Obesity has been on the rise in the United States for decades. Between 1990 and 2010, for example, the average body-mass index in the U.S. increased from about 26 to about 29, corresponding to a 20-pound gain for average-height Americans. Researchers have long suspected economic factors played a role in that jump. A new comprehensive study from the National Bureau of Economic Research confirms that story, but with a twist: The expansion of restaurants and warehouse stores like Costco seems to be behind our expanding waistlines as well.
As is often the case in such studies, much of the challenge NBER economists Charles Courtemanche, Joshua Pinkston, Christopher Ruhm, and George Wehby faced in reaching that conclusion lay in gathering and collating the relevant data. In their case, that meant merging individual health data from the Centers for Disease Control and Prevention with state-level economic indicators and business data from the Council for Community and Economic Research, the Bureau of Labor Statistics's Quarterly Census of Employment and Wages, and the U.S. Census Bureau. The team also drew on data they'd collected in previous work to map out the locations of four big-box retailers: Walmart Supercenters, Sam's Club, Costco, and BJ's Wholesale Club.
More surprising than what influenced BMI was how much of its rise could be explained by economic factors alone—roughly 43 percent, the researchers estimate.
Digging into that mass of data revealed that a variety of economic factors play a role in determining BMI. Intuitively, higher densities of restaurants and warehouse stores like Costco were associated with higher BMIs, while higher densities of supermarkets and gyms were correlated with lower BMIs. Meanwhile, higher alcohol prices and a lower proportion of blue-collar workers in a state appeared to reduce BMI.
More surprising than what influenced BMI was how much of its rise could be explained by economic factors alone—roughly 43 percent, the researchers estimate, and that effect is "almost entirely driven by changes in the variables related to the costs of calories," they write. The proliferation of big-box warehouse retailers such as Costco accounts for about 17 percent of the increase in BMI since 1990, the team estimates, with restaurant expansion accounting for another 12 percent.
Intriguingly, the increasing availability of warehouse stores and restaurants also seems to have triggered a growing number of weight loss attempts over the years. That, the authors indicate, may be related to difficulty balancing short-term pleasure versus long-term goals. "Discount big-box grocers may trigger impulses that lead to 'mistakes,'" which in turn trigger attempts to shed pounds, they write.
Though it's impossible to say for sure using survey data, a variety of analyses on the results suggest the arrival of warehouse stores and restaurants probably caused the increase in BMI over the last two decades. The possibility remains, however, that such businesses simply moved to where people ate the most, or perhaps that the two factors fed off of each other. "Future research should push further" to establish which it is, the team writes.