Don't blame fast-food restaurants for why America seems so supersized. This new economic study from Northwestern University and UC Berkeley seems to disprove the the common nutritional myth:
The results find no evidence of a causal link between restaurants and obesity, and the estimates are precise enough to rule out any meaningful effect. Analysis of food intake micro data suggests that although consumers eat larger meals at restaurants than at home (even after accounting for selection), they offset these calories at other times of day. We conclude that public health policies targeting restaurants are unlikely to reduce obesity but could negatively affect consumer welfare.
Although restaurants conveniently deliver calories at a low marginal cost, they are only one source among many. While taxing restaurant meals might cause obese consumers to change where they eat, our results suggest that a tax would be unlikely to affect their underlying tendency to overeat. The same principle would apply to other targeted obesity interventions as well. For example, two recent large-scale, multi-state randomized trials of school-based programs that improved the nutritional content of cafeteria meals found no effect on student weight (Nader et al. 1999; Caballero et al. 2003). One principal investigator noted, in retrospect, that the intervention could not control what the children ate outside of school (Kolata 2006). Future research and policy proposals may find greater success if they are designed to account for the optimizing behavior of the targeted subjects.