IN HIS book “In Defence of Food: An Eater’s Manifesto”, Michael Pollan urged people to “Eat food. Not too much. Mostly plants.” Although a paltry 2.7% of Americans have a “healthy lifestyle”, according to the Mayo Clinic, their diets are improving. A recent study by researchers at the Tufts University Friedman School of Nutrition Science and Policy, tracking changes in eating habits between 1999 and 2012, suggests that Americans are nibbling more whole fruits, nuts and seeds, and gulping fewer sugary drinks, than they were in the fairly recent past. But the study also revealed that the gap between the diets of rich and poor seems to be widening.

That rich Americans eat more healthily than poor ones is not a new revelation. Low-income places are less likely to have full-service grocery stores or farmers’ markets, let alone organic stuff. Poor people often have no cars, so they have to shop at the sort of convenience stores that offer crisps and doughnuts rather than fresh produce. And fruit and vegetables are heavy to lug home. In Newark, New Jersey, Renée Fuller, an elderly woman who walks with a stick, has to go to the next town, West Orange, to shop. “You want a banana, you have to travel. There’s not many supermarkets. There’s nothing convenient…You have bodegas and corner stores that sell cold cuts and sandwiches, but not many vegetables…I get my food stamps once a month. I can’t stock up on fruits for the whole month.” Low-income urban areas that are at least a mile from the nearest supermarket, and rural areas that are at least ten miles from any grocery store, are considered “food deserts”. In 2009 the Department of Agriculture calculated that 11.5m people, or 4.1% of America’s population, live in such deserts.

If fresh food becomes more available, though, it will not necessarily get eaten. In Morrisania, a deprived neighbourhood in New York’s unhealthiest county (and, until recently, a food desert), the launch of a supermarket did not markedly change eating habits. Kelly Brownell, the dean of the Sanford School of Public Policy at Duke University, says that makes sense: “Supermarkets offer more choice of healthy foods, but also ice creams and salty snacks.” In a survey conducted in 2012, over half of Americans claimed ignorance: working out their income tax, they said, was easier than knowing how to eat healthily. Employees at City Seed, a food-based charity based in New Haven, Connecticut, agree that availability is only part of the puzzle. By hosting farmers’ markets that accept Supplemental Nutrition Assistance Programme benefits, formerly known as food stamps, the group’s founders wanted to improve access to fresh foods where it “was easy enough to find pizza, but next to impossible to locate a fresh tomato”. Nicole Berube, the executive director of City Seed, not only hopes to bring healthy food closer, but also to build on the skills of people who know how to choose it and cook it—skills that exist even in deprived places.

Rising income inequality may also help to explain why American diets are becoming less equal. Adam Drewnowski, a professor of epidemiology at the University of Washington’s School of Public Health, estimates that the difference between eating healthily and poorly in America is $1.50 a day. For a family of five, that is over $2,700 a year. Dariush Mozaffarian, a doctor and one of the authors of the eating-habits study, thinks time constraints are even more important. “Low-income individuals might have to work two jobs to support their families, or make long commutes. Such commitments might get in the way of cooking healthy meals.”

Dr Mozaffarian believes it is crucial to change cultural attitudes towards nutrition. The tobacco industry offers a useful example. As smoking has become less socially acceptable, smoking rates have declined. If people could come to view inhaling cheesecake or Big Macs in the same way, Americans’ waistlines would shrink along with their health-care bills.

Over one-third of American adults are not just overweight, but obese. Past research suggests obesity and the preventable chronic diseases that go with it cost the country between $147 billion and $210 billion a year. Dr Mozaffarian believes the economic toll is even higher, and yet nutrition is not tracked in most electronic health records. “This should be a top national priority,” he says; “up there with terrorism.”