About one fifth of the one billion overweight or obese people in the world are Chinese. China was once considered to have one of the leanest populations,1 but it is fast catching up with the West in terms of the prevalence of overweight and obesity; disturbingly, this transition has occurred in a remarkably short time.2
Data from the 2002 national nutrition and health survey showed that 14.7% of Chinese were overweight (body mass index (BMI; kg/m2) ≥ 25) and another 2.6% were obese (BMI ≥ 30), such that there are currently (2002) 184 million overweight people, and a further 31 million obese people, in China, out of a total population of 1.3 billion (table).3 Although the prevalence of obesity in China is relatively low compared with Western countries such as the United States, where over half of adults are either overweight or obese, it is the rapid increase of the condition,4 especially among children, that is particularly alarming. Data from the China national surveys on the constitution and health in school children showed that the prevalence of overweight and obesity in children aged 7-18 years increased 28 times and obesity increased four times between 1985 and 2000 (figure),5 a trend that was particularly marked in boys.
Increasing evidence indicates that the World Health Organization's definitions of overweight (BMI > 25) and obesity (BMI > 30) may underestimate the true burden of the condition. These cut points are derived from white populations and hence may not be applicable to Asians. On the basis of a meta-analysis of associations of BMI with risk factors for cardiovascular disease among 240 000 Chinese adults, and of the longitudinal relationships of BMI to cardiovascular events in 76 000 participants, the Working Group on Obesity in China has recommended that a BMI of 18.5 to 23.9 should be considered as optimal, 24.0 to 27.9 as overweight, and 28.0 and above as obese.6,7 These recommendations have been used in the guidelines for prevention and control of overweight and obesity in Chinese adults.8 Using these cut points rather than the WHO definitions would increase the prevalence of overweight and obesity in China by a further 66 million, to over a quarter of a billion people (table). More informative measures of obesity, such as waist circumference or waist:hip ratio, are considered to be more strongly correlated with cardiovascular risk and may be more appropriate for use in Asian populations, in whom central adiposity has been shown to occur at lower levels of BMI than in white people.
The explanations of China's recent epidemic of overweight and obesity include changes to the traditional diet, reduced levels of physical activity, and increased sedentary lifestyles. Recent data from the national surveys of nutrition indicate noticeable changes in the proportions, and sources, of dietary macronutrients over the past 20 years. Energy intake from animal sources has increased from 8% in 1982 to 25% in 2002,3 and the average energy intake from dietary fat among urban Chinese increased from 25% to 35%,9 which is above the upper limit of 30% recommended by the WHO. The obesity epidemic in China may also have its roots in the prevailing social attitudes towards body fatness. In Chinese culture, there is still a widespread belief that excess body fat represents health and prosperity. This is perhaps a consequence of China's recent history, where famine and chronic malnutrition caused the deaths of millions of people in the 1950s.
Coinciding with China's continuing modernisation are reductions in physical activity and labour intensity in both urban and rural areas. People are expending less energy on traditional forms of transportation such as walking and cycling, and the popularity of cars, buses, and motorcycles is increasing. Data from the national statistics bureau show that the number of cars produced in China quadrupled from 5400 in 1980 to over 2 million in 2003—almost all of which are sold in China. Furthermore, the lack of consideration towards constructing environments in inner cities that promote physical activity has meant that it has become increasingly difficult to find safe places in residential areas to exercise or even walk.
As in other countries, China's epidemic of overweight and obesity poses a considerable public health problem, and it is becoming increasingly clear that we need to act now to prevent any further increase. The means by which this may be accomplished remain elusive. In randomised trials, intensive lifestyle education has been shown to result in modest but sustained weight loss; the feasibility and efficacy of conducting such studies in China is uncertain but should be investigated. As a first step, the prevention and control of obesity should be listed in China's framework and policy on health. By confronting the challenge now, China may be able to halt the growing problem of overweight and obesity, doing what the West has so far failed to do.