October 8, 2012

‘Food deserts’ abound in King County for those without cars, UW study shows

News and Information

King County has no substantial food deserts, provided one has a car.

Take away the car, however, and food deserts — areas where low-income people have limited access to low-cost, nutritious food — appear to fill the county map.

New research from the University of Washington, published in the American Journal of Public Health, shows only about one-third of the vulnerable populations studied could walk to a nearby supermarket, and as few as 3 percent could walk to a low-cost supermarket.

“Most of the research assumes that everybody has a car to go to and from the supermarket, which is not really true,” said Anne Vernez Moudon, professor of urban design and planning in the UW College of Built Environments, one of the paper’s authors.

“We have 5 to 8 percent of the population that doesn’t have a car. And if you take a family of four and you have one car, not everybody has access to the car all the time.”

map showing food deserts in king county relative to car ownership

Food deserts (black) and service areas (white) around low- and high-cost supermarkets in King County, defined as 10-minute walking and driving network distances. For those without access to a car, food deserts seem to fill the map.

Moudon said while previous research identifying food deserts used aggregated data from zip codes or census tracts, she and co-authors Philip M. Hurvitz, Adam Drewnowski and Jared Ulmer of the UW and Junfeng Jiao of Ball State University studied smaller, more specific census blocks instead, each the rough equivalent of an urban city block.

She said earlier studies also didn’t take into account food cost differences among supermarkets, assuming instead that the stores offer a similar variety of healthy foods at similar costs.

Moudon and co-authors say a better way to determine food deserts is to first evaluate a population’s access to supermarkets taking into account different modes of travel. Then measure economic access by dividing supermarkets into low-, medium- and high-cost, “with the assumption that low-income populations need to access low-cost supermarkets.”

The researchers identified five groups of low-income populations in King County to “test the effect of different measures of low income on the definition of food deserts.” For the first time in such a study, Moudon said, they factored in car ownership as a measure of population vulnerability. They also combined income and access criteria to estimate food deserts.

The five groups showed vulnerable populations — or those living in food deserts — ranging from 4 percent to 33 percent of the county’s population. Nearly all of the vulnerable populations they found in King County lived within a 10-minute drive or bus ride of a low- or medium-cost supermarket.

And on foot, at most 34 percent of the vulnerable populations could reach a supermarket at all, and only 3 percent could reach a low-cost store.

They found that while travel to a supermarket by public transit is possible, individual shopping needs don’t always coincide with transit routes or times. Having access to a car was the best guarantee for the majority of the vulnerable populations to reach any supermarket within 10 minutes, making food-shopping a car-dependent activity.

When supermarket access was defined as pedestrian access to a low-cost supermarket, the area defined as a food desert dramatically increased throughout the King County map.

Moudon said the results should be of interest to city planners and public health authorities seeking to reduce disparities in health. She said planners have historically left arranging access to healthy, low-cost food to developers and the private sector, but that trend is now changing. “The public health people are saying to the planners, ‘Don’t let people develop in areas unless you bring a food source,’” she said.

Moudon added, “So, the next time you read about [how there are no] food deserts in King County, you’ll say, ‘Yes, but let’s look at the map.’”

The research was funded by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases. Lead author Jiao earned his doctorate in urban design and planning from the UW.

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For more information or interviews, contact Moudon at moudon@u.washington.edu or 206-276-3133.