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Why giving people easy access to a supermarket doesn't improve their health

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In recent years, there's been a lot of attention paid to food deserts, those culinary wastelands without supermarkets.

The conventional wisdom is that food deserts are a major public health problem and a potential driver of obesity: If people don't have access to fresh and healthy foods, they'll turn to fast food and other processed junk. So, the argument goes, eliminating food deserts would be a major boon. To that end, the US government has spent more than $500 million building supermarkets in food deserts since 2011.

Others, however, argue that this focus on food deserts may be misplaced and unproductive. There's nothing wrong with building a supermarket per se. But obesity and other public health problems are knotty and can't be solved so simply.

Jason Block, a physician and researcher at Harvard Medical School, recently published an analysis of the science of food deserts in the journal PLOS. He's argued, among other things, that building a supermarket in a food desert hardly has any effect on health. What seems to be far more important is changing behavior and helping people make better decisions no matter where they shop. I talked to him more about his research.

Julia Belluz: There's a big policy focus on food deserts — yet you point out that fewer than 1 percent of the population lives in a food desert. Isn't this lower than government estimates?

Jason Block: The USDA's definition of a food desert is very precise. Food deserts are defined at the census tract level, and to be a food desert requires two components: that a census tract is low income, and that people living in the census tract have limited access to a supermarket or large grocery store. That's 23.5 million people, which is approximately 7 percent of the population.

But you could also look at a different measure — those who live in food desert and don't have access to a privately owned car. That's 2.3 million people, or 1 percent.

Julia Belluz: So why are food deserts such a disproportionate object of focus?

Jason Block: There’s been this conventional wisdom for a long time that the food you have easy access to dictates the food you consume or purchase. This makes sense at first glance because it seems we're likely to shop in places that are convenient, and if we don't have access to healthy food options in our neighborhood, eating healthfully is going to be more of a challenge.

I think that’s a nice idea in theory. But I think the evidence really doesn’t bear that out.

Julia Belluz: So what happens when you build a supermarket in a food desert?

Jason Block: Several older studies have shown how resourceful people are. Even when they live in a food desert, people typically shop at a supermarket or a large grocery store. More recently, several quasi-experimental studies have looked at the introduction of a new supermarket into a food desert. Those studies tracked diet measures, body mass index, and perceptions of food access [of nearby residents] before and after the new supermarket opens.

What those studies have found is that perception of food access improves after the introduction of new supermarket — but diet doesn't improve that much, and body mass index doesn't change. It would be hard to move the needle on body mass index with the introduction of a supermarket, but the lack of improvement in dietary quality is disappointing.

Julia Belluz: Does that imply that food deserts themselves don't have a huge impact on health and obesity?

Jason Block: That's my read. Supermarkets might provide economic support to communities, and this is a worthy reason to promote them. But they don't seem to improve health. Another study looked at the fast-food ban in southern Los Angeles. That study was even less impressive — there was no effect on fast-food consumption or body mass index.

Julia Belluz: This jibes with the research you've done on menu labeling, which suggests that it's hard to change people's behaviors.

Jason Block: There are some corollaries with this research. The subjects in the calorie-labeling studies do report seeing and using calorie labeling more often — it just doesn’t seem to impact their decisions. [Similarly,] in these neighborhoods with new supermarkets, people do report access to healthy foods after these supermarkets are open, but it doesn't seem to impact their diet at all.

Julia Belluz: So if not food desert policies, then what?

Jason Block: One thing we're trying to highlight here is that there have been a lot of policy efforts on behalf of putting new supermarkets in food deserts. What there's been a lot less of a focus on is helping people to make better decisions once they actually get inside stores.

Supermarkets have become a combination of fast food and healthy food. So if you build a new supermarket in a neighborhood, it may give people better access to healthier foods —but it also might give them a higher amount of access to junk foods.

There are a number of things that can be done inside stores to help improve the dietary quality of purchases. Policymakers, public health professionals, and others should work with retail companies to help guide people to healthier choices. One way is to provide dietitian guidance in stores or to organize stores to better promote healthier items.

Food assistance programs are important too. If you provide subsidies for fruits and vegetables, this might impact how many people purchase those things. And, we could tax the unhealthiest items, like sugary drinks.

Julia Belluz: Seems like food deserts are yet another example of how simplistically we think about food and obesity.

Jason Block: It’s shorthand for how simplistically we think about all health policies. Health is incredibly complex. Obesity is a good example of this. For a public health problem that’s so significant today, we need to be doing as much as we can, focusing on those strategies that are likely to be most effective.