Many have argued that those who live in unhealthy food environments — heavy on fast food, light on grocery stores — are more likely to consume less nutritious options. But Roland Sturm, an economist at RAND Corporation, analyzed the food environments of 13,000 adolescents in California, looking at how many fast-food restaurants and supermarkets were within a 1.5-mile radius of their homes and schools. He then looked at how much fast food, fresh fruits and other foods the kids consumed. And his study found no correlation between what food sources kids lived near, what the kids ate and how much they weighed.

“The idea of a supermarket desert is something everyone is really interested in,” says Sturm, whose research focuses on the intersection of urban design and health care status. “The big concern I have right now is there is policy being guided by some spurious findings.”

Why doesn’t living near a supermarket correlate with better nutrition? Sturm thinks a lot of the explanation has to do with transportation and how people get to the grocery store. “Maybe the whole idea that what is 400 meters away is no longer relevant when people drive everywhere. In California, we see about 97 percent have access to motorized transportation. Where they get their food could have little to do with what’s directly in their neighborhood.”

The other key issue has to do with what fast-food restaurants and supermarkets sell. Grocery stores do sell fruits and vegetables. They also sell candy and chips. “That makes the storyline a little more complicated than a supermarket will make you think,” Sturm notes. “By the same logic, supermarkets also make you drink soda.”

Sturm doesn’t disagree with the idea that supermarkets can benefit a neighborhood: They provide more food variety and more options for eating healthily. But he cautions against turning to a supermarket expansion as a way to address American obesity.

“I think it’s an important data point,” he says,”And I think we should look at what, exactly, the associations are between food environment and obesity. It’s not a hot, sexy paper. But it’s an important piece of the story.”