Sprawling Waistlines

When your city spreads out, so does your paunch – at least according to new work from the NBER stable. Their IV strategy seems credible, suggesting that the relationship is probably causal.

Effects of Urban Sprawl on Obesity (unstable ungated, stable gated)
Zhenxiang Zhao and Robert Kaestner

In this paper, we examine the effect of changes in population density–urban sprawl–between 1970 and 2000 on BMI and obesity of residents in metropolitan areas in the US. We address the possible endogeneity of population density by using a two-step instrumental variables approach. We exploit the plausibly exogenous variation in population density caused by the expansion of the U.S. Interstate Highway System, which largely followed the original 1947 plan for the Interstate Highway System. We find a negative association between population density and obesity and estimates are robust across a wide range of specifications. Estimates indicate that if the average metropolitan area had not experienced the decline in the proportion of population living in dense areas over the last 30 years, the rate of obesity would have been reduced by approximately 13%.