Only one theory can account for all of the available evidence: the obesity epidemic is caused by one or more environmental contaminants, compounds in our water, food, air, at our jobs and in our homes, that change how our bodies regulate weight.
These contaminants are the only cause of the obesity epidemic, and the worldwide increase in obesity rates since 1980 is entirely attributable to their effects. For any two people in a group, the difference between their weights is largely genetic, because everyone is exposed to similar levels of contamination. But the difference between the average weight in 1980 and the average weight today is the result of environmental contaminants.
3.1 Weight Gain in Response to Medication
We know that this is biologically plausible because there are many compounds that reliably cause people to gain weight, sometimes a lot of weight.
Weight gain is a common side effect of the psychiatric drug Clozapine (Clozaril). On average, people taking Clozaril gain about 10 to 15 pounds. This is dose-dependent — If you take a larger dose, you gain more weight — and on high doses people sometimes gain fifty or even a hundred pounds.
Weight gain is a common side effect of the psychiatric drug Olanzapine (Zyprexa). According to some sources, more than 50% of people taking this drug gain weight as a side effect. In certain populations, the rate of extreme weight gain can be as high as 90%! In one study, a group of 442 people taking Olanzapine gained an average of 30 lbs (13.7kg) after 48 weeks on a normal dose. Other studies find similar numbers — about 20 lbs after a couple weeks and about 30 lbs after a year. There’s some evidence that the weight gain is dose-dependent.
Weight gain is a common side effect of the psychiatric drug Haloperidol (Haldol). In one study, average weight gain on Haloperidol was 8.4 lbs (3.8 kg) at 3 months and 21.3 lbs (9.7 kg) at 1 year. There was a lot of variation between individuals though. If we assume that weight gain was approximately normally distributed, some back-of-the-envelope statistics suggest that about 2% of patients would gain 60 lbs or more after 1 year.
Weight gain is a common side effect of the psychiatric drug Risperidone (Risperidal). In the same study as above, average weight gain on Risperidone was 13 lbs (5.9 kg) at 3 months and 19.6 lbs (8.9 kg) at 1 year. Again there was a lot of variation, and while it’s hard to tell without the raw data, again a reasonable guess would be that some people gain as much as 60lbs. This also appears to be dose-dependent.
Weight gain is a common side effect of the element lithium (lithium), which is often used as a psychiatric medication. Almost all patients seem to gain some weight on lithium, and about half of them report serious weight gain, on average 22 lbs (10 kg). Weight gained is correlated (r = .44, p < .001) with the dosage. Some reports suggest that 20% of patients gain more than 10 kg on lithium.
Unsurprisingly from the lipostat perspective, you’ll notice that all of these are psychiatric medications. Presumably, they affect the brain. Weight gain is a side effect of many drugs, but it’s especially famous in the antipsychotics. Further, weight gain in many of these drugs is associated with enhanced leptin levels.
We need a theory that can account for all of the mysteries we reviewed earlier. Another way to put this is to say that, based on the evidence, we’re looking for a factor that:
- Changed over the last hundred years
- With a major shift around 1980
- And whatever it is, there is more of it every year
- It doesn’t affect people living nonindustrialized lives, regardless of diet
- But it does affect lab animals, wild animals, and animals living in zoos
- It has something to do with palatable human snackfoods, unrelated to nutritional value
- It differs in its intensity by altitude for some reason
- And it appears to have nothing to do with our diets
Environmental contamination by artificial, human-synthesized compounds fits this picture very well, and no other account does.
Mystery 1: The Obesity Epidemic
People were skinny before the modern era because these contaminants didn’t exist back then.
People’s diets were “worse” in the past — full of lard and bread — because diet doesn’t cause obesity. The ~1% of people who were obese in the past were people with one of the various medical conditions known to cause obesity, such as Prader-Willi Syndrome, hypothyroidism, or hypothalamic lesions.
Mystery 2: An Abrupt Shift
People rapidly started getting more and more obese starting around 1980 because the contaminants are the product or byproduct of some industrial process. We’re looking for compounds that were invented around 1960 or 1970, because it would probably take a few years for enough to get into the environment to start affecting us.
Alternatively, these might be compounds that had been invented much earlier, but only began to see widespread deployment around 1980. Either way, we’re looking for that abrupt shift.
Mystery 3: The Ongoing Crisis
The obesity epidemic keeps getting worse because these contaminants continue to be produced and continue to build up in the environment. Every year they accumulate and each of us gets a larger dose. This suggests that we are looking for compounds that don’t break down easily, or at least are being introduced into the environment faster than they break down.
Mystery 4: Hunter-Gatherers
Different groups of hunter-gatherers remain lean while eating very different diets because the human body can thrive on many kinds of food. Some of the diets are extremely high-fat. Some of them are extremely high-starch. Some of them are extremely high-sugar. Some eat an extremely varied diet, while others get almost half of their calories from a single food source. But they don’t become obese, because they’re eating fat right off the gemsbok or yams straight out of the ground, and living in grass huts.
When hunter-gatherers adopt an industrialized lifestyle, however, they become obese just like anyone else. You’ll recall that, in 1990, a team led by Staffan Lindeberg traveled to the island of Kitava and found that none of the Kitavans were obese, despite the fact that they had plenty of foods and ate a very starchy diet.
It’s true that none of the Kitavans living on the island were at all overweight. But there were actually two overweight Kitavans — both men who had grown up in Kitava, had since moved away for many years, and who happened to be visiting at the time of the study. Lindeberg managed to examine one of them, a 44-year-old businessman named Yutala, who had left the island fifteen years earlier to become a businessman in Papua New Guinea. At the time of the study, Yutala was almost fifty pounds heavier than the average Kitavan man of his height, twelve pounds heavier than the next heaviest man, and had the highest blood pressure of any Kitavan Lindeberg examined.
When he moved away from the island, Yutala was exposed to a modern way of living. More importantly, he was exposed to the contaminants of an industrialized society. As a result, he became overweight.
Yutala isn’t an isolated case. In fact, this happens with some regularity. Lindeberg notes, “an epidemic of obesity and weight gain has occurred in former traditional populations that transitioned to a Western lifestyle,” and cites a total of 17 sources to support this claim, including examples from Sudanese communities, Native Americans, Pacific Islanders, South Australian Aborigines, and the people of Vanuatu. “When humans switch from an ancient to a Western lifestyle,” he says, “they experience increased waistlines, reduced insulin sensitivity, higher blood pressure and a host of related disorders and diseases.“
Mystery 5: Lab Animals and Wild Animals
Lab animals and wild animals are becoming more obese because they are exposed to the same environmental contaminants that we are. If they are living around humans, in or around our buildings, eating industrially-prepared foods, or the scraps of such foods, they are exposed to contaminants in the same way as the rest of us. Even if they’re not living in close proximity to humans, these compounds are probably in groundwater and drinking water.
Mystery 6: Palatable Human Food
Lab rats gain more weight from human foods than they do from rat chow with similar nutritional properties because obesity doesn’t come from fat or carbohydrate content, but from contaminants in the food, and human food has more contaminants than the rat chow does, likely from packaging and processing.
Processed foods end up with more contaminants in them — for example, there are 4x more phthalates in Kraft mac and cheese powders than in block cheese, string cheese, and cottage cheese. Another example are these results from the FDA, as reported by the AP. In terms of explaining why the cafeteria diet is so fattening, it’s especially illustrative that grocery store chocolate cake was an extreme outlier, with concentrations of PFPeA more than 100 times higher than chocolate milk.
Doesn’t this mean that avoiding packaged and processed food should reverse obesity? We think the answer is “maybe”. There’s not a lot of research on “whole foods” diets, but the evidence that we do have is quite promising. People seem to lose a reasonable amount of weight and keep it off for up to 12 months when they’re eating largely unprocessed plant-based foods. But we should be skeptical of these results until there are more studies. While this diet lowered almost everyone’s BMI, when we look at individual results, most people remained obese or overweight after 12 months on this diet. Similar findings are characteristic of Paleolithic diets. Even when the studies are conducted by advocates of these diets, they produce very moderate benefits, in one case causing only 6.6 lbs (3 kg) more weight loss than a comparison diet across a 3-month period.
There do happen to be a couple compelling anecdotes. In 2010, Chris Voigt, the Executive Director of the Washington State Potatoes Commission, vowed to eat nothing but 20 plain potatoes (and a small amount of cooking oil) for 60 days straight to demonstrate that potatoes are perfectly healthy, and in fact nutritious enough to sustain a person for quite a while.
This wasn’t intended as a weight loss diet — in fact, 20 potatoes a day was the amount he calculated he would need to maintain his weight (2,200 calories). Despite this, Voigt lost 21 pounds over his sixty-day diet. He even had trouble eating enough — he just wasn’t very hungry. Why would this happen? Well, unprocessed potatoes are about as raw a food as you can find, and won’t pick up contaminants from industrial cooking and packaging. If Voigt was being exposed to contaminants through his everyday diet, then switching to potatoes largely cooked at home would lead him to getting a much lower dose of contaminants.
Most people are likely exposed to some of these contaminants in their diet, so eating a diet with fewer contaminants helps. But most people are also likely exposed at home, at work, and through their drinking water, so diet alone can only help so much.
Mystery 7: Altitude
Obesity is less common at high altitudes because of the watershed. Environmental contaminants build up as water flows downhill and are in much higher concentrations as you approach sea level.
For example, take a look at this map of by-state obesity levels from the CDC:
The Mississippi watershed is America’s largest drainage basin, covering 41% of the country. If you compare this map of state-level obesity to a map of the Mississippi watershed (below), you’ll see that every single state with obesity rates of >35% borders on a river from this watershed system. Also informative is that the three states at the mouth of the river, Mississippi, Arkansas, and Louisiana, are #1, #3, and #4 in the nation in terms of obesity rate (39.5%, 37.1%, and 36.8%, respectively).
Obesity rates are high everywhere in America, but we can see that they are higher in states where the groundwater has covered more distance, and had more time to accumulate contaminants (see continental watershed map below). States where groundwater comes from shorter river systems have a clear tendency towards lower (though still in the range of 25%-30%) rates of obesity.
If this is the case, we should also see similar patterns in other countries.
It’s hard to find good province-level maps of obesity for China, but most of them look something like this:
China has two major rivers, the Yangzi and the Yellow river. Comparing our map of obesity to a map of China’s rivers, we see that Shandong Province, with the highest rate of obesity, is at the mouth of the Yellow River. Shanghai, at the mouth of the Yangzi, is not quite as obese, but still more obese than the neighboring provinces. And in general we see that provinces at lower elevations are more obese.
There are always a few confusing outliers, of course. Why are Maine, North Dakota, and Alabama so obese? In China, why are Xinjiang and Heilongjian provinces so obese? The answer is that watersheds play a role in the distribution of contaminants, but are not the whole story.
In some cases, though, the answer may come back to watersheds after all. For example, Xinjiang province’s main watershed is the Tarim Basin, an endorheic basin that captures water and has no outlet. Rain that falls in the Tarim Basin flows to Lop Nur and stays there. The water might evaporate, but any contaminants it carried will stay in the basin.
We see similar trends in data from Iran. In the map of Iran shown below, you can see that many of the most obese provinces are near the Caspian Sea, another endorheic basin. We weren’t able to find similar maps for Russia or for Kazakhstan, two other large countries bordering on the Caspian, but we would expect them to look similar.
There are obvious and often extreme differences in obesity between people at 0 ft of altitude and 500 ft of altitude, both in the US and in other countries. The changes in CO2 aren’t enough to make any difference, but water runoff could.
It’s important to note that altitude itself doesn’t affect obesity directly. Instead, altitude is a proxy for how high an area is in the watershed, which is itself a proxy for how badly the local water supply is contaminated. This is why Mississippi is more obese than low-lying areas of California. In California the water supply hasn’t traveled nearly as far in its path to the ocean, and has traveled past fewer farms, highways, cities, and factories.
Mystery 8: Diets Don’t Work
Finally, no diet will reliably help because obesity isn’t caused by a bad diet and can’t be cured by a good one. Hypothetically speaking, if there was a person who was only exposed to these contaminants in their food, cutting out the contaminated food for long enough would theoretically cure them. This may be what happened with Chris Voight when he cut out everything but potatoes.
Ultimately, the fact that diets don’t work very well for most people suggests that we pick up these contaminants from other sources than just our food. Probably they are also, to varying degrees, in our water, our workplaces, and our homes.
We aren’t the first researchers who are concerned about environmental contaminants and the role they might play in rising obesity rates. But the scope of this inquiry has traditionally been limited to how contaminants might contribute to the obesity epidemic.
One review focuses on food additives, both intentional (e.g. artificial sweeteners) and unintentional (pesticides), suggesting that “environmental contaminants are contributing to the global epidemic of obesity”, and suggests that the review will be “helpful in elucidating their role in the obesity epidemic”. Another review focused on endocrine disrupting chemicals, but closes by saying, “public health oﬃcials should think of the obesity epidemic as a function of a multifactorial complex of events, including environmental-endocrine disruptors.” Yet another mentions “nutrient quality, stress, fetal environment and pharmaceutical or chemical exposure as relevant contributing influences.”
Canaries in the Coal Mine documents the rise in obesity in wild and captive animals and suggests that “the aetiology of increasing body weight may involve several as-of-yet unidentified and/or poorly understood factors.” What factors could these be? They list a couple: viral pathogens, epigenetic factors, and at the very end of the paper, “the collection of endocrine-disrupting chemicals (endocrine-disruptors), widely present in the environment.”
A statement from the 2nd International Workshop on Obesity and Environmental Contaminants in Uppsala, Sweden concluded that “the findings from numerous animal and epidemiological studies are consistent with the hypothesis that environmental contaminants could contribute to the global obesity epidemic.”
A National Toxicology Program workshop from 2012 suggests that “exposures to environmental chemicals may be contributing factors to the epidemics of diabetes and obesity.” They suggest that there is a link between some forms of contamination and type 2 diabetes, but overall, they say that there is still not enough research to draw firm conclusions.
Despite this interest, all the claims have been quite mild, identifying environmental contaminants as possibly being one of many factors contributing in some small way to the obesity epidemic. In contrast, we propose that the obesity epidemic is entirely driven by environmental contaminants. The entire difference in obesity between 1980 and today is attributable to one or more contaminants that we are exposed to in our food, water, and living spaces.
Still, not everyone today is obese. There are two reasons for this. First of all, even though everyone is exposed, some people are exposed to more than other people. If you live in an environment with less exposure, for example at a higher altitude, on average you will be less obese.
Some people are also less affected by these contaminants than other people, even at the same dose, and this difference is largely genetic. But even these people probably still, on average, have much more body fat than their ancestors did. Hunter-gatherers have BMIs of around 22 or 23. Civil War veterans in the 1890s had average BMIs of about 23 as well. If your BMI is higher than 23, you’re probably fatter than you would be without the action of these contaminants.
Sometimes it is these factors in combination. If you have a genetic resistance and you’re exposed to low levels of these contaminants, you’ll be much less obese than average.
3.4 Further Evidence in Favor of Contaminants
The difference in obesity rates between countries, as well as the differences between states or provinces within a country, is also the result of differences in contamination. Some of it will be genetic, but some of it is because some places are more contaminated than others.
Some of the strongest evidence for this comes from immigration. When they arrive in a new country, immigrants usually have lower obesity rates than their native counterparts do, but over time they become about as obese as the natives are. Looking at the trends, it appears that much of the effect of the contaminants occurs in the first year of exposure, though it takes 10-15 years before immigrants have obesity rates similar to the rates in the host country.
During the Cuban economic crisis known as the “Special Period”, obesity rates plummeted, from 14% obese to 7% obese. Normally this is attributed to the decrease in calorie consumption and the increase in exercise, as oil shortages led people to drive less and walk or bike more. But we know already that reducing consumption and increasing exercise have very modest effects on weight loss.
The average Cuban lost about 20 pounds in just a couple of years — even though in 1993, two years into the crisis, the average Cuban was still eating a very reasonable 2,099 calories per day.
Food was restricted, but very few people were starving. While obesity dropped from 14% to 7%, the number of people listed as “underweight” only went from 8% to 10.3% (see above). And it’s not like they were eating all that healthy — “the primary sources of energy during the crisis were sugar cane and rice.”
Rarely mentioned but particularly notable is that food imports virtually ceased during this period. If we assume that Cuban obesity was partially a result of contaminants in their food imports, this explains the data perfectly. Alternately, we can note that fertilizer and pesticide use sharply declined in this period as well, as both were normally derived from oil, which the island was now seriously lacking. These are also potential contaminants.
One surprising fact is that the most obese countries in the world by BMI are all tiny island nations in the south or central Pacific — Nauru, Tonga, Samoa, Tuvalu, Palau, the Cook Islands, and others. Depending on the year and the source, the 10 most obese nations in the world are usually small Pacific islands. Obesity rates in these countries are not merely high, they are clear outliers. The most obese mainland nations are around 35-40% obese, but these small Pacific islands have obesity rates in the range of 45-60%. Certainly this requires some sort of explanation.
To begin with, there are some reasons to suspect that this is largely an artefact. These islands all have very small populations and are genetically homogeneous, so it’s possible that much of the difference is genetic. Polynesians also appear to be slightly stouter and more muscular than other groups, which may mean that BMI is an especially bad measure for this group and leads us to slightly overestimate how obese they are. With a better measure of obesity, their obesity rates might be more similar to the rates of other very obese countries, like Kuwait and the United States.
In addition, Polynesian countries import most of their food and eat a lot of highly processed, canned meat (famously spam), which may be more contaminated than average. It’s also notable that Nauru, the most obese (61%) country in the world, has been heavily strip-mined for phosphate. This is interesting because mining is a major source of environmental contamination. For comparison, West Virginia is an obesity outlier in the United States, and it too has a long history of strip mining. In any case, this is why Nauru imports so much food — with about 80% of the island strip-mined, they can’t grow anything there. Most of these islands are not so heavily mined, of course, but this might explain why Nauru is 61% obese and Samoa is “only” 47% obese.