Living near a Walmart might be less convenient than you think. Why? Because the ubiquitous big box stores might be making America fat.
The finding is from a new study that analyzes a long list of economic factors–income, unemployment, urban sprawl, and two dozen more potential causes–to discover which were most strongly linked to Americans’ swelling waistlines. The number one factor, the authors found, was the expansion of supercenters and warehouse clubs.
Since the 1960s, as Walmart has sprawled across the U.S., adult obesity has jumped from 13% to 35%, and those facts seem to be related. The researchers, writing in a working paper published by the National Bureau of Economic Research, found that general economic factors can explain 37% of the rise in overall body mass index (BMI), and 59% of the rise in severe obesity. As they looked at each economic factor individually, big box stores had the most impact, along with growing numbers of restaurants.
Several other studies have looked at economic factors on America’s waistlines in the past, but usually one at a time. “The key is that the different economic factors are correlated with each other, so if you focus on just one at a time you are unlikely to get results that reflect causal effects,” says Charles Courtemanche, lead author of the paper and an assistant professor of economics at Georgia State University.
“To provide an example, an area with a lot of restaurants is also likely to have a lot of supercenters, warehouse clubs, general merchandisers, grocery stores, convenience stores, fitness centers, etc.,” he says. “So if you only study the effect of restaurants on obesity, you can’t be sure that you’re really picking up the causal effect of restaurants as opposed to just the effect of having more development and a stronger economy in general.”
Some of the changes that the researchers expected to matter, like the fact that many of us work at inactive desk jobs, actually didn’t make a difference. “The biggest reason these factors didn’t seem to explain much of the rise in obesity is simply because the trends don’t line up,” Courtemanche explains. “Most of the fall in on-the-job physical activity occurred in the mid-part of the 20th century, whereas the sharp rise in obesity didn’t start until the late 1970s. For a variable to contribute to the trend in obesity, it needs to be changing at the same time obesity is rising.”
While the researchers don’t know why stores like Walmart make populations fatter, they have some ideas.
“My best guess would be simply that they sell cheap food,” Courtemanche says. “There is good evidence that these stores have price advantages over competitors on the order of 10% to 30%, and there is also good evidence that cheaper food leads to weight gain. Another possibility is that the bulk buying at warehouse clubs leads people to have more food in the house, making it relatively easy to, for instance, grab that extra helping of potato chips.”
The study also had some good news: When fitness centers spread, or gas prices rise, people lose weight.