A Chemical Hunger – Interlude A: CICO Killer, Qu’est-Ce Que C’est?


Runner up titles: Son of CICO, 2 CI 2 CO, Revenge of CICO, CICO 2: Judgement Day, CICO Returns, CICO! Here We Go Again, CICO’s Bogus Journey 

Calories In Calories Out (CICO) gave us more trouble than any other section we worked on when writing A Chemical Hunger

Part of the problem is that CICO means different things to different people, and covers a number of loosely related hypotheses. We found it hard to disentangle these when we were writing Part II. A number of times we circled back to our section on CICO and tried to reorganize it, or re-write it entirely, but we weren’t able to figure out a way to clarify the argument to our satisfaction. 

But feedback on the posts has proved extremely helpful, and we think we can now do a better job explaining what we meant. Special thanks to commenters-on-the-blog Richard Meadows and Grat Ivar, to fellow bloggers Alvaro de Menard and Stephen Malina, and commenters on MetaFilter and Hacker News, for helping us clarify our thoughts on this.

Linear Relationships

One way to interpret CICO (or one sub-hypothesis) is that it claims there is a strictly linear relationship between calories eaten/burned and weight change. This is specified if we take “weight gain = calories in – calories out” literally. Essentially, this hypothesis says that overeating by the same amount should always lead to the same amount of weight gain.

This is clearly false. The overfeeding studies provide extremely strong evidence against this version of CICO, since people gain very different amounts when overfed by the same amount, the difference appears to be mostly genetic, and some people actually lose weight, even when overfed by moderate (1000 kcal/day) amounts. Many people still believe something like “for every extra 3500 calories you eat you always gain one pound”, but all available evidence comes down very strongly against that.

At low levels of overfeeding, people at normal weight often don’t gain any weight at all. We liked how sdenton4 on Hacker News put it: “It’s pretty obvious the body has other ways to dump excess calories than turning them into fat stores.” 


In Part II, we quote Stephan Guyenet as saying, “This model [CICO] seems to exist mostly to make lean people feel smug, since it attributes their leanness entirely to wise voluntary decisions and a strong character. I think at this point, few people in the research world believe the CICO model.”

What does Guyenet mean here? A common interpretation tied up in CICO is that differences in willpower explain the difference between obese and lean people. The idea is that weight gain is easy and weight loss is hard for everyone. This interpretation says something like, everyone would be 300lbs if they didn’t use their willpower to eat healthy foods rather than cake — you have to control yourself. From this perspective, people who are obese lack willpower and people who are thin/fit are virtuous resisters of temptation.

The overfeeding studies also provide strong evidence against this hypothesis, since they find that it is hard for most people to gain weight and easy for them to go back exactly to the weight they were before the overfeeding. We think this leaves “willpower” explanations dead in the water. Most skinny people have no trouble staying that way.

While not everyone means this when they say “CICO”, many people do, and we wanted to address this aspect of CICO because it is a common misconception. There’s also a strong moral reason to argue against this aspect of the hypothesis, because the idea that obesity is the result of lapses or weakness in willpower has been used to justify many cruel and ineffective positions. People who believe that obesity is the result of laziness and weak willpower believe that people with no moral fiber can be recognized on sight. As a result, they do things like treat overweight and obese people with disrespect, make jokes about them, don’t hire them, don’t give them proper medical treatment, etc. They think that shaming and social stigma are effective interventions against obesity. Some think that overweight and obese people should feel ashamed of their weight. This is as horrible as thinking that cancer patients should feel ashamed and responsible for falling sick. 

In addition, placing the blame on willpower and moral failing, and treating individual responsibility as the appropriate intervention, means abandoning the search for the causes of obesity. If you think obesity is largely the result of willpower, then there’s no mystery or need for a solution. But in fact obesity is not the result of willpower, and obesity remains very mysterious. Let’s quote that article from The Lancet again: “unlike other major causes of preventable death and disability, such as tobacco use, injuries, and infectious diseases, there are no exemplar populations in which the obesity epidemic has been reversed by public health measures.”

Calories Lead to Weight Gain

Another interpretation is something like “calories matter for weight gain”. Other things being equal, you generally gain weight when you eat more calories and you generally lose weight when you eat fewer calories.

We are not trying to argue against this at all! If you eat 400 kcal/day, you will lose weight (there are studies on this). If you eat 10,000 kcal/day, you will gain weight (there are studies on this one too). But the amount of calories you eat matters much less than most people think, and there isn’t a strong linear relationship between calories consumed and weight gained (see above).

You can lose weight by consistently eating at a calorie deficit, but people who do this either struggle to maintain their lower weight or gain it back. For two people who are the same height, one might weigh 150 lbs and the other weigh 200 lbs. If the 200 lb person loses 50 lbs, it will be hard for them to maintain a weight of 150 lbs, but easy for the person who weighed 150 lbs to begin with. Why is that? And why has the number of people struggling with their weight grown so dramatically since 1980?

There may be some people with exceptional willpower and incredible support systems that can lose lots of weight and keep it off — in the same way that stage magicians with incredible willpower and lots of training can learn to hold their breath for 10+ minutes underwater. The question is why they would need to use their incredible willpower in the first place! Maybe willpower can be a solution, but it’s not the cause — it doesn’t explain the differences between 1980 and today.

What about those Calorie Intake Numbers?

A bunch of readers zeroed in on this paragraph:

It’s true that people eat more calories today than they did in the 1960s and 70s, but the difference is quite small. Sources have a surprisingly hard time agreeing on just how much more we eat than our grandparents did, but all of them agree that it’s not much. Pew says calorie intake in the US increased from 2,025 calories per day in 1970 to about 2,481 calories per day in 2010. The USDA Economic Research Service estimates that calorie intake in the US increased from 2,016 calories per day in 1970 to about 2,390 calories per day in 2014. Neither of these are jaw-dropping increases.

People pointed out that this is about a 20% increase in calories, which doesn’t seem to match our description of the increase as “quite small”. So let’s take a second to unpack our reasoning.

First of all, this was a smaller increase than we expected. We know that even a small daily change adds up over time, but we expected the change in daily calorie intake since 1980 to be much larger. 

Partly this is because once you gain weight, you burn more calories (because it takes more energy to move and maintain physiological function) and you need to eat more calories to maintain your weight. Studies show that people with obesity eat and expend more calories than lean people. From this study, for example, consider this sentence: “TDEE was 2404±95 kcal per day in lean and 3244±48 kcal per day in Class III obese individuals.” From this perspective, the average daily consumption per Pew being 2,481 calories per day doesn’t seem like much — that’s about what lean people expend daily. Obese individuals generally burn 3000+ kcal/day, and while not every modern person is obese, it does make the increase from 2,025 calories per day in 1970 to about 2,481 calories per day in 2010 look relatively small.

This is something of a chicken and the egg problem. We could weigh more because we eat more calories, but we could also eat more calories because we weigh more, and we need to eat more calories to continue functioning at that weight. You may say, “but if you eat less at a higher weight you will dip into fat stores to make up the difference”. Not if your set point is too high you won’t! If you eat less than you need and your body wants to defend your current weight, you will crave food and feel tired and stupid. Sound familiar?

In addition, there’s some evidence that back around 1900 people ate more than they did in 1960, without much more exercise, and they weren’t obese — though take this one with a grain of salt, since for the obvious reasons, we don’t have great calorie data from back then. This is mentioned in the paragraph immediately following the one quoted above:

If we go back further, the story actually becomes even more interesting. Based on estimates from nutrient availability data, Americans actually ate more calories in 1909 than they did in 1960.

For the sake of argument, let’s accept that an increase of 400 kcal/day is a meaningful amount. Let’s further assume that the 400 kcal/day increase is entirely responsible for the increase in the rate of obesity since 1980. Even if the increase is meaningful and driving the obesity epidemic, we have to ask, why are people eating more now than they used to?

Just because calories are causally involved doesn’t mean they’re the “first cause”, the cause we should be looking for. Imagine there were an evil dictator that went around force-feeding people. These people would gain weight (per the overfeeding studies) and in some sense the calories would cause the weight gain. But if we’re being reasonable, the insane dictator is the cause, and the calories are just the mediator. 

We know people do eat a bit more today than in the 1970s. So the question is something like, in this case, what is the insane dictator? When we say “not CICO” part of what we mean is “not willpower”. 


Another point worth mentioning is that there seem to be different kinds of weight change.

One is the kind of weight change that happens around your set point. For most people, changing your weight by 5-10 pounds in either direction will be relatively easy. This may be possible through diet and exercise; the amount of weight change may even have a close linear relationship with the amount of calories you add or remove from your diet! In this limited sense, CICO may be a useful guideline. 

This is very different from major changes in fat mass! All available evidence suggests that it is very, very hard to lose more than 10 or so pounds and keep it off, probably because it involves fighting your lipostat’s setpoint. 

Another kind of weight change has to do with changes in muscle mass. Altering your body composition to have lower fat/higher muscle percentages can occur without changing your set point and result in significant visual differences. We suspect that weight gain and weight loss work differently in bodybuilding because that involves weight change driven by increases in muscle mass, not fat mass. We’re perfectly willing to believe that people can gain and lose muscle mass in a reliable way based in part on caloric consumption, but that’s not the focus of A Chemical Hunger

Cutting fat gained when increasing muscle mass might also be relatively easy, because that’s more fat than you “naturally” had before the gains. More body fat should lead to more leptin, but your body had you at the leptin level it wanted you at before, so the leptin-based part of the lipostat will help you lose that fat mass. But changing fat mass alone seems pretty dang hard.