Study: Warehouse clubs are making us fatter

What makes Americans obese? We can point pudgy fingers at giant restaurant portions or weigh the effect of sedentary Netflix binges, but here’s another hefty culprit: supercenters and warehouse clubs like Costco, Sam’s Club, BJ’s Wholesale, and Walmart. Georgia State University health economist Charles Courtemanche looked at dozens of economic factors that might have contributed to the rise in U.S. obesity and concluded that, without a doubt, restaurants and big-box stores have had the biggest impact. We asked him to elaborate on his findings, which were published in a working paper by the National Bureau of Economic Research.

The connection between restaurants and obesity seems obvious. What made you look at big-box stores? That goes back to a paper I published in 2011 documenting the link between Walmart Supercenters and obesity rates. We had known from other studies that Walmart and warehouse clubs led to significant reductions in food prices, and we knew that food prices were associated with body weight. This new paper is more a synthesis of what I and others have been working on for the last decade. We put all these factors in a statistical horse race to see which survive and which don’t.

What were considerations in that horse race? We’re not talking about, “We gain weight because we’re eating more or exercising less.” As economists, we’re interested in why we eat more or exercise less. We wanted to know: Is it cheap food? Is it more readily available food? Is it the movement of people into the suburbs? Into sedentary jobs?

What results surprised you? Obesity researchers in general would’ve expected more impact from sedentary jobs, but very little showed up to indicate that being in a very active job made a difference. The timing of the shift from blue-collar to white-collar jobs predates rising obesity.

Is the impact that we buy—and thus eat—in bulk? It could be either low prices or buying in bulk. If I had to guess, it would be prices, because you see the same impact at Walmart as at warehouse clubs.

You don’t need a PhD for this story. It could be as simple as that food’s cheaper so people eat more of it, it could be bulk, or it could be a grander story that shopping is switching from walking around downtown to driving out to the suburbs. It could be a complicated combination of all these things. Or it could be simply: “These stores sell really cheap food, and that makes people gain weight.”

Do the stores affect all shoppers? The effects are concentrated among people already at risk for being obese or those over the threshold for being overweight. The stores are harmless for most, but for some people, they trigger self-control issues.

How do restaurants factor in? It seems it’s a time/cost rather than a money/cost connection. If there are no restaurants within walking distance of your office, you bring your lunch. But if there are 20 restaurants, you eat out three times a week. On average, restaurant food is less healthy than food you prepare.

So, what should we do? Economists think more about policy than what individuals should be doing. This isn’t saying avoid Costco. There are great benefits to shopping there; you can save a ton of money. I think it’s more like: If you know you’re going to shop there, realize there are going to be temptations.