Several studies that have examined obesity say the proximity of neighborhoods to grocery stores is a factor in areas with higher rates of obesity, but a new study from researchers at the University of Washington thinks those studies got it wrong. Instead, they say it is access to healthy, affordable foods that is critical to tackling the obesity epidemic.

Most studies, the researchers say, have used distance to the nearest supermarket as the best predictor of whether people have good diets and better health. But Adam Drewnowski, UW professor of epidemiology and his team say that's not true. Their study found that six out of seven people shopped for food outside their immediate neighborhood. And while the closest supermarket for most people was less than a mile away, people chose the market that was more than three miles away. That’s because driving further to save money on groceries is common.

Physical proximity to a supermarket may not, by itself, assure a healthy diet, says Drewnowski, but “money does matter.”

Supermarket chains have specific demographics—consumers differ by age, education, income, health, and even obesity rates. The countywide obesity rate for King County, where Seattle is located, was 19.8 percent in 2007, but the obesity rate was only 4 percent among Whole Foods and PCC shoppers. “Consumers who shop at most area supermarket chains have obesity rates at 25 percent and higher,” says Drewnoski. “Clearly, not all supermarkets are the same and economic access is determined by price.”

“We plan to explore how local data can best be used in new initiatives to improve access to healthy, affordable foods in Seattle, King County, and throughout Washington State,” says Drewnowski. “We hope to provide the local answer to the question that the federal government is trying to address. And we want to make sure our public health initiatives and programs are backed by research and science.”