Sunday, February 14, 2010

flipping the question

Image courtesy of the CDC.

Unless you've been living in a box for the past decade, you know that obesity rates are skyrocketing. In 1990, roughly 12% of Americans were obese, meaning that their BMI was greater than 30. By 2004, nearly a quarter of Americans were obese* (Harper and Lynch 2007).

It's customary in the blogosphere and media to blame rising obesity on two factors: lousier diets and lazier people. The problem with the "lazy people" explanation is that the data don't really bear it out. Indeed, the percentage of people who are physically inactive declined, from 30% in 1990 to 23% in 2004.

Granted, the measure of physical inactivity -- no leisure-time physical activity for a month -- isn't perfect. "Leisure time" physical inactivity ignores on-the-job physical activity. Anyone who has scraped the exterior of a house or waited tables for an 8-hour shift knows that the work can be physically exhausting. It's also not clear how survey respondents are interpreting the question about physical activity: does walking the dog count? or does it have to entail a trip to the gym in order to ride the elliptical to nowhere."

These errors can affect trends, depending on how societal definitions of physical activity change over time. It could be, for example, that the late 1990s push to redefine walking as a form of exercise means that fewer people reported inactivity in 2004 than in 1990, even if there was no change in the underlying behavior.

But if we take the data on their own terms, we're left with an even thornier problem than the "lazy people" camp acknowledges. If they were right, we should see a decrease, or at least leveling off, of obesity rates. It ain't happening. Changes (for the better) in physical activity have not been sufficient to offset changes (for the worse) in either the amount or the type of food Americans eat.

I don't know what the solution is, but I do know that calling people lazy isn't the answer. Maybe we should stop subsidizing corn growers and start subsidizing broccoli farmers.

I'm not kidding.

be strong//

*yeah, yeah, I know BMI is just a ratio of weight to height, and hence differentiate between "good" weight (muscle, bone) and "bad" weight (fat). Yeah, yeah, I know that a lot of bodybuilders would be classified as obese, according to BMI. But, let's face it, there aren't enough budding Arnolds out there to account for the rise in obesity.

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