Why beverage taxes won't reduce obesity

By Charles L. Baum

Mayor Nutter's proposed soda tax didn't end up going anywhere, but it did contribute to an unfortunate myth: the notion that any class of food or beverage is particularly fattening.

That was the stated motivation for Nutter's proposal. A ranking city health official declared that "there's good evidence for sugary drinks' being a major culprit in the increase in obesity." And public-health activists claimed that soft drinks contribute disproportionately to the government's obesity-related costs.

However, a new study I conducted with Lehigh University's Shin-Yi Chou suggests that the dynamics of obesity are far more complex than the soda critics suggest.

Using government body mass index data spanning a 27-year period, we analyzed multiple potential factors in the recent rise in American obesity, including food prices, physical activity at work, restaurant prevalence, urbanization, employment, and cigarette smoking.

Based on the current conventional wisdom, you might guess that food prices or restaurant prevalence would affect obesity most. But among the variables we studied, the most significant factor in BMI increases was the decline in smoking. This makes sense: Cigarettes are an appetite inhibitor.

This single greatest factor, however, still accounted for a very small share of the rise in obesity, about 2 percent.

Obesity is also linked to urban sprawl, not surprisingly: More driving means less walking. Occupational fitness is another factor: More time sitting at a desk means fewer calories burned.

Neither of these plays a large role either, though. Urban sprawl accounted for only 0.7 percent of the rise in BMI, occupational fitness 0.5 percent. And fast-food prices, grocery prices, and restaurant prevalence were all statistically insignificant.

In other words, there's no one or two central causes of rising obesity.

Philadelphia officials aren't wrong to be concerned about obesity. The obesity rate citywide is 40 percent, and 17 percent among high school students, according to Temple University.

But our results indicate that antiobesity public policies are generally of limited utility. Besides soda, activists have accused corner stores and fast food of contributing to a "toxic food environment." Yet fast-food prices, grocery prices, and restaurant prevalence all registered statistically insignificant effects in our study.