Newswise — Big-box retailers Costco, Sam’s Club, BJ’s Wholesale and Walmart, along with full-service and fast-food restaurants, are key contributors to the nation’s obesity epidemic, according to research by a health economist in the Andrew Young School of Policy Studies at Georgia State University. Americans now live near an abundance of cheap and readily available food from a variety of sources, report Georgia State health economist Charles Courtemanche and his colleagues in a new study. A closer look reveals little difference among the sources themselves. “People are doing a lot of eating,” said Courtemanche, an assistant professor in the Andrew Young School of Policy Studies. “But as economists, we know people’s preferences don’t change overnight, so the steady rise since 1980 must involve their incentives to eat.” This question led Courtemanche and his colleagues to build a comprehensive economic model of body weight and 27 state-level variables they categorized as general economic conditions (unemployment and income) and labor supply, as well as the monetary or time costs associated with calorie intake (food prices, retail presence), physical activity (gasoline prices, fitness centers) and smoking. Titled “Can Changing Economic Factors Explain the Rise in Obesity?” their research was published by the National Bureau of Economic Research last week. “Changes in variables related to calorie intake collectively explain 37 percent of the rise in body mass index (BMI) rates and 43 percent of the rise in obesity,” Courtemanche said. “And our data show that the pervasive presence of supercenters, warehouse clubs and restaurants are responsible for most of these gains.” Fitness centers and rising gas prices were found to work against the rise in BMI. The research suggests these effects are not the same for everyone. “The greatest rise in weight is concentrated among people already at risk for obesity,” Courtemanche said. “And their response to the variables related to calorie intake can help us understand why BMI rates are changing.” The shrinking proportion of blue-collar workers and rise in food stamp benefits also contribute to the nation’s rising obesity, the data suggest this effect is not due to differences in on-the-job physical activity. “The best explanation for the difference between these workers, outside of physical movement, is time flexibility,” Courtemanche said. “White-collar workers have the flexibility to graze all day at their desks, and they can take lunch out. It all points to caloric intake.” The new report builds on additional new research by Courtemanche that suggests that an individual’s level of patience, also known as time preference, predicts how susceptible he or she may be to weight gain. The Economic Journal will publish “Impatience, Incentives, and Obesity” this month. Download the new NBER study at http://goo.gl/XU8NdV and “Impatience, Incentives, and Obesity” at http://onlinelibrary.wiley.com/doi/10.1111/ecoj.12124/abstract.