts among younger people, which we don’t see. But for what it’s worth, Alex Beal is pretty young and he had undiagnosed prediabetes before signing up for the study. It’s possible that we recruited a sample that has disproportionately high numbers of young people with undiagnosed renal and/or metabolic disorders.

In any case, finding the potato diet really hard may be an early warning sign for kidney issues and/or diabetes, possibly because the high levels of potassium put a strain on your kidneys that you wouldn’t normally experience, so it might reveal problems you wouldn’t normally notice. So the potato diet may be a useful at-home diagnostic tool.

If you had a hard time with the potato diet, especially if you were only able to make it a few days, talk to your doctor about checking for kidney function and prediabetes.

Whatever you find out, please let us know, that’s important data.

Peels

A related issue comes from potato peels.

A number of people mentioned that peeling the potatoes made the diet noticeably easier:

(02142044) The diet was a bit tough at the beginning, probably because I didn’t peel them. 

(68545713) After only a few days, I allowed myself salt and oil, and at about the same time I started “imperfectly peeling” the potatoes to reduce (but not eliminate) the fiber. This made the diet much easier for me.

(86547222) First two days I didn’t peel potatoes and my digestion went crazy. After that I started to peel potatoes, which helped but not by a lot.

This matches our experience. On the potato diet, there was a point at which the peels started getting disgusting — but without the peel, potatoes continued to be delicious. We were very pro-peels starting out, but by about halfway through, we started peeling them and that made a clear difference.

This is interesting because it certainly goes against common wisdom about the peels — that they’re especially nutritious, that they’re good for you, and so on. It’s true they’re high in fiber, and it may be fine if you are eating only like, four or five potatoes now and then. But as Stephan Guyenet points out:

Peel [potatoes] before eating if you rely on them as a staple food … Potato peels are nutritious but contain toxins.

Again, your body can handle most vegetable toxins in small doses. But if you are eating a lot, at some point they might get to the point where it’s a problem.

So it could certainly be that past a certain point, eating the peels will become difficult for some people. Or it could be that the peels are generally fine if you’re healthy, but they pose a problem for people with undiagnosed poor kidney function. There could easily be a peels * kidney interaction.

It could also just be fiber. Lots of people reported digestive issues, and the peels are especially high in dietary fiber. 

So it’s possible that some people who dropped out early could have made it further if they started peeling their potatoes. If you’re having trouble on the diet, we definitely recommend ditching the peels.

It’s Random

Like we mentioned, potatoes contain toxins, and some potatoes contain more toxins than others. For example, levels of the toxin solanine increase when potatoes are improperly stored, or exposed to too much sunlight, and green potatoes tend to have more solanine.

Most bags of potatoes are fine, but maybe one day you go to the grocery store and just happen to get a bag of greener-than-usual potatoes, which make you feel sick, and since you’re being careful, prompt you to end the diet early. From your perspective you can’t tell why you suddenly got sick, but from a god’s-eye-view, it was the bad batch of potatoes. So maybe random chance is what’s causing some people to hit a wall.

(Just avoiding green potatoes wouldn’t totally fix the problem, because potatoes can be high in toxins without being green. But definitely do avoid green potatoes.)

If this were the case, it would look pretty random who drops out. It does look pretty random who drops out. So maybe the dropouts are from some kind of random factor like this!

7. Why the Heck Does the Potato Diet Work

The human body has a lipostat that regulates body weight, and the lipostat has a setpoint, a weight that it wants to maintain. For the sake of an example, let’s say it wants to maintain a BMI of 23. The lipostat can detect how much fat is stored and takes action to drive body fatness to the set point of BMI = 23. If your body’s BMI is below the setpoint, the lipostat will drive you to eat more, exercise less, sleep more, and store more of what you eat as fat. If your body’s BMI is above the setpoint, the lipostat will drive you to eat less, move and fidget more, and store less of the food you eat as fat.

People become obese because something has gone wrong with the lipostat — for some reason it is defending a set point above BMI 30, and all the regulatory systems of the body are working together to push body weight to that level and keep it there (for more information, see here).

It seems clear to us that something about the potato diet lowers your lipostat set point, and weight loss kicks in because the lipostat starts to defend that new, lower weight.

When you run a normal calorie deficit (don’t eat as many calories as you need), you get sluggish, you lack energy, you get hungry, and you have a hard time exercising. This is because your body wants to defend its weight at the current set point, whatever that point is, and will work really hard to keep you from getting lighter.

But when you are heavier than your current set point, the body pulls out all the stops to help you lose weight and drop to the set point. You feel more energetic, you fidget to burn extra calories, your body temperature goes up, you stop feeling hungry, and so on. In line with this, people in potato mode reported being very energetic, having hypomania, fidgeting all the time, and having no trouble exercising. This is exactly what we’d predict if your lipostat set point suddenly went down.

In addition, there are two special points that strongly support the idea that the potato diet lowers your lipostat set point. 

First, some people keep losing weight after stopping the diet. We think this means that the lipostat set point dropped faster than weight loss was able to follow, and it took a few days after the diet was over for BMI to catch up. If the diet just worked on caloric restriction, then you would expect people to start gaining weight again after stopping. But that’s not the case, or at least, not always the case.

(36634531) My weight is still holding steady after resumption of a typical diet.  Are you guys going to ping the participants in X months to see if we return to baseline? 

(57875769) Since stopping my weight has stayed pretty flat (I was 215.3 lbs this morning and I ended the diet at 215.2, and I was traveling for a few days which usually causes me to gain weight) and I find that I have a much smaller appetite than I used to. I’m having to re-learn how much food I should serve myself or order at each meal because I’m used to eating much more. 

This is just suggestive for now, but we’ll know more in 6 months when we do the first followup. 

But the biggest sign that the potato diet lowers your lipostat set point is the overwhelmingly common experience of how the potato diet makes hunger feel entirely different.

(36634531) My appetite did eventually tank.  I was down to one meal a day.  I don’t know if I was just full all the time or if my stomach shrunk or what.  I was never feeling hungry throughout the diet.

(68545713) [I] felt less desperate than before-potatoes when I did get hungry. It was wonderful.

(29550957) Subjective feeling is definitely that I could get hungry, but it was not an urgent problem. Completely different from my usual modus operandi of gravitating in the direction of food whenever slightly hungry.

(10010108) I simply was not hungry in the mornings. Once I did start eating, I was starving every 1-2 hours. Out of habit, I do not eat after 8 pm. Sometimes we would have dinner at 7 due to scheduling, and I would be stomach growling hungry at bedtime, between 10-12. I was not going to get up and eat, so I drank water and slept. The hunger just wasn’t there in the mornings though. 

(81125989) My sense of hunger was anomalous: some days I’d eat less than 1000 calories and feel totally fine, some days I’d get a sudden sharp pang of hunger right after a hefty meal. And on my cheat days, even when I ate to satiety, I ate a lot less than I did pre-potato diet.

(74872365) I recall feeling like hunger exists in two distinct modes, and potato diet worked helped switch one off while downregulating the other: there’s the “need to feel full and need blood sugar” hunger and the “pleasure reward hunger.” It was like when I finished a mashed potato dinner the first hunger was satiated fully but I still would have eaten a whole pint of ice cream for pleasure if I was allowed to. I still kind of wanted to eat for more pleasure, but the pleasure based eating was “deactivated” from controlling my decision, and the potatoes weren’t hitting that pleasure center. Hence I only ate up to the level of the first hunger metric, the more “physical” one, and that level was downregulated of course. During cheat days (which were all around dinner times I think), the moment I started eating non-potato, I got insanely outlandishly hungry and ate surprising amounts of food the rest of the evening. It was like I would eat a bunch and then suddenly feel empty an hour later.

 

(68030741) I limited my intake of non-potatoes, but I ate potatoes ad libitum.  I didn’t try to limit my daily calories; in fact the opposite, I often just wasn’t hungry enough to eat more.

(1772895) Toward the end of the diet, I found it difficult to eat enough potatoes. I’d be a bit tired and hungry, but the effort of cooking them and eating them seemed too much to bother with. This was an interesting experience, and gave me some empathy for a few of my friends who have a hard time keeping weight on, even with an unrestricted diet. When they’ve described themselves as sometimes being ‘too lazy to eat’ in the past, I basically found that unimaginable, as I don’t think I could ever be too lazy to eat cake, for example. However, if the reward I got from eating cake was similar to the reward I get from eating potatoes, I guess that’s how I’d feel.

What’s interesting though is that I wasn’t feeling tired and hungry and craving some other food — I just didn’t feel like eating. Maybe this is something to do with the stuff Pen Gillette mentioned about eating habits fading. Interestingly toward the end, my main cravings were actually for pickled vegetables for some reason.

(77742719) I did get more tired throughout, and my appetite actually continually decreased. Had to remind myself to eat quite often and actually made a schedule. On this last day, I had only one meal of potatoes, 500 kcal.

(90638348) Was not ever resentful or hungry, always felt “full”

(88218660) First week – no oil, pretty much all mashed, non-organic russets with cajun seasoning and hot sauce. Almost immediately I could tell my cravings were significantly dampened (though not gone, especially if I was looking at tasty food) and that the normal feeling of hunger was entirely gone for me – what was left was a feeling of being almost faint and feeling not great when I went too long without eating. Took a lot of adjusting to.

(57875769) I feel full sooner than I used to, and I feel like there is a much richer variety of sensations that influence whether I want to eat more food. I remember some people advocating that to maintain a healthy weight you just need to learn to listen to my body, which is sort of what this feels like. Perhaps the people giving that advice were always thin and so listening to their body was never hard. I’ve started feeling signals I don’t remember feeling before I started the diet. It’s almost as if the volume from some things (e.g. a hyper-palatable diet) drowned out and deafened me to all the signals I was supposed to listen to. Now I feel like I’m hearing these again.

(76011343) throughout I had a ton more energy, better mood, weird hunger effect that you guys have documented (didn’t feel hungry and had to force self to eat)

As you can probably tell, this experience was extremely common. But we should note that it wasn’t universal, even among people who lost a lot of weight. Participant 99479977 lost 22lbs but specifically mentioned no appetite/hunger effect: 

I’ve seen a lot of people mentioning how the diet changed their perception of hunger. For me at least that didn’t change. What I did notice though is that I become sated much quicker. Today I packed myself four medium size roasted potatoes for lunch during uni, and I felt sated after just three of them.

And see also this report from participant 34196505:

It wasn’t like some hunger switch flipped off in my brain after a day or three of nothing but baked potatoes–I still got hungry, and it felt similar to normal hunger. I saw people on twitter saying they were having a hard time reaching 1,000 calories a day. Can’t relate.

People did eat very few calories on this diet. Most people didn’t track calories very closely (another benefit of the diet — no calorie counting!) but some people chose to record how much they were eating. The people who recorded calories (self-report, so grain of salt here) generally reported eating very little.

For example, participant 68030741 kept super detailed notes on calorie consumption and should be the starting point for anyone who wants to dive deeper into this question. He reports eating as little as 756 calories in a given day, and never more than 1740. 

Participant 71309629 never reported eating more than 1556 kcal, and ate as little as 307 kcal one day.

Participant 07644625 has “been tracking [calories] for 4035 days … hard to stop now” and reported eating as little as 1172 kcal in a day — but also often ate more than 2000.

Participant 05999987 also said:

As for ease of diet, it was quite easy to feel full, without eating very many calories at all. This worried me the first week, even on days when I supplemented the potatoes with salmon I never ate even  1300 calories a day. In fact, I averaged 921 calories per day. 

This is consistent with the reduced appetite. But it is NOT an explanation any more than “the bullet” is a good explanation for “who killed the mayor?” Something about the potato diet lowered people’s lipostat set point, which reduced their appetite, which yes made them eat fewer calories, which was part of what led them to lose weight. Yes, “fewer kcal/day” is somewhere in the causal chain. No, it is not an explanation.

But we’re bored of trying to explain this one, so we’re going to let the cat do it:

Alternately, if you prefer your arguments to come from bipeds:

Theories 

We’ve previously written about how we don’t believe in definitive experiments, so we don’t think that the potato diet will be the silver bullet for or against any particular theory. In general, most theories predict the potato diet should cause weight loss, so the potato diet does not do much to distinguish between them.

But that’s ok, this study was not designed to help distinguish between different theories of the obesity epidemic — it was designed to see if the potato diet works under realistic conditions, and to get a rough sense of what percent of people it works for. Now that we have that, future studies can use the potato diet as a “model diet” to start pitting theories against one another. Won’t that be fun. 

Even so, the data from this first study does tell us a little bit about different theories. Compared to other diet studies, the potato diet has the benefit of being super controlled — it’s a clear baseline of potato, with few interfering factors. So let’s take a look.

Something special about potatoes?

One thing we need to address right off the bat is the possibility that potatoes cure obesity for some reason totally unrelated to the obesity epidemic.

For example: cocaine makes you lose weight. But the obesity epidemic didn’t happen because everyone was on cocaine for all of history, which kept them skinny, and then in the 20th century people started forgetting to take their cocaine, and we all gained 40 lbs. It’s just that cocaine has strong weight loss effects totally unrelated to whatever caused the obesity epidemic. 

Similarly, it’s possible that potatoes are just a potent weight-loss drug for reasons totally unrelated to the increase in obesity since circa 1970. There are a few things that make this seem plausible.

For starters, Staffan Lindeberg, in his book Food and Western Disease, has a whole section on how maybe humans were built to eat roots and tubers: 

Increasing evidence suggests that large starchy underground storage organs (roots, tubers, bulbs and corms), which plants form in dry climates, were staple foods 1–2 million years ago. There are at least three arguments in favour of this notion. Firstly, in contrast to most other animals including non-human primates, humans have an exceptional capacity to produce salivary amylase in order to begin hydrolysis of starch in the mouth. The underlying change in copy number of the gene coding for salivary amylase may have occurred approximately 1 million years ago. … Secondly, roots often need to be prepared under high temperature in order for its starch to be available for digestion and for its bioactive or toxic substances to be neutralised. There are many indications of Palaeolithic humans using fire for cooking, and one of the most common cooking methods for plant foods was probably the so-called earth oven, where food wrapped in large leaves is placed in a covered pit with hot stones or glowing coals. Thirdly, human tooth morphology, including incisal orientation, seems to be well designed for chewing root vegetables. … Our bipedal ancestors were apparently less efficient hunters than many carnivorous animals and less efficient fruit-foragers than the arboreal primates. In order to increase the caloric yield per workload (‘optimal foraging strategy’), root vegetables may often have been an optimal dietary choice. An illustrative example is the Machiguenga tribe of the Amazon, among whom one woman can dig up enough root vegetables in one hour to feed 25 adults for one day. The excellent health status among this and other starch-eating ethnic groups, including our own study population in Papua New Guinea (see Section 4.1), contradicts the popular notion that such foods are a cause of obesity and type 2 diabetes.

If we really are built to eat tubers above and beyond all other foods, this might explain why the potato diet lowers your lipostat set point to hunter-gatherer levels.

There’s also some evidence that potato protease inhibitor II suppresses appetite and reduces food intake, though these studies don’t seem to be especially targeted — it looks like they basically just gave people potato extract. 

We don’t think the evidence is all that strong, but it certainly seems possible that potatoes just suppress appetite and make you lose weight.

We’ll know more when we get the six-month followup results. If potatoes just suppress your appetite during the time you’re eating them, then once you stop eating them, you should gain most of the weight back. But if potatoes are doing something more profound, and resetting your lipostat or whatever (however they do that), then weight loss should be at least somewhat sustained by six months out. For what it’s worth, this is what we see in the case studies, like Penn Jillette and Andrew Taylor, who seem to have had little trouble keeping the weight off.

It’s possible of course that BOTH are true, that potatoes both suppress your appetite in the short term and somehow reset your lipostat in the long term. In fact, the combination of these effects would be a pretty good explanation for why the potato diet is so unusually powerful. But we’ll have to wait and see.

But assuming for a moment that potatoes are NOT a superpotent weight-loss drug for some reason, what would this tell us about other theories? 

Calorie-Counting, Willpower, and other Traditional Diets

No.

(34459757) Pretty easy as far as diets go, basically never felt hungry. Previously I’ve successfully lost 25 lbs via just calorie restriction (mostly by eating box mac and cheese and other prepackaged things with easy calorie counts), and potatoes were definitely easier and I lost weight at the same speed. 

(66959098) It felt pretty easy.  I have tried simple CICO diets before where I simply reduce portion sizes and maintain a calorie deficit, which were incredibly hard to follow through and caused me to think about food all of the time. This had no such effect, no strong hunger, no strong cravings. I am happy with the results from just three weeks.

(99479977) I have tried various diets before, but restricting calories while eating whatever I like left me hungry, which lead to overeating and actually gaining more weight. The potato diet kept me sated, allows for just enough variety (especially through condiments) to keep me engaged

(27316026) I started the study slightly overweight by BMI and mostly interested in helping out along with seeing how it went firsthand. I’m 35 and 5’9 and my weight has been slowly going up on average for a decade, interrupted by harsh diets every few years to try and get back down under 160. I’ve always succeeded at these diets, which normally lasted around 2 months and involved meticulous calorie counting. I hated these diets and was only able to maintain them with the knowledge that they would be over relatively soon. Comparatively the potato diet has been a joy. It only took a few days to settle into, but after working out a few dishes I enjoyed I wasn’t hungry and food cravings were largely absent.

(95730133) I was pleasantly surprised with the amount and consistency of weight loss on this. 2.5 lbs a week is pretty dramatic and this was even easier to stick to than when I’ve done calorie counting previously at a shallower slope (1.25 lbs/week).

(29550957) This is pretty much the best diet I’ve ever been on, including earlier this year when I also ate mostly potatoes- but with tons of dairy (butter, sour cream, cheese) on them. Despite literally messing up an entire week’s worth of days, I seem to be durably down about 10lbs.

(30719090) This has been quite a revelation:

I have been dieting on and off for about 10 years now. The only successful diet was 10 years ago when I got down to 75kg (165lbs). This was based on buying an expensive range of low carb meals. I was less overweight at the time and it was something of a struggle. The diet was eventually derailed by personal circumstances and I have since then gradually increased my weight reaching 200lbs and over recently.

All other diets I have tried have had a small loss initially, but the loss has never continued. The psychological difficulty of maintaining a restricted diet when the losses did not continue was always too much for me. I hate the feeling of being hungry.

The potato diet has been very different. I actually like potatoes so I have not found it difficult to eat them every day and I have found it very easy to resist the temptation of other food.

(35182564) Since I was very successful, losing more than 20 pounds in six weeks, I will probably continue some more relaxed form of the diet for a few more weeks. I have been trying to lose weight for years with absolutely no success. The potato diet did in six weeks, what I could not accomplish in many years. I hope I can keep the lower weight (will send an update in a few months).

(05999987) As a person who has slowly gained weight over the years until I hit the border BMI between overweight and obese and it has become very difficult to lose weight. I’ve often done a couple weeks of limiting to 1500 kCal/day with what a normal person would think healthy–lots of vegetables, some whole grains, some lean proteins, olive oil, legumes. Every time I’d lose a couple pounds, but not much more, and find myself to be quite hungry most of the time. The main difference with potato diet is that I only once experienced the brain-crashing feeling that I need to eat something immediately because my brain is no longer working due to the colloquial usage of “low blood sugar”. The rational part of my brain also didn’t notice any hunger and I could read about/watch people eat/think about delicious foods and not feel like I really wanted to eat them, and I’m the sort of person who thinks about cooking a lot. Plain cold potato was just fine with me, and while I looked forward to the end of the diet and eating normal food again on a theoretical level, I didn’t care about adding condiments, etc. 

(63833277) I occasionally had french fries or tater tots or even a couple of times pringles. My wife used some dairy in preparing the mashed potatoes and had ketchup on my fried potatoes, so probably technically every single day should have a “1” in the “broke diet” field. But if I’d done that I’d never have been able to stick with it as well as I did–I basically tried to bend the diet such that I could successfully stick with it but no further and call that success. I thought about retrospectively changing them all to 1s but there *were* days when I *actually* broke the looser diet I’d set for myself and I didn’t want to elide that distinction. Basically think of my diet as a slightly loose potato diet that’s like 95%-97% potatoes instead of 97%-99% as expected. Sorry for not being ideal about that, I figured that would be better than giving up after 5 days.

DESPITE THE DEVIATIONS, THE DIET WAS AN ASTOUNDING SUCCESS!

I’ve never lost weight before. My life has been a slow drumbeat of “this is my setpoint weight, I can’t lose any but I don’t gain any” punctuated by “Life event, my setpoint weight is now X lbs higher than it used to be”. I was never able to motivate myself to stick with diets because I was constantly half-assing them, thus not losing weight, thus seeing no point in sticking with a diet that wasn’t losing me weight.

I lost half a pound a day on this potato diet. I am astounded, as is everyone who knows me!

The potato diet is not a willpower diet. Some people saw huge effects even while cheating. Some people saw huge effects on this diet even when they had found other diets super hard in the past.

We understand if you don’t really get this. We didn’t get it either, despite reading about all the previous success stories, until one of us tried the potato diet for ourselves. Hunger vanishes in a really weird way that is hard to describe to anyone who hasn’t felt it directly. So listen to all our participants who are like “no it’s not calories, it’s not willpower”. Or try it for yourself, you might be surprised! 

Anyone else who complains about calorie-counting will be thrown directly into the sun.

Carbs make you fat

Some people think that carbs make you fat. But the potato diet seems like bad news for any “carbs make you fat” theory, since potatoes are starchy carbs. More complex versions might still have a leg to stand on, but obviously this finding is a problem for this kind of theory.

Seed Oils

There’s a theory that the obesity epidemic is caused by “seed oils”, an umbrella term for things like canola oil, soybean oil, corn oil, sunflower oil, and peanut oil. We’ve previously reviewed this theory, and found it unconvincing.  

We didn’t track the oil people were eating in any rigorous way, but many people had seed oils like canola and peanut oil on their potatoes. Since their diet was otherwise so limited, this seems like a problem for seed oils theory.

On the other hand, the amount of oil they were eating did seem to make a difference for some people. So maybe this is more evidence for “something that is sometimes in oil and sometimes not”. It fits pretty well with contamination theories (more in a bit), or anything else that might vary in oils, perhaps due to factors like different growing conditions.

Long-Term Theories

There are some theories that suggest that the obesity epidemic is the result of what we’ll call “long-term” factors. For example, evolutionary theories say that natural selection is, for some reason, pushing us towards greater body weights over time. Epigenetic theories suggest that things that happened to your parents or grandparents cause obesity, as the result of gene expression. 

Developmental theories say that people become more obese later in life because of something that happened to them early on in development or childhood. This recent massive review paper specifically argues “that obesity likely has origins in utero,” i.e. you get obese at 25 because of things that happened to you when you were an embryo.

But the potato diet poses a challenge for these theories. If obesity is caused by something that happened to you in utero, or by something that happened to your grandmother, then how come it can be reversed in a couple of weeks of potatoes? There may be ways to resolve this challenge, but it’s a challenge nonetheless. 

Mono Diet

Some people have told us, “oh you can eat any one thing and lose weight like this”. Penn Jillette also says this. He told “Good Morning America” in 2016:

It didn’t have to be potatoes, they aren’t magic. I picked potatoes because it’s the funniest word. I could have chosen beans or just almost anything.

We’re not so sure. In particular, why do people think that other mono diets work? We haven’t seen any. We encourage anyone to find anecdotes, studies, or better yet, run their own Onion Diet study or whatever.

The potato diet isn’t even really a mono diet. We explicitly allow for oil and seasonings, and lots of people lost weight with tons of cheat days. The mono-ness (monotony?) of the potato diet clearly is not the active ingredient. 

Potatoes are also unusual in that they are (almost) nutritionally complete. You couldn’t do the white bread diet and get far. But you could maaaaaaaybe do the whole wheat bread and oil diet, or the wheat bread and cheese diet. Also known as: the basic daily diet in Europe for centuries.

That said, we do think that studies (maybe more internet community trials) of other very simple diets would be interesting — especially since most cultures historically have had very simple diets, which shows there are many simple diets you should be able to live on indefinitely. So we’d love to see, for example, studies on diets composed exclusively of: 

• Rice & beans
• Rice & fish 
• Rice & lentils
• Buckwheat soba & edamame
• Bread & olives / olive oil

(Someone should check that these are nutritionally complete first, though.)

This last one is already close to the Mediterranean diet, but it would be interesting to cut the Mediterranean diet down to literally just bread, olives, olive oil, wine, and cheese. Or literally to just bread and olives / olive oil, if you could survive on that. 

So anyways, if you are sure that any mono diet would work, please do run your own study, we want to see it. We’d be happy to discuss study design with you!

Food Reward

Some people put the obesity epidemic down to a factor called “food reward”. They say that people are obese now because food has gotten more delicious, and that the potato diet causes weight loss because potatoes aren’t delicious. An attempt to describe the theory might look something like this:

People are more obese because food is way more fun to eat now. You can even be agnostic about why food is more fun to eat, and maybe it’s a million small reasons. But over time food producers have figured out how to hit that mental g-spot that makes people go YUM, and when you do that, people eat more than they should and they gain weight. The potato diet works because potatoes are boring and so people don’t overeat.

To be frank, we still don’t really get this theory. That is, we don’t think it makes sense. 

First, we’re not convinced modern food is more delicious than old-timey foods. They had butter and ham and sugar and ice cream and even donuts back in 1900. Check out our review of foods of the 1920s and 1930s — lots of the food culture was weird, but they also had like, just tons of lard and pie. 

Second, if the problem is that Doritos and Kraft Singles have been hyper-engineered by food scientists to be irresistible, then how exactly would the potato diet pry people away from them? If they are irresistible, then it should be really really hard to stop eating doritos and start eating potatoes. But people say that it doesn’t take much or even any willpower to stay on the potato diet, and many people report no cravings. If your model is “people eat the most delicious foods available and cannot help themselves”, then the only way the potato diet could hold people’s attention is if straight potatoes are more delicious and addictive than twinkies. 

Frankly we think they are more delicious than twinkies — but if that’s true and food reward is the law of the brain, then fast-food companies should be peddling baked potatoes instead of Snickers bars. 

Finally, the food reward perspective predicts that the potato diet works because potatoes are boring so you don’t want to eat them. We think this is also bunkum. Potatoes are great, and everyone knows it. Lots of participants reported not only enjoying potatoes, but liking them more after completing four weeks of the study:

(24235303) I didn’t mind eating potatoes.  They were still perfectly tasty throughout, and varying form factor and spices kept things fresh enough.

(02142044) I felt a sort of euphoria/hypomania that lasted from day 17 to day 20, and I’m unsure how to reproduce it … It was both a feeling of well-being, but also the potatoes started feeling delicious, like they were extremely savory.

(29550957) The last two days my family forced me to eat a bunch of other stuff for my birthday and honestly I wasn’t super enthusiastic about it! I wish I could have just been eating more potatoes. I notice I definitely felt worse after eating stuff like cake, and actually felt durably very stuffed for hours afterwards.

(31497197) Overall, I’d say the diet “works” in that I ate as much as I wanted, mostly didn’t crave other food too often, never got sick of potato, and lost weight.  On the very relaxed diet, I lost an average of 2lbs/week, and I think that would have been higher with less frying, but commercial food is not conducive to diets at the best of times. … This is really easy, in that I don’t hate potatoes and haven’t gotten sick of them.

(16832193) I was quite surprised that I didn’t get tired of potatoes. I still love them, maybe even more so than usual?!

Participant 57875769, Day 11: 

My wife and I went out to eat with a friend and I expected to use today as a cheat day, but honestly potatoes sounded like the best thing on the menu so I ordered hash browns and french fries. The hash browns were very filling on their own so I didn’t eat many of the fries.

And again Day 29: 

I’m ending today. It’s weird though, I’m thinking of all the foods I could eat today and I might just stick with potatoes for a lot of my meals. It’s going to feel strange going back to a more varied diet.

So, people come out of the diet saying they love potatoes. Many of them choose to keep eating potatoes even though they’re off the diet. Some of them say they MISS eating so many potatoes. If this isn’t what people mean by “food reward” or “palatability”, then we’re not sure what they mean. If people do mean something else specific, we’d be interested in hearing that.

Same thing for satiety. Yes, potatoes are high satiety, in the sense that you don’t want to eat anything else after you eat potatoes. But why are they high in satiety? Why do they make you not want to eat any more? This is borderline circular reasoning. 

Microbiome

Some people think that the obesity epidemic is caused by some kind of problem with the microbiome, the little beasties that live in your digestive system. 

Microbiome theorists have been in contact with us and have shared how they think potato starch is great for the microbiome, pointing us to studies like this one and popular science posts such as this. 

This is really a proposed mechanism, rather than a theory of the cause(s) of the obesity epidemic. It doesn’t explain why the microbiome gets so messed up in the modern environment, but this also means it is potentially consistent with many different theories. If high levels of sugar, fat, light exposure, iron supplements, PFAS, lithium, processed foods, or whatever mess up the microbiome, and something in potatoes fixes it, the potato diet would work just about like we see here.

This seems reasonably plausible to us. In particular, many participants report digestive or gastrointestinal changes (both good and bad) on the potato diet, which is about what you would expect if the potato diet were seriously changing your microbiome. One possible limitation is that weight loss does seem to be driven by the brain, but there may be a gut-brain connection that renders this point moot.

That said, we’re not sure how to test this hypothesis any further. We could compare the potato diet to a normal diet supplemented with potato starch, but if the potato starch supplement also caused weight loss, that wouldn’t point to the microbiome specifically, it would just show that the potato starch contains the same active ingredient as the potato diet, whatever that is.

We could also test stool samples, but honestly we don’t know what we would be looking for. Yeah some things would probably change in your microbiome after four weeks of potatoes, and we could see if any of them were correlated with weight loss, but that’s a pretty blunt instrument. What should we actually look for? If anyone has opinions on *exactly* what might be going on with the microbiome, we’d be interested in hearing your theory.

Processed Foods 

“Processed food makes us fat” is a line that has been pushed by outlets such as the Washington Post and the NIH. The basic idea is pretty simple: ultra-processed foods make you fat, for some reason. People who support this perspective don’t usually say what it is about these processed foods that make them so fattening, but it’s often mindlessly conflated with the food reward theory:

It also doesn’t mean that all processed food is bad. Whole-grain bread and cereal are excellent, and there are good versions of such things as frozen pizza and jarred pasta sauce. Also wine.

What it does mean is that modern industrial food processing — and only modern industrial food processing — has enabled the manufacture of the cheap, convenient, calorie-dense foods engineered to appeal to us that have become staples of our obesogenic diet.

This perspective does seem to predict that the potato diet should cause weight loss, because potatoes are super unprocessed, about the rawest food most people are likely to eat. Participant 20943794 does a nice job pointing out just how unusual potatoes are in this way:

Potatoes are a lot less processed than most food I eat … even the dishes I “make” “myself” have a big pre-made components. For example, when I “make” spaghetti, I used dried noodles that were made in a factory, a jar of sauce that was made in a factory, and beef that was butchered in ground in (at least) an industrial kitchen, if not another factory. The only stuff that’s really raw is the vegetables I chop and add.

So at first glance, the potato diet looks good for the idea that processed foods make you fat.

But there are some problems. First off, even if processed foods make you gain weight, that doesn’t necessarily mean that unprocessed foods will make you lose weight. Foods high in cyanide will kill you, but foods low in cyanide won’t bring you back to life (as far as we know, maybe someone should check). 

We also want to say, we really think this is a non-theory. Even assuming processed foods do make you fat, this isn’t a theory (in our opinion) because it doesn’t address the question of WHY processed foods make you gain weight. 

For comparison: in this study, we’ve found that eating enough potatoes makes you lose weight. But “the potato theory” isn’t a good explanation for the potato diet; we want to know what about potatoes makes this happen! So we really demand to know what it is about processed food that (potentially) makes people gain weight. Treating “processed foods” as a theory itself is at best circular reasoning (“processed foods make you fat because they are processed foods”). 

Not to say that there aren’t potential versions of this idea that do work as a theory. Processed foods might be uniquely low in nutrients that we need to stay lean (potassium?). Or, since they spend so much time in contact with industrial machinery, they might be especially high in obesogenic contaminants.

Contamination

There are all kinds of contaminants in the environment that didn’t used to be there. We know that some chemicals can cause weight gain in humans and animals. With these two facts in mind, we think it stands to reason that the obesity epidemic could be caused by one or more contaminants that are getting into our brains and messing up our ability to properly regulate our body weight. We presented a version of this theory in our book/series A Chemical Hunger, and while we don’t think it’s a sure thing, we do think that there’s a lot of evidence in favor. 

The potato diet is definitely consistent with the contamination theory. Since potatoes are so incredibly unprocessed, they are presumably unusually low in most contaminants. Whatever contaminant you might be concerned about, there is probably less in a plain baked potato than there is in a steak, candy bar, or box of pasta. 

The main wrinkle here is that weight loss on the potato diet is so fast, which is a little weird if we assume that the obesity epidemic is caused by contaminants. It seems like something about the potatoes would have to either stop the contaminants from messing with your lipostat, or would have to rapidly flush the contaminants from your body. 

Lithium

We think lithium may be one contaminant contributing to the obesity epidemic (we covered this in Part VII and Interludes G, H, and I of A Chemical Hunger, and we published some correspondence with a specialist here).

Briefly, the lithium hypothesis looks plausible because lithium causes weight gain at clinical doses, and we know people are exposed to more lithium now than they were back in the 1960s. The only thing is, how much lithium do you need to get exposed to before you start gaining weight, and are we getting exposed to at least that much? We’re working on answering these questions, but we have found some evidence that people get exposed to quite a bit in their food (though it’s complicated). 

The fact that the potato diet causes weight loss isn’t really strong evidence for or against the lithium hypothesis. But we do want to point out, it’s consistent with the lithium hypothesis.

Potatoes are high in potassium, and there’s evidence that potassium competes with lithium in the brain in interesting ways. If obesity is caused by your brain getting all gummed up with lithium, and potassium makes it stop, then the high levels of potassium in potatoes would be the sort of thing that might cause lots of rapid weight loss.

Participant 02142044 mentioned this hypothesis: 

You probably already know this, but I find it credible a potential reason as to why the diet works, if it does, is that it is helping clear lithium, which would also help explain the mild hypomanias people experience. https://jasn.asnjournals.org/content/10/3/666 seems to indicate that potassium and sodium can help with clearing lithium. That is also why I started salting more.

The fact that the potato diet causes hypomania in some people and fear & grief effects in others is also maybe consistent with lithium, since lithium is both an antimanic and a sedative.

Another mark in favor is that we do have some idea of what foods may be high in lithium, and there are a few hints that these foods can boot people out of potato mode and stop their weight loss. In particular, we have reason to think that tomatoes are often high in lithium, and one of our participants reported this: 

Another food group that we think is often high in lithium is dairy, and there’s again some evidence that eating dairy can limit the potato diet. Consider this story from participant 29550957:

This is pretty much the best diet I’ve ever been on, including earlier this year when I also ate mostly potatoes- but with tons of dairy (butter, sour cream, cheese) on them. Despite literally messing up an entire week’s worth of days, I seem to be durably down about 10lbs.

If this is the case, then cheating on foods that are low in lithium should always be fine, and may explain why people were able to cheat on this diet so much and still see the effects.

Cheating on foods that CAN be high in lithium is a gamble. A crop that concentrates lithium won’t grab much if it’s grown in a lithium-poor environment, but will be totally loaded if it’s grown in a lithium-rich environment. So it’s quite possible that that e.g. some ketchup is loaded with lithium and some isn’t, depending on where it was grown, how it was processed, etc. This would look like ketchup making a huge difference for some people and not at all for others.

Unfortunately we still don’t have a great list of which foods are high and which are low in lithium. The list we do have, we don’t particularly trust, which is why we are gonna do our own survey of the food supply.

However if we had to guess right now, our best bets for foods that are high in lithium (and if this hypothesis is correct, might inhibit the potato diet) are: Eggs, milk, soft cheeses (but maybe not butter or hard cheese?), anything containing whey, tomatoes, goji berries, leafy greens, beef, pork, carrots, and beets. But again, this list ain’t gospel. 

One point against the lithium-potassium hypothesis is that participant 23300304 sent us blood work from both before and after the diet, and his potassium levels only went from 4.0 mmol/L to 4.5 mmol/L, both within the normal range. But blood levels may not be relevant, since this kind of thing tends to be under tight biological control, and of course we know that potatoes are high in potassium.

If the lithium-potassium competition hypothesis is true, other high-potassium, low-lithium diets might also cause weight loss. There’s a little bit of evidence that potassium consumption is related to successful weight loss, which makes this seem plausible. 

But straight potassium supplementation may or may not work. At first we thought you could just give people potassium salt and see what happened, but we talked to a specialist who studies lithium clearance from the brain, and he said that the bioavailability of potassium from different sources complicates this a lot. We’re still trying to figure out what a good design for this study would be, but it’s not necessarily as simple as “consume a lot of potassium, avoid tomatoes and whey, and lose a lot of weight”, though we suppose someone could try it and see. 

Looking at lithium and potassium in the urine of someone doing the potato diet might help with this, and so we’re considering asking for urine samples in future studies. But it might also be inconclusive.

For example, maybe lithium raises your lipostat set point by gumming up the brain somehow, and high levels of potassium lower the set point by increasing lithium clearance and forcing it all out of the brain. Lithium that gets forced out of the brain has to go somewhere, and if this were the case, it would probably end up in the urine, so you would see elevated levels of lithium in people who enter potato mode.

But maybe lithium causes obesity by forcing potassium out of the brain, and high levels of potassium cure obesity by supplementing potassium faster than the lithium can clear it. If something like this were the case, you might not see more lithium in people’s urine when they go on the potato diet. 

Probably neither of these explanations are exactly correct — these are just examples to show that urine tests during the potato diet might be a good idea, but won’t be conclusive. 

Something else about Potassium

But it’s also not like potassium and lithium are married. Potassium could still cause weight loss even if the lithium hypothesis is totally wrong. Potatoes are notorious for being high in potassium, so it’s reasonable to suspect that this might be the active ingredient.

That said, if it’s not lithium, why would potassium cause weight loss? We don’t know. Any ideas? 

Don’t most theories predict weight loss on the potato diet?

Well, yes and no. Many theories do predict weight loss on the potato diet; but most theories don’t predict potato mode, this state where hunger disappears and you (occasionally) feel charged with incredible energy.

Finally, to anyone who thinks they knew it would work in advance… 

Ok wise guy. 

If you predicted (or could have predicted) that the potato diet would cause this kind of weight loss, or if medical / nutritional science could have predicted that this diet was going to be so effective in the short term, and so easy for so many people — then why haven’t doctors and nutritionists been recommending the potato diet to people alongside diet and exercise?

Why did all these popular press articles have doctors and nutritionists throwing a fit about how dangerous and unhealthy the potato diet would be? Look at these comments they got on stories about Andrew Taylor, who lost over 100 lbs on the potato diet:

“I personally would not recommend it,” says Dr. Nadolsky. “It’s very restrictive. A vegan diet is very restrictive and a ketogenic diet is very restrictive, but a potato diet is one of the most restrictive diets you could ever do.” … the diet itself would be very hard to stick with for most people, says Dr. Nadolsky.

Or this, from a story about Penn Jillette: 

This type of extreme diet can pose serious health risks due to its severe limitations. “While there’s no doubt that potatoes — just like all vegetables — are supremely nutritious, eliminating almost all other food groups in totality is not only dangerous, but can really backfire,” says Jaclyn London, M.S., R.D., Nutrition Director at the Good Housekeeping Institute.

If you knew the potato diet would work, why did you not run this study many years ago? Why are there no clinical trials? Did you think people would not be excited to see this result? 

Guess the NIH is too scared of the tater.

8. How to Potato Diet if you want to Potato Diet

We’re not currently accepting signups, but we know that some of you will want to try the potato diet for yourselves. So here is some current advice, from us and from some participants.

First, our advice:

• When you start off, try eating mostly (> 95% of your calories) potatoes, with a little oil, and as much hot sauce and salt as you want. You can also have zero-calorie beverages like black coffee and tea. This seems really strict but many people find it to be much easier than they expected, so give this version a try first. 
• If you feel bad/weird and are like “I can no longer stand potatoes!”, try:
  • Eating a potato. Hunger feels different on this diet and you may not realize that you are hungry. Yes, really. 
  • Drinking water. It’s really easy to get dehydrated on this diet, and again you can’t always tell. 
  • Eating a different kind of potato. There are many varieties, try mixing it up. You will almost certainly want to eat more than one kind of potato.
  • Peeling your potatoes. Eating less peel / no peel seems to help some people with digestive and energy issues, especially after a few days on the diet. 
  • Eating more salt. Potatoes are naturally low in sodium and you may not be getting enough. 
  • Getting sunlight. Potatoes have no vitamin D, you may be craving that.
  • If none of these other things help, do a cheat meal and eat whatever you’re craving. (But maybe still avoid dairy?) If you find you keep taking cheat meals, go ahead and drop down to the 80%, 60%, or even a lower % potato diet. The 40% potato diet works just fine for some people. 
• If you still feel bad after trying these steps, stop the diet. If you are suffering then the diet isn’t working anyways, and you shouldn’t take risks with your health. Plus life is too short to do things that make you miserable.
• If the diet is easy but you’re not losing weight (or otherwise not seeing effects), try doing 100% potato, no oil.

And here’s some advice from participants:

(33217580) I found that despite all the warnings, it was really easy to underprepare and end up with not enough food. The days where I either had done enough prep or just had time to go cook were definitely much simpler than the days where I would have been happy to just eat some boiled potatoes, but sadly the tupperware was empty, and I got really hungry, ate chips or fries, was a little lower on energy or moodier etc. If I’m going to continue (and I might, because it worked so well!), I’m going to aim for comically large  proportions in food prep, because then I might actually have something close to enough.

(31664368) Advice: figure out a way to exit the diet gracefully. I have a robust belly, but significant GI issues I am still going through. Perhaps it was 1 thing I ate that set things on a bad track for several days. Trying oatmeal and crackers as easy non-potato food, but would love a playbook of how to get back to feeling solid after eating a burrito.

(14122662) If I were doing this again, I might also invest in a nice knife. I noticed that chopping the potatoes each day was effortful and a strain on my hand. Being able to slice through the potatoes more cleanly would have been a nice convenience.

(63187175) It requires a lot of preparation and staying ahead of your meals. Potatoes aren’t something you can just grab out of the cupboard and eat, there’s always some amount of cooking required and (at least in my limited experience) that cooking is either quite labor or time intensive (and usually both). If I do this again, my main takeaway lesson is that to be successful in sticking to it, I need to very deliberately over-prepare and always make way more than I want at a time. Just-in-time preparation is way too hard to follow. When I get home from a long day at work and discover that there are no potatoes already made, those were always the moments when I absolutely hated this diet. Even worse, I ran out of potatoes many times during these 3 weeks and had to take a trip to the store before I could even start cooking. Another area where I’d be more diligent if I try this again.

(02142044) How I’d do it again

– Ensure that my weighing scale is reliable

– Keep not using oil

– Stick to the diet strictly throughout

– Only eat potatoes boiled in their own water (mostly or only yellow?).

– Buy them in bio market if possible?

– Probably still eat sweet potatoes weekly for vit A?

– No exercises during this period.

– Do it in a period with less changes in my life overall (no medication, no changing location in between, no big relationship changes, etc)

– Keep filtering water throughout

– Change the way I track thing:

  * Note how much kg of potatoes I eat each meals.

  * Change “Mood” to “Lowest low”, “Highest high”, “Irritability”, “Fluctuation” and “Highest calm/plenitude”

  * Keep track of “How tired am I of this diet?”

  * Also note what is happening in my life to see other kinds of corelations.

– Supplement in B12 way more, salt my meals from the beginning

– No garlic. Cayenne pepper and tabasco are okay

(81125989) Advice to others trying the diet:

Feeling lazy? Trader Joe’s olive-oil Kettle-cooked potato chips for the win. Only three ingredients – potato, olive oil, and salt.

Choose cooking methods that are very low-prep-time, yet high-bulk. At first, I sliced potatoes before baking – this took over an hour each time and only made enough for one meal. Eventually, I realized I could just cut slits in whole potatoes, coat ’em in olive oil & salt, and dump ’em in the oven. Easy & makes enough for 2 days.

Variety is the spice of potato life. Get different kinds of potato, or you will get so intensely bored. (Also, get sweet potatoes for Vitamin A. Maybe placebo, but I noticed my evening low-light vision got worse, but improves the day after I eat sweet potato)

Schedule cheat days? I’ll have to wait to see your full analysis on the dose-response of the potato diet (weight loss vs days cheated)… but if the dose-response is good, then I recommend scheduling cheat days to stave off boredom. (Also, for social eating.) In particular, I ate red meats to get my B12. You can also eat liver or clams. Also potato has no Vitamin D, go get lots of sun or eat dairy/fatty fishes. (I don’t trust supplements; every time I’ve looked at a pre-registered RCT of a vitamin supplement, it’s either near-zero or somehow way less than just eating a whole food that’s known to be a source of it.)

(31497197) Howtos:

 – Buy lots of potatoes.  Bake off or boil off five or ten pounds every couple days, then refrigerate to eat, mash, fry as wedges, roast as cakes, etc.  

 – Takiea baked potato that can be microwaved as needed, and or a small tupperware thing of mashed potato with some chilli/garlic/hot sauce in it when going places for long enough that being hungry will come up, but tables/utensils/microwaves etc will be available.

 – Properly flavored mashed can be used as a dip for potato chips or something when going camping, etc.

 – If with a group at a restaurant, order fries, or just have a beer.  The mashed potato might be full of dairy fat.

 – When eating non-potato snacks, make a note and carry on.  Make sure they aren’t dairy.  

 – Make peace with breaking the diet for a meal every so often.  It will happen sooner or later.  Try not to, but eventually (group camping, or a nice restaurant, or something) it will be better to break the diet than not.  Do so, and get back on potato immediately afterwards.

(21112694) While I only did about five whole days of the diet, I would highly recommend a 1-2 day transition off the diet. The day I ended, I went out for an event and had a large dinner which my digestive tract was not ready for. I typically have no issues with my GI tract, so I figured it wouldn’t be an issue given the shorter diet period. It could have just been a one-off random occurrence, but if you see this trend pop up more, it may be beneficial to suggest a slower transition off the diet, especially for those with GI issues like IBS (I don’t have any). 

9. What’s Next

We’re very happy with this study, but there are some major limitations. Almost all of our participants were white, and most of them were Americans. We expect these results will generalize to other groups in other contexts, but frankly it’s not in the data. 

The potato diet definitely causes weight loss, but a few major questions remain. Questions like, why do some people hit a wall immediately, and find the diet impossible after only a few days? Why do a few people suddenly hit a wall after about 3 weeks?

What’s up with cheat days? Does the 80% potato diet work for everyone? Can some people lose weight on the 40% potato diet? What about the 20% potato diet? The SMTM author who tried the potato diet didn’t lose any weight until they cut out all oil, at which point they started losing about a pound a day. So for some people it seems like the 100% potato diet is really necessary? Is that true? Why would that be? 

Is the attrition rate really higher, and is the diet more difficult, for women / people with two X chromosomes? If so, why? What about trans people? If there’s a chromosomal effect, how does it interact with exogenous hormones?

All of these are questions that would be good to answer in future work.

Our current plan is to follow up with our participants in 6 months, 1 year, and 2 years (assuming it’s still interesting/relevant at that point). We’ll make posts with those results, and share the data publicly, as these followups happen, so look for the first followup post about six months from now.

We may also go back into these data and do more analyses, since there are almost certainly more things to find in the data we’ve already collected. 

Also, expect a forthcoming post on reflections about doing this kind of shoestring internet science. Keep your eyes peeled.

We’re not currently taking signups, but if you want to try the potato diet for yourself, why not track your data using a structured spreadsheet, so all resulting data will be standardized. You’re welcome to download a copy of THIS FORM and follow the instructions, and you can send us an email with your copy of the form when you’re done. Just include the words “Potato Diet” in the email title so the emails are easy to sort and track.

If we can secure funding, our next study may be “potato camp”, a project where we send 20 or more overweight & obese volunteers to a summer camp and serve them nothing but potatoes for four weeks. This would allow us to replicate these results in a slightly more controlled fashion, collect things like urine and serum samples, and so on. And it would be a pretty good deal for participants — we’d make sure there’s wifi, so if you have a remote job, you can just drop by for four weeks and keep working as normal. If you’d be interested in attending potato camp, SIGN UP HERE. If you’d be interested in funding this project, contact us. 

We might also run other studies, but we’re still figuring out what would be the best and most fun use of our time. Maybe we will run something on potassium. Or maybe our next study will be unrelated to obesity, it’s not the only interesting research topic in the world.

If you would like to be notified of future stupid studies like this one, SIGN UP HERE. You can also just subscribe to the blog itself by email (below), or follow us on twitter, if you want to keep up with our work in general.

And if you feel like reading this post has added a couple of dollars’ worth of value to your life, or if you have lost weight on the potato diet and you think it improves the quality of your life by more than one dollar a month, consider donating $1 a month on Patreon. 

Thanks for going on this journey with us.

Sincerely, 
Your friendly neighborhood mad scientists,
SLIME MOLD TIME MOLD

[PEER REVIEWED BY ADAM MASTROIANNI]

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End Note: Academics, you may cite this report as–

Time Mold, S. M. (2022). LOSE 10.6 POUNDS in FOUR WEEKS with this ONE WEIRD TRICK Discovered by Local Slime Hive Mind! Doctors GRUDGINGLY RESPECT Them, Hope to Become Friends. SLIME MOLD TIME MOLD.