In a new paper from the National Bureau of Economic Research, researchers at U.C.-Berkeley and Columbia report that the obesity rate among ninth-graders whose schools are very close to fast food restaurants (within one-tenth of a mile) is about 5 percent higher than the obesity rate among ninth-graders whose schools are a bit further away (within a quarter mile). Columbia economist Janet Currie and her colleagues argue that the difference, amounting to 1.7 percentage points, is probably due to the easy availability of cheap, calorie-dense food (although they concede that it could be caused by unmeasured variables related to both greater demand for fast food and higher obesity rates). At the same time, they find that the proximity of fast food restaurants does not seem to play a significant role in weight gain among pregnant women, possibly because they can get around more easily than carless high school students. "Our results suggest that a ban on fast foods in the immediate proximity of schools could have a sizeable effect on obesity rates among affected students," Currie et al. write. "However, a similar attempt to reduce access to fast food in residential neighborhoods would be unlikely to have much effect on adult consumers."

One reason I'm leery of proposals to ban soda and "junk food" from schools (as California, the source of the student data for this study, has done) is that I suspect such policies, once they prove ineffective, will be followed by restrictions that impinge on the rights of adults. Currie et al. are not the first researchers to suggest fast-food-free zones around schools. I'm not sure how big an impact the 500-foot rule suggested by their study would have on the choices available to adults, but judging from the experience with gun-free, drug-free, and sex-offender-free zones, anything like a 1,000-foot rule would be prohibitive for fast food restaurants in many cities. 

Here is the Berkeley press release about the study. Here is the Los Angeles Times story.