The Surprising Reason We May Be Thinking About Obesity All Wrong

There's no shortage of explanations for the obesity crisis: We sit at our desks, we eat too much junk, we live in sprawled-out suburbs. But what if the underlying cause is a much simpler trend?

Two-thirds of Americans are either obese or overweight. Why?

You probably think you know, because we hear a lot of explanations for the obesity crisis. It's to do with fast food sedentary lifestyles, food "deserts," not exercising enough, and a host of other reasons, from poverty to the suburban environments that discourage walking.

Roland Sturm, an economist at the Rand Corporation, thinks they're all wrong. Or, at least, that none of these explanations have much power beside an historical perspective. The most important factor, he argues, isn't how much we're sitting or pumping iron. It's how the price of food has fallen over time relative to other goods.

That may sound like an academic sort of statement, but, of course, understanding obesity trends is key to doing something about it. If access to healthy food isn't really a key reason for widening waistlines, we shouldn't be focusing on this as the solution.

In a paper written with Ruopeng An, a researcher at the University of Illinois, Sturm notes that Americans have been getting heftier since the 1950s (not just in the last decade or two) and that the increases have been consistent across demographic groups and regions. So, while black women now have higher BMI (body mass index) than Hispanic women, increases in BMI have increased together (see the chart). All women have been getting heavier, on average. Similarly, a resident of Colorado is likely to have a lower BMI than someone from Mississippi. But the rate of BMI increase has been similar across all states, irrespective of diet or exercise habits.

What this tells Sturm is that differences between people are less important than the changes that have happened to all of us. "The striking finding is the similarity of increases in BMI across groups," he says. "Targeting selected sociodemographic groups might help to reduce disparities, a laudable goal itself, but it would seem very unlikely to address the much bigger effects that have occurred over time."

The big cross-society change, Sturm finds, is the price of food. In the 1930s, we spent one quarter of disposable income on feeding ourselves. In the 1950s, it was about one fifth. Now, it's about a tenth. "The obesity epidemic has been fueled by historically low food prices relative to income," the paper says. "Americans are spending a smaller share of their income (or corresponding amount of effort) on food than any other society in history or anywhere else in the world, yet get more for it." (In Kenya or Pakistan, they still spend up to half of income, for example).

Compared with the earlier decades, we're actually exercising more and eating more fresh vegetables and fruit, Sturm says. Which should suggest that we'd be getting thinner—except we're not. We're getting fatter because we eat too much food because it's cheap—particularly "discretionary" food (cookies, sugary drinks, salty snacks) that we don't need.

Rather than promoting positive responses to obesity, like more fruit, Sturm suggests strategies to reduce caloric intake, though he doesn't think current public policy ideas will have much impact. Taxes, for example, might raise the price of bad foods. But, to be effective, they might have to reach very high levels (to correct for historic food price changes).

Ultimately, Sturm writes in an email, social pressure may be more effective. "The big drop [in tobacco use] would not have happened without changing social norms," he says. "Fifty years ago, when people came to visit, they were offered cigarettes, now that would seem to be rather inappropriate outside a few small groups."

[Image: McDonald's meal via Flickr user Happy Meal]

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  • Phillip Wilson

    Interesting article made even more interesting by the fact that we have more people on subsidized food programs in this country than ever before.

  • craigc1958

    The price of "Food" hasn't fallen, the price of toxic, sugar, salt and fat infused garbage has been artificially maintained, allowing volume sales to compensate for razor thin profit margins.

  • biker

    The cost is NOT the issue; 85% of what is sold in grocery stores is not fit to eat. If everyone thought the same way - did not put those products in their shop carts then they would stop selling them. Foods with high levels of fats, sugars and salts are addictive, simple as that. This is "Big Tobacco" all over again - but this time its "Big Food" controlling the marketplace. But don't worry if you are chronically overweight - we have electric powered shop carts now to help you get around the store - and still get all those products your body craves.

  • Jay Wiener

    Roland Stumm thinks the solution to the obesity crisis is additional social pressure? Has he been living on Mars for his entire life? The social pressure against obesity is overwhelming; it is the last socially acceptable prejudice. We correctly teach our children not to be prejudiced against people of different races, religions, or sexual preferences, but we still freely insult fat people.

    Obesity is a disease without a cure. I am a mathematician specializing in wellness. I’ve spent years studying the root causes of obesity and developing a modern, scientific algorithm to replace the obsolete body mass index (see www.weightzonefactor.com ) I also recommend the waist to hips ratio and the waist to height ratio, which give useful information. These are legitimate tools to fight obesity, but using social pressure to shame people is disgraceful

  • ukfootballcoachingnetwork

    Obesity is a disease without a cure? Eat the right things and you wont be fat, even if you do sit on your backside.

  • ukfootballcoachingnetwork

    Eat healthy, drink veg/fruit juice = lose weight, cure many many illnesses that docs only give drugs for. If every over weight person did this the obesity problem would be gone, so would drug companies profits, food companies would be forced to change their food ingredients or go bust.