This paper investigates the health consequences of proximity to fast food for two
vulnerable groups: young teens and pregnant women. The focus on very close distances
and the presence of a large array of controls alleviates issues of endogenous fast-food
placement. Our results point to a significant effect of proximity to fast food restaurant on
the risk of obesity, though the magnitude of the effect is very different for school children
and adults. The presence of a fast food restaurant within a tenth of a mile of a school is
associated with at least a 5.2 percent increase in the obesity rate in that school (relative to
the presence at .25 miles). Consistent with highly non-linear transportation costs for
school children, we find no evidence of an effect at .25 miles and at .5 miles. The effect
at .1 miles distance is equivalent to an increase in daily caloric consumption of 30 to 100
calories due to proximity of fast-food. The effect for pregnant women is quantitatively
smaller and more linear in distance. A fast food restaurant within half a mile of a
residence results in a 1.6 percent increase in the probability of gaining over 20 kilos. This
effect increases to a 5.5 percent increase when a fast-food is within .1 miles from the
residence of the mother. The effect at .5 miles translates into a daily caloric intake of 1 to
4 calories, two orders of magnitudes smaller than for school children.
The quantitative difference in the impact of fast-food between school children and
mothers has policy implications. To the extent that the estimates for mothers are
representative of the estimates for adults, attempts to limit the presence of fast-food
throughout residential areas are unlikely to have a sizeable impact on obesity. Instead,
narrower policies aimed at limiting access to fast food could have a sizable impact on
populations with limited ability to travel, such as school children.
Using our estimates, we can do a calibration of the impact of fast-food penetration
on school children and women. Taking into account that only about 6.7 percent of
schools (in our sample) have a fast-food restaurant within .1 miles, fast-food restaurants
near schools can be responsible for only 0.5 percent of the increase in obesity over the
last 30 years among 9th graders.23 This is because, although having a fast food restaurant
very close to the school has a large effect on affected ninth graders, relatively few
children have a restaurant so close. Still, the results suggest that measures designed to
limit access to fast food among teenagers more broadly (such as restrictions on
advertising to children, or requirements to post calorie counts) could have a beneficial
effect.24
For mothers, if we assume that the effect of fast-food on weight gain for pregnant
mothers is the same as for non-pregnant women, then fast-food restaurants near a
women’s residence could be responsible for about 2.7 percent of the increase in weight in
the last ten years among women.25 While we cannot explain a large share of the changes
in obesity and weight in either case, one explanation of the larger fraction explained for
mothers is that the effect is found at a longer distance (.5 miles); the second is the longer
assumed exposure time. If, for example, having a fast food restaurant near the school
continued to influence children’s eating habits throughout highschool, then the
cumulative effect for teens might well be larger than that estimated here.
These findings add new evidence to the debate about the impact of fast-food on
obesity by providing credible evidence on magnitudes of the effect of fast-food. Still,
this research leaves several questions unanswered. We cannot speculate about the
generalizability of our research to other samples; it is possible that adolescents and
pregnant women are uniquely vulnerable to the temptations of fast food. In addition, our
research cannot distinguish between a rational price-based explanation of the findings
and a behavioral self-control-based explanation. Finally, since fast food is ubiquitous in
America, we cannot study the impact of fast-food entry in a society where fast food is
scarce. We hope that some of these questions will be the focus of future research.