Fast food outlets and obesity: what is the evidence?

Several local authorities in Britain have introduced ‘zoning laws’ to restrict fast food outlets within a certain distance of schools. Public Health England, the British Medical Association and the Mayor of London have all endorsed this policy as a way of tackling childhood obesity. Standard economic theory suggests that restricting supply by law leads to higher prices, poorer quality and reduced choice for consumers. Fast food zoning bans effectively protect incumbent businesses from competition at the expense of the public. These anti-competitive measures are said to be justified on public health grounds to tackle childhood obesity. This report looks at the empirical literature to see whether this is true. We identified 74 studies published over a period of fifteen years which look at the relationship between the density and proximity of fast food outlets and the prevalence of obesity. Of the studies, only fifteen (20%) found a positive association between the proximity and/or density of fast food outlets and obesity/body mass index. Forty-four (60%) found no positive association, of which eleven (15%) found evidence that living near a fast food outlet reduced the risk of putting on weight. Fifteen (20%) produced a mix of positive, negative and (mostly) null results, which, taken together, point to no particular conclusion. The evidence that fast food availability causes obesity among children is even weaker. Of the 39 studies that looked specifically at children, only six (15%) found a positive association while twenty-six (67%) found no effect. Seven (18%) produced mixed results. Of the studies that found no association, five (13%) found an inverse relationship between fast food outlets and childhood obesity. Two-thirds of the studies found no evidence for the hypothesis that living near fast food outlets increases the risk of childhood obesity and there are nearly as many studies suggesting that it reduces childhood obesity as there are suggesting the opposite. Studies which suggest that living near a fast food outlet increases the risk of obesity are outnumbered 3 to 1 by those which find no such association. For childhood obesity, this ratio rises to 4 to 1. The belief that restricting the availability of fast food will reduce obesity in children or adults is based on assumptions that are not supported by an extensive body of evidence.

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