If you’re one of the millions of Americans who struggle with obesity, part of the problem may lie in where you grocery shop. A new study found people who frequent lower-cost supermarkets tend to be heavier than those who shop at pricier stores.

Researchers from the University of Washington in Seattle analyzed data culled from local residents, taking into account their demographics, education and income — and what they found was rather startling.

Almost a third of people who shopped at stores with the lowest prices were obese, while only 9 percent who went to higher-priced stores were severely overweight. In addition, only one in seven participants said they shopped at the nearest supermarket — which may bust some previous theories that said easy proximity to healthier stores would have an effect on obesity rates.

In other words, heavier people tend to shop where it’s cheapest, and those stores seem to have fewer healthy choices than more expensive retailers (think Whole Foods, for example).

“Systematic efforts to reduce obesity will need to take economic inequalities into account,” the study’s authors wrote in a news release. “Ensuring equitable access to healthy, affordable foods — with the emphasis on affordable — may be key.”