Desertification in action

ON WEDNESDAYS, Saturdays and Sundays in Santa Monica, a wealthy ocean-front city next to Los Angeles, residents toting canvas bags stock up on organic kale, locally caught seafood and exotic grains at farmers’ markets. If they cannot find the type of carrot or kumquat they are after among the tented stands, they can round out their shopping at the half-dozen grocery stores within a few miles of them.

Fifteen miles away in South Los Angeles, an impoverished area, the pickings are far slimmer. On Manchester Boulevard, one of the neighbourhood’s main corridors, there are many liquor stores, a Domino’s Pizza and a chicken joint called “Wingstop” that accepts food stamps, but few grocery stores. In the past residents have complained that those supermarkets that do exist truck in rotten food from wealthier neighbourhoods. (The supermarkets deny this.)

This disparity in the availability of wholesome food is often cited to explain why the wealthy eat more healthily than the poor. Santa Monica drowns in crisp vegetables, South Los Angeles in crisp bags. It is only logical that residents of the former would eat more fibre and less sugar than residents of the latter. Similar dynamics play out far beyond southern California. Low-income bits of the country are more likely to be “food deserts”, defined by the United States Department of Agriculture as places where one-third of the population lives at least one mile away from the closest supermarket in urban areas and at least ten miles away in rural areas.

But a study by Hunt Allcott of NYU, Rebecca Diamond of Stanford, and Jean-Pierre Dubé of Chicago Booth suggests the disparity in how the rich and poor buy groceries is caused more by demand than supply. Supply gaps are real and glaring, the study concedes. More than half (55%) of ZIP codes with a median income under $25,000 have no supermarkets, compared with 24% of ZIP codes across America as a whole. But, the researchers showed, introducing low-income populations to the same grocery shopping conditions enjoyed by high-income ones reduces nutritional inequality by only 9%. The remaining 91% of the nutritional gap, the academics contend, can be accounted for by differences in demand.

To reach this conclusion, the authors looked at two things. Using data about grocery purchases from 60,000 households and sales at 35,000 stores between 2004 and 2015, they first analysed what happens when new supermarkets open in poor areas. Then they looked at how poor households’ grocery shopping habits change when they move into neighbourhoods with healthier options. In both cases, they found little impact on the nutritional value of grocery purchases.

This raises an obvious question: what about plain old cost? The study finds that there is little price difference for categories other than fresh produce. Excluding fresh fruits and vegetables, the economists calculate that healthy foods such as plain yogurt and high-grain bread are actually 8% less expensive than unhealthy foods. The researchers conclude that preference, which is partly informed by education and nutritional knowledge, is a much more significant factor in how people decide what to buy at the grocery store. Changing that will be hard and will take time. Other research suggests the gap between the diets of rich and poor Americans is widening along with income inequality.