Public HealthAppropriate body-mass index for Asian populations and its implications for policy and intervention strategies
Introduction
WHO has recommended classifications of bodyweight that include degrees of underweight and gradations of excess weight or overweight that are associated with increased risk of some non-communicable diseases.1, 2 These classifications are based on body-mass index (BMI), calculated as weight in kilograms divided by height in metres squared (kg/m2). As a measure of relative weight, BMI is easy to obtain. It is an acceptable proxy for thinness and fatness, and has been directly related to health risks and death rates in many populations.
In 1993, a WHO expert committee meeting1 proposed BMI cut-off points of 25·0–29·9 kg/m2 for overweight grade 1, 30·0–39·9 kg/m2 for overweight grade 2, and “$$”40·0 kg/m2 for overweight grade 3. In 1997, a WHO expert consultation2 proposed an additional subdivision at a BMI of 35·0–39·9 kg/m2, recognising that management options for dealing with obesity differ above a BMI of 35kg/m2.
The 1993 expert committee emphasised that weight gain in adult life is associated with increased morbidity and mortality at increasing BMIs, and that cut-off points for the amount of overweight should not be interpreted in isolation but in combination with other risk factors of morbidity and mortality. Type 2 diabetes, cardiovascular disease and increased mortality are the most important sequelae of obesity and abdominal fatness, but other associations are seen in musculoskeletal disorders, limitations of respiratory function, and reduced physical functioning and quality of life.3
The WHO BMI classifications of overweight and obesity are intended for international use. They reflect risk for type 2 diabetes and cardiovascular diseases, which are rapidly becoming major causes of death in adults in all populations—even in those who still have substantial malnutrition. However, the absolute prevalence and incidence of type 2 diabetes varies greatly among ethnic groups, such as the very high prevalence in Pima Indians, and including some who have simliar BMIs, such as higher rates in Taiwanese and Japanese Americans than in European populations.3
Three specific factors led WHO to convene another expert consultation on BMI classifications. First, there was increasing evidence of the emerging high prevalence of type 2 diabetes and increased cardiovascular risk factors in parts of Asia where the average BMI is below the cut-off point of 25 kg/m2 that defines overweight in the current WHO classification. Second, there was increasing evidence that the associations between BMI, percentage of body fat, and body fat distribution differ across populations. In particular, in some Asian populations a specific BMI reflects a higher percentage of body fat than in white or European populations. Some Pacific populations also have a lower percentage of body fat at a given BMI than do white or European populations. Third, there had been two previous attempts to interpret the WHO BMI cut-offs in Asian and Pacific populations,4, 5 which contributed to the growing debates on whether there are possible needs for developing different BMI cut-off points for different ethnic groups.
The WHO expert consultation on BMI in Asian populations, which met in Singapore from July 8–11, 2002, focused exclusively on issues related to overweight and obesity. The consultation therefore did not discuss the health consequences at the low range of BMI (ie, <18·5 kg/m2), which indicates underweight, though this has been addressed before.1 Here, we discuss the highlights of the expert consultation's deliberations, describe the evidence base available for review, and present the main conclusions and recommendations of the consultation.
Section snippets
Asian populations
The umbrella term Asian characterises a vast and diverse portion of the world's population. Diversity in Asian countries is based on ethnic and cultural subgroups, degrees of urbanisation, social and economic conditions, and nutrition transitions. There are also many Asian immigrants throughout the world to whom the considerations addressed in the consultation might apply. When taken together, these populations cover a wide range of morbidity and mortality profiles, social and economic
BMI and body fat
A series of analyses of BMI, body composition, and risk factors in Asian populations was compiled for the consultation from studies in China, Hong Kong, India, Indonesia, Japan, Republic of Korea, Malaysia, Philippines, Singapore, Taiwan, and Thailand.25 Of the 15 data sets initially analysed to assess the relation between BMI and the percentage of body fat in Asians, six sets were later excluded because the method used for assessment of body composition (bioelectrical impedance or
Conclusions
On the basis of the available data in Asia, the WHO expert consultation concluded that Asians generally have a higher percentage of body fat than white people of the same age, sex, and BMI. Also, the proportion of Asian people with risk factors for type 2 diabetes and cardiovascular disease is substantial even below the existing WHO BMI cut-off point of 25 kg/m2. Thus, current WHO cut-off points do not provide an adequate basis for taking action on risks related to overweight and obesity in
Research needs
The consultation did not have enough data to adequately describe either the association of BMI with body fat, or the association of BMI or fatness with morbidity and mortality in populations in Asian countries, or in subgroups within countries. Furthermore, some of the available data were not suitable for cross-population comparisons because of the techniques used to assess body fat. Some data from earlier attempts to address Asian BMI issues were just being published.5
Meaningful body
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