Is the obesity epidemic a mystery? Part 1

While browsing the always excellent and highly recommended Marginal Revolution blog, I came across an interesting series of posts on the “Mystery of the Obesity Epidemic“.

It’s a well-researched series of posts, with a lot of interesting facts and statistics.

It comes to some rather strange conclusions, however.

Calories Do Count and Diets Do Work

One of the supposed unexplainable mysteries is the fact that “Diets Don’t Work”.

This is not exactly true though. Whether it’s paleo, vegan, keto, South Beach, low fat, cabbage soup, or simply counting calories, people can and do lose weight if they stick to any kind of dietary restriction.

Indeed, in the article the author notes:

Most diets lead to weight loss of around 5-20 lbs, with minimal differences between them. Now, 20 lbs isn’t nothing, but it’s also not much compared to the overall size of the obesity epidemic. And even if someone does lose 20 lbs, in general they will gain most of it back within a year.

Yes, most people tend to gain all the weight back, but this is not because the diets stop working, but because the people stop following the diets.

In part ii of the series, the author calls into question the calories in vs calories out theory.

It’s not that calories don’t matter at all. People who are on a starvation diet of 400 calories per day will lose weight, and as we will see in this section, people who eat hundreds of calories more than they need will usually gain weight. The problem is that this ignores how the body accounts for the calories coming in and going out. If you don’t eat enough, your body finds ways to burn fewer calories. If you eat too much, your body doesn’t store all of the excess as fat, and compensates by making you less hungry later on.

So far, so good. Can’t argue with any of that. Neither losing weight nor gaining weight are easy. The body is excellent at homeostasis. Changing your weight in either direction requires a long and sustained calorie imbalance.

The author notes that while it’s hard to get reliable figures, most research indicates that on average people (in the US) now consume 300-400 additional calories per day than they did in the 1970s.

They then go on to describe a number of studies and anecdotes where people gain weight while on a high-calorie diet, then lose the weight again when they go back to a normal diet:

The great-grandaddy of these studies is the Vermont prison experiment, published in 1971. Researchers recruited inmates from the Vermont State Prison, all at a healthy weight, and assigned some of them to eat enormous amounts of food every day for a little over three months. How big were these meals? The original paper doesn’t say, but later reports state that some of the prisoners were eating 10,000 calories per day.

On this olympian diet, the prisoners did gain considerable weight, on average 35.7 lbs (16.2 kg). But following the overfeeding section of the study, the prisoners all rapidly lost weight without any additional effort, and after 10 weeks, all of them returned to within a couple pounds of their original weight. One prisoner actually ended up about 5 lbs (2.3 kg) lighter than before the experiment began!

Inspired by this, in 1972, George Bray decided to conduct a similar experiment on himself. He was interested in conducting overfeeding studies, and reasoned that if he was going to inflict this on others, he should be willing to undergo the procedure himself. First he tried to double each of his meals, but found that he wasn’t able to gain any weight — he simply couldn’t fit two sandwiches in his stomach at every sitting.

He switched to energy-dense foods, especially milkshakes and ice cream, and started eating an estimated 10,000 calories per day. Soon he began to put on weight, and gained about 22 lbs (10 kg) over 10 weeks. He decided this was enough and returned to his normal diet. Six weeks later, he was back at his original weight, without any particular effort.

In both cases, you’ll notice that even when eating truly stupendous amounts of food, it actually takes more time to gain weight than it does to lose it. Many similar studies have been conducted and all of them find basically the same thing — check out this recent review article of 25 studies for more detail.

Overfeeding in controlled environments does make people gain weight. But they don’t gain enough weight to explain the obesity epidemic. If you eat 10,000 calories per day, you might be able to gain 20 or 30 pounds, but most Americans aren’t eating 10,000 calories per day.

The logical conclusion to these studies, however, is that over-consuming calories clearly does lead to weight gain.

This is simply the other side of the same coin to the fact that people lose weight when they’re on a low-calorie diet, then gain it back when they return to a high-calorie diet.

Again, really nothing surprising or mysterious here – if you consistently overeat calories you will most likely gain weight, and if you consistently undereat calories and you will most definitely lose weight.

Do you have to consume 10,000 calories a day to become obese? I’d agree that seems like quite a lot.

We don’t have data on the exact numbers of calories consumed by the prisoners, but 10,000 was certainly not their average daily calorie consumption, rather an upper limit. Perhaps it was just one prisoner on one day. We don’t have the numbers unfortunately. Here is the methodology from the study:

Subjects. All subjects were inmates of the Vermont State Prison who volunteered for the study. They were selected so as to exclude those with a history or family history of diabetes mellitus, obesity, or other metabolic and nutritional disorders. The seven volunteers ranged in age from 20 to 30 yr and in normal body weight from 61 to 84 kg, as indicated in Table I.

All subjects followed normal prison routine during the entire period of the study, except that they ate meals together as a group in a dining room set aside for the purpose and during the period of weight gain they reduced their physical activity. The caloric content and composition of their diet was estimated from standard dietary tables. The quantity of food ingested by each individual at each meal was carefully recorded. During an initial 6 wk study period sufficient calories were provided to maintain constant body weight (base line weight).

In five of the seven subjects this initial period was followed by a 3-4 month period of high
caloric intake to produce weight gain. After desired or maximum obtainable weight was reached, each of these five subjects ingested sufficient numbers of calories to maintain
constant weight during the second study period (peak weight), which was of 10 wk duration. The final phase of the study began after a period in which caloric restriction and increased activity induced loss of weight to original levels. During the final study period sufficient calories were provided to maintain constant normal body weight (reduced base line). The body weight of the two control subjects was maintained at a constant level throughout all three study periods. Determination of total body fat, adipose cell size, and adipose cell number was made on each patient during each of these study periods.

Experimental Obesity in Man: Cellular
Character of the Adipose Tissue (PDF)
LESTER B. SALANS, EDWARD S. HORTON, and ETHAN A. H. SIMS

Wow, shocking results, what a crazy mystery this all is! Oh, wait, no…

When the participants stopped exercising and started overeating they gained weight. All of them.

When they then followed a program of diet and exercise they lost all of the weight again. All of them.

OK, there were only 5 participants in the study, but the results are highly unsurprising and I fail to see how they could be interpreted as contradicting the calories in vs calories out theory, or indicating that diets and exercise don’t work.

Overfeeding in controlled environments does make people gain weight. But they don’t gain enough weight to explain the obesity epidemic. If you eat 10,000 calories per day, you might be able to gain 20 or 30 pounds, but most Americans aren’t eating 10,000 calories per day.

Even if the participants were eating 10,000 calories per day (which they almost certainly weren’t), this doesn’t prove that weight gain is only possible under such circumstances. On average, the participants gained around 14kg over a 3 month period. That’s a crazy amount of weight (just over 2 stone or 30lbs) in a very short period of time. Yes, the obesity epidemic may have happened rapidly on the timescale of the human species, but it didn’t happen in just 3 months.

Adults tend to gain weight progressively through middle age. Although the average weight gain is 0.5 to 1 kg per year, this modest accumulation of weight can lead to obesity over time.

Strategies to Prevent Weight Gain Among Adults
Susan Hutfless et al

The Problem with Averages

I consider myself an average man, except in the fact that I consider myself an average man

Michel de Montaigne

I also consider myself an average man, except in my energy intake and expenditure.

As noted in the article, the figures for average calorie consumption are pretty speculative. It is however generally accepted that calorie consumption has increased. As noted before, the best estimates range between a 300-400 average daily increase since the 70s (Though others say up to 700). The author seems to think this isn’t very much, and indeed compared to 10,000 calories per day it sounds rather trifling.

But an average increase of 400 calories doesn’t mean that these calories are evenly distributed.

Not everyone is overconsuming calories. Most people at a healthy BMI will be consuming the same or fewer calories than someone in the 70s (presuming most will have similar or lower energy expenditure due to more sedentary lives in general). This means that for the average to increase by 3-400, those that are overconsuming calories must be doing so by more than the average.

I.e. if there were two people with an average daily consumption of 2400kCal and one is consuming 2000kCal, the other must be consuming 2800kCal.

The same is true for energy expenditure. Again, the data is sketchy.

The general consensus is that activity levels have decreased, but then there are some conflicting reports that gym use and exercise uptake are higher than ever.

In the article the author states:

People are exercising more today than they were 10 or even 20 years ago. Contrary to stereotypes, more than 50% of Americans meet the HHS guidelines for aerobic exercise. But obesity is still on the rise.

These figures come from the National Health Interview Survey (pdf) and look highly dubious. The results can be seen on page 42. There are large ratchet-like increases between 2008-2009, then again between 2016-2017. This looks to me more like some kind of effect from the way the data was collected or processed, rather than real increases in leisure activity time.

Even if the data is correct, it still leaves us with almost half of the population getting less than the minimum recommended level of exercise, which is itself pretty low. It also doesn’t account for changes in physical activity in the workplace or NEPA which have also almost certainly decreased since the 70s.

I’m still failing to find any shocking or mysterious results in any of this data.

It’s all perfectly consistent with the theory that people are eating more calories and doing less physical activity.

What has changed?

Now, to be fair to the article, there is something going on.

On the individual level, obesity is not a mystery, it is very simple.

People gain weight when they consistently consume more calories than they burn.

This process can be reversed by consistently restricting calories to create an energy deficit.

The puzzle is why are more and more people overconsuming calories and becoming overweight and obese than ever before in history?

According to part iii:

Based on the evidence, we’re looking for a factor that:

1. Changed over the last hundred years
2. With a major shift around 1980
3. And whatever it is, there is more of it every year
4. It doesn’t affect people living nonindustrialized lives, regardless of diet
5. But it does affect lab animals, wild animals, and animals living in zoos
6. It has something to do with palatable human snackfoods, unrelated to nutritional value
7. It differs in its intensity by altitude for some reason
8. 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.

Really? No other account? Hmm.

Before looking into other possible accounts in part 2, let’s address the errors and contradictions in the above points.

1 & 2: Something changed in the last hundred years with a major shift around 1980?

This is based on the data from this graph:

The problem with looking at rates of obesity, rather than say BMI, is that the classification of obesity is an arbitrary cut off of 30. Here’s a graph that simply plots average BMI over time from 1975-2016:

1980 starts to look a little less significant.

Unfortunately, we don’t have very reliable data to see exactly when this trend started. What we do know is that overweight and obesity are not a new phenomenon. There were overweight and obese people in the 19th century, 18th century, all the way back to as far as 30,000 years ago. There are theories that the trend actually started as far back the end of the 19th Century.

Now don’t get me wrong, I am not an obesity epidemic denier. There are most certainly more overweight and obese people now than ever before in history. What isn’t clear is exactly when this trend started.

3. Whatever it is there’s more of it every year?

Rates of obesity have been steadily increasing since good records began. I think it’s a mistake to look for “A factor”. I think it’s very unlikely that there’s a single “It” to be discovered.

Here’s just one possible “it factor” that’s been increasing every year that could plausibly be connected, but there are many many others – Highly palatable processed food, car ownership, hours of TV watched and video games played, etc.

And why does there have to be more of it? Could something be decreasing that’s driving the rate of obesity up? Just to be clear, I’m not suggesting that falling rates of smoking are driving the obesity epidemic. Take this more as both a “correlation does not imply causation” reminder, and also that many factors are likely involved. Does anyone think that smoking rates decreased due to one single factor of which there was more/less of every year?

4. It doesn’t affect people living nonindustrialized lives, regardless of diet

Here the author is referring to the fact that traditional hunter-gatherer societies do not suffer from overweight or obesity, despite eating a very wide range of diets – some high in fat, some high in sugar, some nearly all meat, some nearly all vegan. I’ve written before about the problems with the Paleo diet science so won’t go too in-depth with the many issues here.

What should be noted, however, is that what all of their diets have in common is an absence of highly palatable processed foods and that when these foods are introduced traditional peoples rapidly begin to gain weight and become overweight and obese. It is not, therefore “regardless of diet”.

5. It does affect lab animals, wild animals, and animals living in zoos

Lab animals and wild animals are becoming more obese because they are exposed to the same environmental contaminants that we are. 

There is no evidence for this. Researchers were actually struggling to get lab rats to overeat and get fat until someone tried adding highly palatable processed foods from the lab cafeteria to the standard chow.

Examples of these foods include cakes, sweet biscuits, and high-fat savory snacks (such as processed meats, cheese and chips). It reliably promotes hyperphagia and rapid weight gain in rodents. The key features of the model are the provision of a variety of highly palatable foods, designed to simulate the modern food environment.

Palatable Western-style Cafeteria Diet as a Reliable Method for Modeling Diet-induced Obesity in Rodents

Wild animals get fat when they scavenge leftover highly palatable processed foods.

How about zoo animals? Zoo animal obesity is not something I’ve ever researched, but a quick google brings up more unsurprising results – yes folks, it’s diet and exercise again!

He missed pet cats and dogs from this list, which are also getting overweight and obese. It must be all the video games they play nowadays! When I was a kid the dogs and cats used to play outside. Or maybe something to do with the highly palatable processed foods we feed them?

6. It has something to do with palatable human snack foods, unrelated to nutritional value

As you may have gathered by now, I am sympathetic to the idea that it has something to do with highly palatable processed foods.

I’d disagree with the “unrelated to nutritional value” part though. An important part of making food highly palatable is high nutrient density.

I don’t think this is the only factor, but it certainly appears to play a highly significant role.

7. It differs in its intensity by altitude for some reason

The inverse relationship between altitude and obesity prevalence is certainly interesting and warrants further research.

The author however goes onto state categorically that this relationship is causal and that:

Obesity is less common at high altitudes because of the watershed.

Er, really? Their evidence for this is that obesity rates are higher in states where the groundwater has covered more distance, and therefore collected more contaminating chemicals.

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.

Damn those confusing outliers. But don’t let contradictory evidence get in the way of a good theory!

This map of minimum wage rates also corresponds pretty well however as does this one which shows percentage of population that commute by car, and a map of population density:

This last map shows the same-sex marriage laws. Yes, there are some confusing outliers in this one…

Needless to say, I’m not convinced by the contaminated groundwater theory just yet, I’d want to see some supporting evidence first.

8. It appears to have nothing to do with our diets

Finally, no diet will reliably help because obesity isn’t caused by a bad diet and can’t be cured by a good one.

Except, that it clearly has everything to do with our diets. As we’ve seen above people gain weight from overconsuming calories, and sticking to any number of different diets will result in weight loss.

The only mystery is why are more and more people now consistently overconsuming calories than ever before?

In part 2 I’m going to further explore the possible role of highly palatable processed foods as a major driving force behind the obesity epidemic, then look at a number of other factors that could well also be significant contributors.