Shopping at lower cost supermarkets may be closely linked to higher obesity rates, reports a study published online yesterday in the American Journal of Public Health.

Researchers from the University of Washington sought to determine whether living near food stores or the food prices within the store would be more strongly associated with obesity rates.

Surveying residents of Seattle and King County, Wash., researchers collected and geocoded data on home addresses and food shopping destinations, including brand names and addresses of supermarkets that were identified as the primary food source. Supermarkets were stratified into three price levels based on the average cost of a market basket of 100 foods.

Researchers found that only one in seven respondents reported shopping at the nearest supermarket. They noted, “Although having a supermarket close by can shape shopping patterns in some urban locations, it may be less important in Seattle’s King County, where most people shop by car.”

In contrast, obesity rates were significantly different depending on the supermarket of choice. Obesity prevalence among shoppers in higher price supermarkets was 9 percent, which is less than half of the county average of 20.5 percent; whereas obesity prevalence among shoppers in lower price supermarkets was 27 percent, above the county average. Physical distance to the supermarket had no impact on obesity rates.

The main findings were that food costs trumped convenience. Bringing supermarkets closer to underserved areas may be one way to deal with the obesity epidemic. Reducing economic distance by making healthy foods more affordable is another strategy that should not be overlooked.

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