The epidemiology of obesity has for many years been diﬃcult to study because many countries had their own speciﬁc criteria for the classiﬁcation of diﬀerent degrees overweight. Gradually during the 1990s, however, the body mass index (BMI) (weight/height2) became a universally accepted measure of the degree of overweight and now identical cutoﬀ points are recommended. This most recent classiﬁcation of overweight in adults by the World Health Organization is the following (1):
In many community studies in aﬄuent societies, this scheme has been simpliﬁed and cutoﬀ points of 25 and 30 kg/m2 are used for descriptive purposes. Both the prevalence of very low BMI (<18.5 kg/m2) and very high BMI (40 kg/m2 or higher) are usually low, in the order of 1-2% or less. Already researchers in Asian countries have criticized these cut points. The absolute health risk (particularly of type 2 diabetes mellitus) seems to be higher at any level of the body mass index in Chinese and South Asian people, which is probably also true for Asians living elsewhere. There are some suggestions to lower the cut points to designate obesity or overweight by several units of body mass index (e.g., 23 kg/m2 for overweight and 25 kg/m2 for obesity) in Asian populations. In countries such as China and India, each with over a billion inhabitants, small changes in the criteria for overweight or obesity potentially increase the world estimate of the number of obese people by several hundredmillion (current estimates are f250 million worldwide).