The Big PictureA)It is lunch time at Eastside Elementary School in Clinton, Mississippi, the fattest state in the fattest country in the Western world. Uniformed lunch ladies stand at the ready. Nine-year-olds line up dutifully, trays in hand. Yes to chocolate milk, yes to fried chicken sandwiches, yes to orange jelly, no to salad. Bowls of lettuce and tomatoes sit side to side, rejected. Regina Ducksworth, in charge of Clinton’s lunch menu, sighs. "Broccoli(西兰花)is very popular," she says, reassuringly.B) Persuading children to eat vegetables is hardly a new struggle, nor would it seem to rank high on the list of global priorities. In an age of plenty, individuals have the luxury of eating what they like. Yet America is now worrying about how its citizens eat and how much exercise they take. It has become an issue of national concern.C) Two-thirds of American adults are overweight. This is defined as having a body mass index (BMI, a common measure of obesity) of 25 or more, which for a man standing 175cm tall means a weight of 77kg or more. Alarmingly, 36% of adults and 17% of children are not just overweight but obese, with a BMI of at least 30, meaning they weigh 92kg or more at the same height. If current trends continue, by 2030 nearly half of American adults could be obese. Americans may be shocked by these numbers, but for the rest of the world they fit a stereotype. Hamburgers, sodas and ice-creams are considered as American as the Stars and Stripes.D) The rest of the world should not scoff at Americans, because belts in many other places are stretched too, as shown by new data from Majid Ezzati of Imperial College, London, and Gretchen Stevens of the World Health Organisation (WHO). Some continental Europeans remain relatively slender. Swiss women are the slimmest, and most French women don’t get fat, as they like to brag (though nearly 15% do). But in Britain 25% of all women are obese, with men following close behind at 24%.E) And it is not just the rich world that is too big for its own good. The world’s two main hubs for obesity are the Pacific islands and the Gulf region. Mexican adults are as fat as their northernneighbours. In Brazil the tall and slender are being replaced by the pudgy, with 53% of adults overweight in 2008. Even in China, one adult in four is overweight or obese, with higher rates among city-dwellers. In all, according to Dr Ezzati, in 2008 about 1.5 billion adults, or roughly one-third of the world’s adult population, were overweight or obese. Obesity rates were nearly double those in 1980.F) Not long ago the world’s main worry was that people had too little to eat. Malnourishment remains a serious concern in some regions; some 16% of the world’s children, mainly in sub-Saharan Africa and South Asia, were underweight in 2010. But 20 years earlier the figure was 24%. In a study of 36 developing countries, based on data from 1992 to 2000, Barry Popkin of the University of North Carolina found that most of them had more overweight than underweight women.G) The clearest explanation of this extraordinary modern phenomenon comes from a doctor who lived in the 5th century BC. "As a general rule," Hippocrates wrote, "the constitutions and the habits of a people follow the nature of the land where they live." Men and women of all ages and many cultures did not choose gluttony and laziness over moderation and hard work in the space of just a few decades. Rather, their surroundings changed dramatically, and with them their behaviour. Much of the shift is due to economic growth. BMI rises in line with GDP up to $ 5,000 per person per year, then the correlation ends. Greater wealth means that bicycles are abandoned for motorbikes and cars, arid work in the fields is exchanged for sitting at a desk. In rich countries the share of the population that gets insufficient exercise is more than twice as high as in poor ones.H) Very importantly, argues Boyd Swinburn of Deakin University in Melbourne, diets change. Families can afford to eat more food of all kinds, and particularly those high in fat and sugar. Mothers spend more time at work and less time cooking. Food companies push their products harder. Richard Wrangham of Harvard University says that heavily processed food may have helped increase obesity rates. Softer foods take less energy to break down and finely milled grains can be digested more completely, so the body absorbs more calories. I) These global changes react with local factors to create different problems in different regions. In some countries malnutrition is leading to higher obesity rates. Undernourished mothers produce babies who tend to gain weight easily, which makes children in fast-developing countries particularly prone to getting fat. In Mexico unreliable tap water and canny marketing have helped make the country the world’s leading consumer of Coca-Cola; the average adult consumed 728 servings last year. In America junk-food calories are often cheaper than healthy ones. Suburban sprawl and the universal availability of food have made the car the new dining room. In the Middle East, Bedouin traditions of hosting and feasting have combined with wealth to make overeating a nightly habit. Any inclination to exercise is discouraged by heat and cultural restrictions. J) Together, these dissimilar changes have caused more and more people to become fat. Many cultures used to view a large girth with approval, as a sign of prosperity. But obesity has costs. It lowers workers’ productivity and in the longer term raises the risk of myriad illnesses, including heart disease, strokes and some cancers; it also affects mental health. In America, obesity-related illness accounted for one-fifth of total health-care spending in 2005, according to one paper. K) A huge new global health study, led by Christopher Murray of the University of Washington, shows that since 1990 obesity has grown faster than any other cause of disease. For women a high BMI is now the third-largest driver of illness. At the same time childhood mortality has dropped and the average age of the world’s population has risen rapidly. In combination these trends may mark a shift in public-health priorities. Increasingly, early death is less of a worry than decades spent alive and sick. L) It is plain that obesity has become a huge problem, that the factors influencing it are hard to untangle and that reversing it will involve difficult choices. Radical moves such as banning junk food would go against individuals’ freedom to eat what they like. Instead, some governments are cautiously spurring their citizens to eat less and exercise more, and food companies are offering at least some healthier foods. M) In a few places obesity rates seem to be leveling, but for now waistlines in most countries continue to widen. Jiang He and his colleagues at Tulane University have estimated that by 2030 the global number of overweight and obese people may double to 3.3 billion. That would have huge implications for individuals, governments, employers, food companies and makers of pharmaceuticals (药品).The third-largest cause of illness for female is a high BMI.