It’s a plausible hypothesis: Poor people in the United States suffer from measurably worse nutrition because they have such limited access to good food. Confronted with a high concentration of poor diet choices (fast food and processed food in convenience stores) and with few markets offering fresh fruit and vegetables, the poor end up eating a less healthy diet. In this view, bad diets are a problem with the urban environment—the lack of good food in poor neighborhoods.

But while there are certainly urban neighborhoods that lack good grocery options, is there any evidence that close physical access to food—as opposed to other factors like income or education—strongly determines healthy eating? That view deserves some skepticism.

A recent study by researchers at the University of Pennsylvania, Princeton, and the U.S. Department of Agriculture summarized in the Chicago Policy Review concludes that after controlling for differences in education and income, variations in physical access to food explain less than 10 percent of the variation in consumption of healthy foods. The researchers also find that the opening of new, healthier supermarkets in neighborhoods has very little effect on what nearby residents eat.

This new study reinforces earlier research that questioned whether the physical proximity to healthier eating choices is the root cause of poor nutrition and hunger.

Studies show that there is no apparent relationship between a store’s mix of products and its customer’s body-mass index. And limited experimental evidence suggests that improving the supply of fresh foods seems to have limited impacts on food-consumption patterns. Preliminary results of a study of consumers in a Philadelphia neighborhood that got better supermarket access didn’t find that they ate more fruits or vegetables, or lowered their body-mass index—including those who patronized the new store.

Physical proximity alone is not likely to be a strong explanation of variations in diet. Judged by proximity to grocery stores, nearly all of rural America is a food desert. Nathan Yau at FlowingData uses Google Maps data to construct a compelling map of how far it is to the nearest grocery store across the entire nation. The bleakest food deserts are the actual deserts of the American West, in Nevada and Wyoming.

City dwellers, particularly those in the biggest, most dense cities tend to live closest to supermarkets and have the best food access. WalkScore used its data and models to develop some clear images of who does (and doesn’t) have a good grocery store nearby. They estimate that 72 percent of New York City residents live within a five-minute walk of a grocery store. At the other end of the spectrum, only about 5 percent of residents of Indianapolis and Oklahoma City have that convenience. When it comes to walking, this data shows the real food deserts are in the suburbs.

There are other ways of measuring food access and mapping food deserts. The U.S. Department of Agriculture and PolicyMap have both worked to generate their own maps of the nation’s food deserts. They account for both neighborhood income levels and how far it is to the nearest grocery store.

While it’s clear that income plays a big role in food access, it’s far from clear how to combine income and proximity to define food deserts. The USDA uses an overlay to identify which low-income neighborhoods have limited food access. PolicyMap has a complicated process that compares how far low-income residents have to travel to stores compared to higher-income residents living in similarly dense neighborhoods.

But combining neighborhood income and physical proximity muddles the definition of food access. First, and most important, it acknowledges that income, not physical distance, is the big factor in nutrition. Both of these methods imply that having wealthy neighbors or living in the countryside means that physical access to food is not a barrier. Second, it is an individual’s household income, not her neighbor’s income, that determines whether she can buy food. Third, these methods implicitly treat low-income families differently depending on where they live. For example, PolicyMap excludes middle-income and higher-income neighborhoods from its definition of “limited supermarket access” areas—and therefore doesn’t count lower-income families living in these areas as having poor food access.

The fact that both of these systems use a different yardstick for measuring accessibility in rural areas suggests that proximity isn’t really the issue. Rural residents are considered by the USDA to have adequate food access if they live within 10 miles of a grocery store, whereas otherwise identical urban residents are considered to have adequate access only if they live within a mile or half-mile of a store.

When it comes to food access, the focus should be on poverty, not grocery store location. The argument here parallels that of the Nobel Prize-winning economist Amartya Sen, who pointed out that the cause of starvation and death in famines is seldom a physical lack of sufficient food, but is instead the collapse of the incomes of the poor. Sen’s conclusion was that governments should focus on raising incomes if they wanted to stave off hunger, rather than stockpiling or distributing nutritious food.

There are good reasons to believe that the built environment does play an important role in obesity. But, as a Surgeon General’s report implies, that role may have more to do with how easy it is to walk to all daily destinations, not just the fresh-food aisle. It’s tempting to blame poor nutrition and obesity on a lack of access to healthy choices, but poverty and poor education are much stronger predictors.


This post appears courtesy of City Observatory.