According to the U.S. Department of Agriculture (USDA), 23.5 million people in the United States live in food deserts—urban neighborhoods and rural towns without ready access to fresh, healthy, and affordable food. More than half of these individuals live in low-income households.

Americans who live in these areas may have no access to food at all, or only fast food or convenience stores with limited healthy options. The USDA says living in a food desert contributes to a poor diet and can lead to increased obesity levels and other diet-related diseases.

Policymakers have attempted to eliminate food deserts by increasing the availability of healthy foods. The federal government allocated $125 million to be spent annually in each of the next five years to bring healthy foods to underserved communities, and states have also introduced programs to improve access by providing loans, grants, and tax credits to stimulate supermarket development and to encourage retailers to offer healthy foods in food deserts.

Theoretically, providing individuals living in food deserts with healthier food options will cause them to eat healthier foods, but according to Jessie Handbury, an assistant professor of real estate at the Wharton School, that isn’t necessarily the case.

Handbury, also a faculty fellow at the Penn Institute for Urban Research, is the co-author of the working paper “What Drives Nutritional Disparities? Retail Access and Food Purchases Across the Socioeconomic Spectrum” with colleagues Molly Schnell of Princeton University and Ilya Rahkovsky of the USDA’s Economic Research Service.

Using six different datasets that collectively describe the nutritional quality of household food purchases, the stores located in the neighborhoods where these households reside, the nutritional quality of the products offered in these stores, and the demographics of these neighborhoods, the researchers found that even when controlling for access, disparities in healthy food consumption remain. Adding healthy food stores to food deserts produced little change in the eating habits of households, particularly among low-income and less educated households.

The paper does not resolve why the disparity continues to exist; Handbury says they plan to answer that question in future work.

“The big question that this analysis has brought for us is, ‘What else is going on?’” Handbury says. “Is it a budget constraint issue? Is it a price issue, that healthier foods cost more? Or is it a taste issue, and an issue of social norms?”

If the disparity stems from a price issue, Handbury says the government could change consumer purchase patterns by subsidizing healthy food products to make them less expensive, or by taxing unhealthy foods.

“If the reason that low-income households are eating unhealthy foods is because they’re cheaper, you make it so they’re not cheaper anymore,” she says, “either by making healthy foods cheaper, or by making unhealthy foods more expensive.”

If it is a taste issue—if people living in food deserts simply do not like the taste of healthy food—or a matter of social or cultural norms, Handbury says solving the problem is much more complex, and may require a broad education campaign about the pros of eating healthy foods and the cons of eating food that is not healthy.

“If it’s a taste issue and not a price issue, then by making unhealthy foods more expensive, you’re either disproportionately subsidizing the people who already like healthy foods, or you’re disproportionately taxing the people who like unhealthy foods without seeing much of a change in people’s behaviors,” she says. “It’s going to have this regressive effect, especially given the correlations along the income lines. You’re going to be essentially giving a subsidy to high-income households or taxing low-income households.”

Poor diets are often attributed to three factors: food deserts, preferences for unhealthy foods, and higher prices of healthy foods.

Handbury says part of the reason that public officials have zeroed in on access may be because they can see immediate results.

“You can say, ‘Look, here’s a store that entered in this neighborhood that didn’t have a store before,’” she says. “But, if the goal is for people to eat healthier foods, you may also need to take some steps to educate households on the benefits of the healthy foods available there.”

The researchers report that improving access to retail outlets alone will do little to close the gap in the nutritional quality of diets across different socioeconomic groups, and more than 90 percent of the disparities across education groups would persist.

“The conclusion is that we think there needs to potentially be a more integrated approach of trying to tackle multiple factors at the same time, not just focusing on food deserts as being the root cause,” Handbury says. “Because from what we’ve seen in this paper, they’re not.”