obesity

What do we mean by “obesity”?

pnrj development economics, public policy , , , , , , , , , , , , , , , , ,

Nov 25 JDN 2458448

I thought this topic would be particularly appropriate for the week of Thanksgiving, since as a matter of public ritual, this time every year, we eat too much and don’t get enough exercise.

No doubt you have heard the term “obesity epidemic”: It’s not just used by WebMD or mainstream news; it’s also used by the American Heart Association, the Center for Disease Control, the World Health Organization, and sometimes even published in peer-reviewed journal articles.

This is kind of weird, because the formal meaning of the term “epidemic” clearly does not apply here. I feel uncomfortable going against public health officials in what is clearly their area of expertise rather than my own, but everything I’ve ever read about the official definition of the word “epidemic” requires it to be an infectious disease. You can’t “catch” obesity. Hanging out with people who are obese may slightly raise your risk of obesity, but not in the way that hanging out with people with influenza gives you influenza. It’s not caused by bacteria or viruses. Eating food touched by a fat person won’t cause you to catch the fat. Therefore, whatever else it is, this is not an epidemic. (I guess sometimes we use the term more metaphorically, “an epidemic of bankruptcies” or an “epidemic of video game consumption”; but I feel like the WHO and CDC of all people should be more careful.)

Indeed, before we decide what exactly this is, I think we should first ask ourselves a deeper question: What do we mean by “obesity”?

The standard definition of “obesity” relies upon the body mass index (BMI), a very crude measure that simply takes your body mass and divides by the square of your height. It’s easy to measure, but that’s basically its only redeeming quality.

Anyone who has studied dimensional analysis should immediately see a problem here: That isn’t a unit of density. It’s a unit of… density-length? If you take the exact same individual and scale them up by 10%, their BMI will increase by 10%. Do we really intend to say that simply being larger makes you obese, for the exact same ratios of muscle, fat, and bone?

Because of this, the taller you are, the more likely your BMI is going to register as “obese”, holding constant your actual level of health and fitness. And worldwide, average height has been increasing. This isn’t enough to account for the entire trend in rising BMI, but it reduces it substantially; average height has increased by about 10% since the 1950s, which is enough to raise our average BMI by about 2 points of the 5-point observed increase.

And of course BMI doesn’t say anything about your actual ratios of fat and muscle; all it says is how many total kilograms are in your body. As a result, there is a systematic bias against athletes in the calculation of BMI—and any health measure that is biased against athletes is clearly doing something wrong. All those doctors telling us to exercise more may not realize it, but if we actually took their advice, our BMIs would very likely get higher, not lower—especially for men, especially for strength-building exercise.

It’s also quite clear that our standards for “healthy weight” are distorted by social norms. Feminists have been talking about this for years; most women will never look like supermodels no matter how much weight they lose—and eating disorders are much more dangerous than being even 50 pounds overweight. We’re starting to figure out that similar principles hold for men: A six-pack of abs doesn’t actually mean you’re healthy; it means you are dangerously depleted of fatty acids.

To compensate for this, it seems like the most sensible methodology would be to figure out empirically what sort of weight is most strongly correlated with good health and long lifespan—what BMI maximizes your expected QALY.

You might think that this is what public health officials did when defining what is currently categorized as “normal weight”—but you would be wrong. They used social norms and general intuition, and as a result, our standards for “normal weight” are systematically miscalibrated.

In fact, the empirical evidence is quite clear: The people with the highest expected QALY are those who are classified as “overweight”, with BMI between 25 and 30. Those of “normal weight” (20 to 25) fare slightly worse, followed by those classified as “obese class I” (30 to 35)—but we don’t actually see large effects until either “underweight” (18.5-20) or “obese class II” (35 to 40). And the really severe drops in life and health expectancy don’t happen until “obese class III” (>40); and we see the same severe drops at “very underweight” (<18.5).
With that in mind, consider that the global average BMI increased from 21.7 in men and 21.4 in women in 1975 to 24.2 in men and 24.4 in women in 2014. That is, the world average increased from the low end of “normal weight” which is actually too light, to the high end of “normal weight” which is probably optimal. The global prevalence of “morbid obesity”, the kind that actually has severely detrimental effects on health, is only 0.64% in men and 1.6% in men. Even including “severe obesity”, the kind that has a noticeable but not dramatic effect on health, is only 2.3% in men and 5.0% in women. That’s your epidemic? Reporting often says things like “2/3 of American adults are overweight or obese”; but all that “overweight” proportion should be utterly disregarded, since it is beneficial to health. The actual prevalence of obesity in the US—even including class I obesity which is not very harmful—is less than 40%.

If obesity were the health crisis it were made out to be, we should expect that global life expectancy is decreasing, or at the very least not increasing. On the contrary, it is rapidly increasing: In 1955, global life expectancy was only 55 years, while it is now over 70.

Worldwide, the countries with the highest obesity rates are those with the longest life expectancy, because both of these things are strongly correlated with high levels of economic development. But it may not just be that: Smoking reduces obesity while also reducing lifespan, and a lot of those countries with very high obesity (including the US) have very low rates of smoking.

There’s some evidence that within the set of rich, highly-developed countries, obesity rates are positively correlated with lower life expectancy, but these effects are much smaller than the effects of high development itself. Going from the highest obesity in the world (the US, of course) to the lowest among all highly-developed countries (Japan) requires reducing the obesity rate by 34 percentage points but only increases life expectancy by about 5 years. You’d get the same increase by raising overall economic development from the level of Turkey to the level of Greece, about 10 points on the 100-point HDI scale.

 

Now, am I saying that we should all be 400 pounds? No, there does come a point where excess weight is clearly detrimental to health. But this threshold is considerably higher than you have probably been led to believe. If you are 15 or 20 pounds “overweight” by what our society (or even your doctor!) tells you, you are probably actually at the optimal weight for your body type. If you are 30 or 40 pounds “overweight”, you may want to try to lose some weight, but don’t make yourself suffer to achieve it. Only if you are 50 pounds or more “overweight” should you really be considering drastic action. If you do try to lose weight, be realistic about your goal: Losing 5% to 10% of your initial weight is a roaring success.

There are also reasons to be particularly concerned about obesity and lack of exercise in children, which is why Michelle Obama’s “Let’s Move!” campaign was a good thing.

And yes, exercise more! Don’t do it to try to lose weight (exercise does not actually cause much weight loss). Just do it. Exercise has so many health benefits it’s honestly kind of ridiculous.

But why am I complaining about this, anyway? Even if we cause some people to worry more about eating less than is strictly necessary, what’s the harm in that? At least we’re getting people to exercise, and Thanksgiving was already ruined by politics anyway.

Well, here’s the thing: I don’t think this obesity panic is actually making us any less obese.

The United States is the most obese country in the world—and you can’t so much as call up Facebook or step into a subway car in the US without someone telling you that you’re too fat and you need to lose weight. The people who really are obese and may need medical help losing weight are the ones most likely to be publicly shamed and harassed for their weight—and there’s no evidence that this actually does anything to reduce their weight. People who experience shaming and harassment for their weight are actually less likely to achieve sustained weight loss.

Teenagers—both boys and girls—who are perceived to be “overweight” are at substantially elevated risk of depression and suicide. People who more fully internalize feelings of shame about their weight have higher blood pressure and higher triglicerides, though once you control for other factors the effect is not huge. There’s even evidence that fat shaming by medical professionals leads to worse treatment outcomes among obese patients.

If we want to actually reduce obesity—and this makes sense, at least for the upper-tail obesity of BMI above 35—then we should be looking at what sort of interventions are actually effective at doing that. Medicine has an important role to play of course, but I actually think economics might be stronger here (though I suppose I would, wouldn’t I?).

Number 1: Stop subsidizing meat and feed grains. There is now quite clear evidence that direct and indirect government subsidies for meat production are a contributing factor in our high fat consumption and thus high obesity rate, though obviously other factors matter too. If you’re worried about farmers, subsidize vegetables instead, or pay for active labor market programs that will train those farmers to work in new industries. This thing we do where we try to save the job instead of the worker is fundamentally idiotic and destructive. Jobs are supposed to be destroyed; that’s what technological improvement is. If you stop destroying jobs, you will stop economic growth.

Number 2: Restrict advertising of high-sugar, high-fat foods, especially to children. Food advertising is particularly effective, because it draws on such primal impulses, and children are particularly vulnerable (as the APA has publicly reported on, including specifically for food advertising). Corporations like McDonald’s and Kellogg’s know quite well what they’re doing when they advertise high-fat, high-sugar foods to kids and get them into the habit of eating them early.

Number 3: Find policies to promote exercise. Despite its small effects on weight loss, exercise has enormous effects on health. Indeed, the fact that people who successfully lose weight show long-term benefits even if they put the weight back on suggests to me that really what they gained was a habit of exercise. We need to find ways to integrate exercise into our daily lives more. The one big thing that our ancestors did do better than we do is constantly exercise—be it hunting, gathering, or farming. Standing desks and treadmill desks may seem weird, but there is evidence that they actually improve health. Right now they are quite expensive, so most people don’t buy them. If we subsidized them, they would be cheaper; if they were cheaper, more people would buy them; if more people bought them, they would seem less weird. Eventually, it could become normative to walk on a treadmill while you work and sitting might seem weird. Even a quite large subsidy could be worthwhile: say we had to spend $500 per person per year to buy every single adult a treadmill desk each year. That comes to about $80 billion per year, which is less than one fourth what we’re currently spending on diabetes or heart disease, so we’d break even if we simply managed to reduce those two conditions by 13%. Add in all the other benefits for depression, chronic pain, sleep, sexual function, and so on, and the quality of life improvement could be quite substantial.

Why is our diet so unhealthy?

pnrj cognitive science, development economics, public policy, Uncategorized , , , , , , , , , , , , , , , ,

JDN 2457447

One of the most baffling facts about the world, particularly to a development economist, is that the leading causes of death around the world broadly cluster into two categories: Obesity, in First World countries, and starvation, in Third World countries. At first glance, it seems like the rich are eating too much and there isn’t enough left for the poor.

Yet in fact it’s not quite so simple as that, because in fact obesity is most common among the poor in First World countries, and in Third World countries obesity rates are rising rapidly and co-existing with starvation. It is becoming recognized that there are many different kinds of obesity, and that a past history of starvation is actually a major risk factor in future obesity.

Indeed, the really fundamental problem is malnutrition—people are not necessarily eating too much or too little, they are eating the wrong things. So, my question is: Why?

It is widely thought that foods which are nutritious are also unappetizing, and conversely that foods which are delicious are unhealthy. There is a clear kernel of truth here, as a comparison of Brussels sprouts versus ice cream will surely indicate. But this is actually somewhat baffling. We are an evolved organism; one would think that natural selection would shape us so that we enjoy foods which are good for us and avoid foods which are bad for us.

I think it did, actually; the problem is, we have changed our situation so drastically by means of culture and technology that evolution hasn’t had time to catch up. We have evolved significantly since the dawn of civilization, but we haven’t had any time to evolve since one event in particular: The Green Revolution. Indeed, many people are still alive today who were born while the Green Revolution was still underway.

The Green Revolution is the culmination of a long process of development in agriculture and industrialization, but it would be difficult to overstate its importance as an epoch in the history of our species. We now have essentially unlimited food.

Not literally unlimited, of course; we do still need land, and water, and perhaps most notably energy (oil-driven machines are a vital part of modern agriculture). But we can produce vastly more food than was previously possible, and food supply is no longer a binding constraint on human population. Indeed, we already produce enough food to feed 10 billion people. People who say that some new agricultural technology will end world hunger don’t understand what world hunger actually is. Food production is not the problem—distribution of wealth is the problem.

I often speak about the possibility of reaching post-scarcity in the future; but we have essentially already done so in the domain of food production. If everyone ate what would be optimally healthy, and we distributed food evenly across the world, there would be plenty of food to go around and no such thing as obesity or starvation.

So why hasn’t this happened? Well, the main reason, like I said, is distribution of wealth.

But that doesn’t explain why so many people who do have access to good foods nonetheless don’t eat them.

The first thing to note is that healthy food is more expensive. It isn’t a huge difference by First World standards—about $550 per year extra per person. But when we compare the cost of a typical nutritious diet to that of a typical diet, the nutritious diet is significantly more expensive. Worse yet, this gap appears to be growing over time.

But why is this the case? It’s actually quite baffling on its face. Nutritious foods are typically fruits and vegetables that one can simply pluck off plants. Unhealthy foods are typically complex processed foods that require machines and advanced technology. There should be “value added”, at least in the economic sense; additional labor must go in, additional profits must come out. Why is it cheaper?

In a word? Subsidies.

Somehow, huge agribusinesses have convinced governments around the world that they deserve to be paid extra money, either simply for existing or based on how much they produce. Of course, when I say “somehow”, I of course mean lobbying.

In the US, these subsidies overwhelmingly go toward corn, followed by cotton, followed by soybeans.

In fact, they don’t actually even go to corn as you would normally think of it, like sweet corn or corn on the cob. No, they go to feed corn—really awful stuff that includes the entire plant, is barely even recognizable as corn, and has its “quality” literally rated by scales and sieves. No living organism was ever meant to eat this stuff.

Humans don’t, of course. Cows do. But they didn’t evolve for this stuff either; they can’t digest it properly, and it’s because of this terrible food we force-feed them that they need so many antibiotics.

Thus, these corn subsides are really primarily beef subsidies—they are a means of externalizing the cost of beef production and keeping the price of hamburgers artificially low. In all, 2/3 of US agricultural subsidies ultimately go to meat production. I haven’t been able to find any really good estimates, but as a ballpark figure it seems that meat would cost about twice as much if we didn’t subsidize it.

Fortunately a lot of these subsidies have been decreased under the Obama administration, particularly “direct payments” which are sort of like a basic income, but for agribusinesses. (That is not what basic incomes are for.) You can see the decline in US corn subsidies here.

Despite all this, however, subsidies cannot explain obesity. Removing them would have only a small effect.

An often overlooked consideration is that nutritious food can be more expensive for a family even if the actual pricetag is the same.

Why? Because kids won’t eat it.

To raise kids on a nutritious diet, you have to feed them small amounts of good food over a long period of time, until they acquire the taste. In order to do this, you need to be prepared to waste a lot of food, and that costs money. It’s cheaper to simply feed them something unhealthy, like ice cream or hot dogs, that you know they’ll eat.

And this brings me to what I think is the real ultimate cause of our awful diet: We evolved for a world of starvation, and our bodies cannot cope with abundance.

It’s important to be clear about what we mean by “unhealthy food”; people don’t enjoy consuming lead and arsenic. Rather, we enjoy consuming fat and sugar. Contrary to what fad diets will tell you, fat and sugar are not inherently bad for human health; indeed, we need a certain amount of fat and sugar in order to survive. What we call “unhealthy food” is actually food that we desperately need—in small quantities.

Under the conditions in which we evolved, fat and sugar were extremely scarce. Eating fat meant hunting a large animal, which required the cooperation of the whole tribe (a quite literal Stag Hunt) and carried risk of life and limb, not to mention simply failing and getting nothing. Eating sugar meant finding fruit trees and gathering fruit from them—and fruit trees are not all that common in nature. These foods also spoil quite quickly, so you eat them right away or not at all.

As such, we evolved to really crave these things, to ensure that we would eat them whenever they are available. Since they weren’t available all that often, this was just about right to ensure that we managed to eat enough, and rarely meant that we ate too much.

 

But now fast-forward to the Green Revolution. They aren’t scarce anymore. They’re everywhere. There are whole buildings we can go to with shelves upon shelves of them, which we ourselves can claim simply by swiping a little plastic card through a reader. We don’t even need to understand how that system of encrypted data networks operates, or what exactly is involved in maintaining our money supply (and most people clearly don’t); all we need to do is perform the right ritual and we will receive an essentially unlimited abundance of fat and sugar.

Even worse, this food is in processed form, so we can extract the parts that make it taste good, while separating them from the parts that actually make it nutritious. If fruits were our main source of sugar, that would be fine. But instead we get it from corn syrup and sugarcane, and even when we do get it from fruit, we extract the sugar instead of eating the whole fruit.

Natural selection had no particular reason to give us that level of discrimination; since eating apples and oranges was good for us, we evolved to like the taste of apples and oranges. There wasn’t a sufficient selection pressure to make us actually eat the whole fruit as opposed to extracting the sugar, because extracting the sugar was not an option available to our ancestors. But it is available to us now.

Vegetables, on the other hand, are also more abundant now, but were already fairly abundant. Indeed, it may be significant that we’ve had enough time to evolve since agriculture, but not enough time since fertilizer. Agriculture allowed us to make plenty of wheat and carrots; but it wasn’t until fertilizer that we could make enough hamburgers for people to eat them regularly. It could be that our hunter-gatherer ancestors actually did crave carrots in much the same way they and we crave sugar; but since agriculture we have no further reason to do so because carrots have always been widely available.

One thing I do still find a bit baffling: Why are so many green vegetables so bitter? It would be one thing if they simply weren’t as appealing as fat and sugar; but it honestly seems like a lot of green vegetables, such as broccoli, spinach, and Brussels sprouts, are really quite actively aversive, at least until you acquire the taste for them. Given how nutritious they are, it seems like there should have been a selective pressure in favor of liking the taste of green vegetables; but there wasn’t. I wonder if it’s actually coevolution—if perhaps broccoli has been evolving to not be eaten as quickly as we were evolving to eat it. This wouldn’t happen with apples and oranges, because in an evolutionary sense apples and oranges “want” to be eaten; they spread their seeds in the droppings of animals. But for any given stalk of broccoli, becoming lunch is definitely bad news.

Yet even this is pretty weird, because broccoli has definitely evolved substantially since agriculture—indeed, broccoli as we know it would not exist otherwise. Ancestral Brassica oleracea was bred to become cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard greens, savoy, kohlrabi and kai-lan—and looks like none of them.

It looks like I still haven’t solved the mystery. In short, we get fat because kids hate broccoli; but why in the world do kids hate broccoli?