No developed nation tips the scales quite like the United States, where 68 per cent of the adult population is overweight, according to a report released last month by the Organisation for Economic Co-operation and Development (OECD). Yet obesity rates have been growing globally at an alarming rate in the past 30 years, creating public health concerns in many wealthy countries. With 22.5 per cent of its population overweight and 7.1 per cent obese, China ranks among the slimmest OECD nations, along with Japan and South Korea. But the mainland's rapid economic development and urbanisation are fuelling an obesity problem that could spiral out of control. 'China is, in a sense, a very large and very fast-moving test case of what's happening in developing countries as they become more affluent,' says researcher Matthew Crabbe, co-author of the book Fat China: How Expanding Waistlines are Changing a Nation. The mainland's obesity rate may seem relatively low, but it has doubled every decade since the 1980s. 'It's obvious that a significant problem has developed quickly in just 20years,' Crabbe says. The OECD statistics are too broad to reflect a true picture of the emerging crisis; the extent of obesity in the cities is obscured because the figure is offset by a large rural population, which has far fewer people with weight problems. 'It's one country, but two eating systems,' says Mylene Khoo, director of Tetra Nutritional Consultation Centre and a dietitian who has treated more than 20,000 people with obesity. 'Half of China is still a developing country. Cities like Shanghai or Beijing are moving towards a more urbanised, Westernised lifestyle, [while] in rural areas, access to and variety of food are still limited.' Unlike the US, where obesity is seen as a working-class problem, it is largely an issue for affluent and educated urban Chinese. Higher incomes, accessibility to a wider variety of foodstuffs and the emergence of the middle-class consumer have all changed the way people eat. Eating is central to how Chinese people socialise and do business; there is strong social pressure to eat out more, drink more alcohol and consume more convenience foods. Whereas huge banquets used to be reserved for special occasions such as weddings, even minor events are now cause for celebration. The mainland's one-child policy has had an effect on childhood obesity, too, with parents and grandparents lavishing attention and earnings on the only child. The Six-Pocket Syndrome, as Crabbe and co-author Paul French call it, is aggravated by the Chinese perception of chubbiness in children as a sign of good health. 'It is completely fu [fortunate] to have a fat child,' Khoo says. 'So the urban state of mind [is] to encourage your child to be roly-poly.' Parents who grew up in less prosperous times may enjoy plying their children with treats such as ice cream and McDonald's Happy Meals. Some observers attribute China's bulging waistlines to a growing prevalence of fast-food outlets, such as KFC, McDonald's and local equivalents. 'Western fast food and products have increasingly become a part of the Chinese diet,' Crabbe says. 'But the Chinese foods that people are eating have become more Westernised in terms of delivery and production - more processing and use of sugary and high-fat sauces, in supermarkets, retail and catering. In competition with Western fast food, they are using stronger flavourings, sugar, salt and MSG [monosodium glutamate, a flavour enhancer] because they've got to have that taste hit to get people hooked.' Despite the pressure to eat out and eat more, the lifestyle in Chinese cities - characterised by long office hours, irregular meals and too little sleep - can result in less sociable eating patterns dictated by convenience and time, which goes against Chinese tradition. The stress of a modern lifestyle can cause a considerable slowdown of the metabolism and trigger overeating through snacking, Khoo says. Experts are having a tough time reaching a consensus on the magnitude of the mainland's weight problem. 'The science and the numbers are all very vague,' Crabbe says. 'There seems to be some dispute among those in the medical profession on how you define obesity - particularly within different racial groups, lifestyles and body types, that simple measures like the Body Mass Index [BMI] don't seem to quite grasp.' The World Health Organisation uses the BMI, a ratio comparing body weight to height, where people falling within a BMI range of 25 to 29.99 are considered overweight, and a BMI of 30 or higher is classed as obese. Studies have shown that, owing to differences in body fat distribution, a large proportion of Asian people within the WHO's normal BMI range are still at high risk for type-2 diabetes, heart disease and other metabolic disorders. For governments, an increasingly obese population poses economic problems in terms of treatment costs and also loss of productivity, paid sick leave, disability and premature death. The WHO published a series of reports in 2008 on reform of the health system on the mainland, documenting the emergence of chronic non-communicable diseases, such as diabetes, coronary heart disease, hypertension and others. The prevalence of chronic disease is expected to grow, along with the economic costs. For direct obesity-related problems alone, the authors of Fat China estimate the likely cost was roughly US$155 billion in 2005, based on the most recent obesity rates and an assumed per capita cost of treatment. Using a similar broad-stroke method of calculation, they project the cost in 2020 to be roughly 29.2 per cent of total health care spending. '[The mainland health system] is not equipped to handle these costs,' Crabbe says. 'Although a lot of money has been pumped into the health care system, much of it is going [on] setting up the basic health care system in rural areas; urban consumers are being left with their own bill for their health problems.'