A NEW website from the US Department of Agriculture (USDA) shows that 10% of the country is now a “food desert”. The Food Desert Locator is an online map highlighting thousands of areas where, the USDA says, low-income families have little or no access to healthy fresh food. First identified in Scotland in the 1990s, food deserts have come to epitomise urban decay. They suggest images of endless fast-food restaurants and convenience stores serving fatty, sugary junk food to overweight customers who have never tasted a Brussels sprout.

The USDA links food deserts to a growing weight problem that has seen childhood obesity in America triple since 1980 and the annual cost of treating obesity swell to nearly $150 billion. Accordingly, Michelle Obama announced a $400m Healthy Food Financing Initiative last year with the aim of eliminating food deserts nationwide by 2017.

Official figures for the number of people living in food deserts already show a decline, from 23.5m in 2009 to 13.5m at the launch of the website in May. Although this might on the face of it suggest that the initiative is off to a superb start, sadly it does not in fact represent a single additional banana bought or soda shunned. This is because in America, the definition of a food desert is any census area where at least 20% of inhabitants are below the poverty line and 33% live more than a mile from a supermarket. By simply extending the cut-off in rural areas to ten miles, the USDA managed to rescue 10m people from desert life.

Some academics would go further, calling the appearance of many food deserts nothing but a mirage—and not the real problem. Research by the Centre for Public Health Nutrition at the University of Washington found that only 15% of people shopped for food within their own census area. Critics also note that focusing on supermarkets means that the USDA ignores tens of thousands of larger and smaller retailers, farmers’ markets and roadside greengrocers, many of which are excellent sources of fresh food. Together, they account for more than half of the country’s trillion-dollar retail food market.

A visit to Renton, a depressed suburb of Seattle, demonstrates the problem. The town sits smack in the middle of a USDA food desert stretching miles in every direction. Yet it is home to a roadside stand serving organic fruit and vegetables, a health-food shop packed with nutritious grains and a superstore that University of Washington researchers found attracts flocks of shoppers from well outside the desert.

No surprise, then, that neither USDA nor the Institute of Medicine of the National Academies has been able to establish a causal link between food deserts and dietary health. In fact, both agree that merely improving access to healthy food does not change consumer behaviour. Open a full-service supermarket in a food desert and shoppers tend to buy the same artery-clogging junk food as before—they just pay less for it. The unpalatable truth seems to be that some Americans simply do not care to eat a balanced diet, while others, increasingly, cannot afford to. Over the last four years, the price of the healthiest foods has increased at around twice the rate of energy-dense junk food. That is the whole problem, in an organic nutshell.