Here's a fact that shows just how quickly obesity has taken over America: In 1990, no state had an obesity prevalence of 15 percent or more. By 2010, no state was less than 20 percent obese.
Adult Obesity Prevalence in 1990 and 2010
But what's driving the epidemic? We have no answers, only theories. Some studies say it's food deserts; others say it's desk jobs. Some even claim that it's the decline in smoking, since tobacco suppresses appetite.
Along with three other researchers, Charles Courtemanche, an assistant professor of economics at Georgia State University, analyzed a number of these theories for a recent study.
Courtemanche realized that a lot of past studies came to conclusions like, "the increasing popularity of driving to work is correlated with the rise of obesity." But he wasn't sure what, specifically, was having the greatest effect on obesity's rise.
He gathered 27 things he thought might be contributing to obesity—everything from working hours to exercise trends to gas prices—and put them in what he calls a "statistical horserace." Essentially, he took all the studies that associated some factor with obesity and saw what would happen if he held everything else constant, like demographic or economic changes. (For example, he told me, "If you're just looking at cigarette prices, was it really cigarette prices, or is it just that they're related to food prices and gas prices? It's controlling for everything together.)