Illustration by KAL

A FEW years ago, Burger King, a fast-food chain, conducted a study of the eating habits of some of its most frequent customers. A few dozen “SuperFans”, as the firm calls them, recorded and photographed everything they ate for two weeks. The results were collected in a book called “Food for Thought”. Unsurprisingly, this book is not publicly available: amateur photos of heaps of junk food are hardly an enticing advertisement for a firm that supplies the stuff. Nonetheless, “Food for Thought” gives an insight into why some Americans have such poor diets.

The fast-food fans in the book typically lead chaotic lives. They often toil long, irregular hours for not much money. They grab food when they can, skipping many meals and gorging at unorthodox times. They favour whatever is quick, convenient and comforting. (“I selected the pie because it was easy to grab out of the fridge,” says one.) They often have an imperfect grasp of nutritional science. (“I am eating chocolate muffins at work because they are not too heavy,” says another.) Oddly for a piece of corporate research, the book contains passages that are quite moving. One single dad's diary shows him eating nothing but junk for days on end. Then, one evening, he visits his aunt's house and she cooks him a feast of real food: pork, okra stew, collard greens and corn bread.

At 33.8%, America's obesity rate is ten times higher than Japan's. In all, 68% of Americans are either obese or overweight. (Some studies yield lower numbers, but since they typically ask people how much they weigh, rather than weighing them, scepticism is in order.) Few problems, besides death, afflict more people. Americans are more likely to be overweight than to pay federal income tax.

But the good news is that the nation may have stopped getting fatter. A study published this month in the Journal of the American Medical Association (JAMA) found that American women were no more likely to be obese in 2008 than they were nearly a decade before. For men, there was a small rise in obesity over the same period, but no change in the past three years. Among children, too, there was no change in obesity rates except among the very heaviest boys, whose numbers increased slightly. Could it be that the American obesity epidemic has reached a plateau?

If the national girth really has stopped expanding, that would be a blessing, though of course it is a big fall in obesity that is really required. Although a little extra heft is no big deal, many Americans are so ample that it ruins their health. That places a burden on the health-care system: each obese American racks up medical bills 42% higher than an American of normal weight, according to Eric Finkelstein and Justin Trogdon, writing in Health Affairs. Add to that the indirect costs of obesity, such as lost productivity due to sickness or premature death.

The startling Republican victory in Massachusetts this week throws Barack Obama's health reforms up in the air. But the issue will not go away. And a plateau in the obesity rate would make some kind of reform a bit less expensive. It will not lead to a sudden dip in health-care costs, predicts Mr Trogdon. But it could substantially slow the rate at which they are rising. Previous projections typically assumed that Americans would keep on ballooning. As a thought experiment in 2008, Youfa Wang of the Johns Hopkins Centre for Global Health drew a line from recent trends and projected that 100% of Americans would be overweight by 2048. By 2030, his model showed health-care costs attributable to excess weight approaching a trillion dollars a year.

The latest numbers remind us how little is known about public health. Of course, people put on weight when they consume more calories than they burn off. But no one knows for sure why America's obesity has trebled since 1960. Plausible theories abound. As people grow richer, food becomes relatively cheaper. Time grows more precious: hence the lure of fast food. Desk work burns fewer calories than spadework. And labour-saving devices do just that: if we still washed dishes and clothes by hand, we would burn off five pounds of flesh each year, reckons Barry Popkin, the author of a book called “The World is Fat”. All this is no doubt true, but it does not explain why Americans are fatter than people in other rich countries, nor why they appear to have stopped getting fatter.

No to nannies

Kathleen Sebelius, the health secretary, says that “fighting obesity is at the heart” of health reform. But telling people to eat more healthily is like telling them not to have risky sex. Americans are suspicious of the nanny state at the best of times, let alone when it nags them to curb their most basic instincts. Some regulations help: forcing restaurants to post calorie counts on dishes, for example, prompts diners to pick less calorific treats. But politicians are reluctant to attack voters' favourite vices too vigorously. A recent proposal to tax sugary drinks, for example, went nowhere. Opponents argued that it would disproportionately affect the poor. True enough, but the poor are disproportionately likely to be overweight.

The constant barrage of pro-vegetable propaganda in schools may have raised awareness of the need for a balanced diet, reckons Mr Trogdon. And popular pressure has prompted many fast-food outlets to offer salads and other wholesome fare. But even if good food were freely available, losing weight is hard. Every year, 25% of American men and 43% of American women attempt it. “[F]ailure rates are exceedingly high,” notes a JAMA editorial. But there is hope. Eating is social. Studies suggest that people guzzle more if they have overweight friends and relatives, and less if they don't. So if Americans have stopped getting fatter, their children have a better shot at staying trim.





Economist.com/blogs/lexington