The need for appropriate BMI cut-off values to define obesity among Asians. (Editorial).
The use of the Quetelet's index or body mass index (BMI, kg/[m.sup.2]) to compare the physique of man was first advocated as far back as in the nineteenth century (1). This index has been found to be the most suitable compared to other weight-height indices as it is minimally correlated with height while being highly correlated with body fat percentage (2,3). In a 1997 consultation, WHO recommended that the BMI cut-off values for overweight and obesity to be 25 kg/[m.sup.2] and 30 kg/[m.sup.2] respectively (4). These recommendations were based on the presence of excessive body fat and adverse effects on health (mortality and morbidity). However studies supporting these cutoff points were those conducted among Caucasian populations.
Indications that the relationship between BMI and body fat percentage differs across population groups surfaced in 1994 with the publication of Norgan (5). This was followed by the work of Wang et al. (6), showing that Asians living in New York have lower BMI but higher body fat percentage compared to age-matched Caucasians. Recently, studies in Indonesia, Singapore, Japan and Hong Kong demonstrated that for the same BMI, Asians living in these countries have higher body fat percentage compared to age- and sex-matched Caucasians with the same BMI (7-10). Reasonable comparisons among these studies are hampered by the varying methods used to assess or estimate body fat percentage and use of non-standardised techniques and non-validated methodologies. Ideally a chemical model using a maximum of body compartments should be employed for cross population comparisons but it is not feasible for many countries. Deuterium oxide dilution might be the most feasible alternative, as it is found to be valid (11,12), the met hod is easy to standardise, application is relatively easy even in field situations and samples can be sent for analyses to a specialised laboratory.
More importantly, the populations in many Asian countries such as Singapore, Hong Kong, China, Japan, Korea, Thailand, India and Malaysia (13-20) are also experiencing elevated cardiovascular risk factors (both absolute and relative risks) at levels of BMI considered to be normal by WHO. Various levels of BMI cut-off points for obesity were proposed in these populations, ranging from BMI of 25 kg/[m.sup.2] to 28 kg/[m.sup.2] for the different populations. Some countries, such as Indonesia and Japan, have proceeded to revise their BMI cut-off points for obesity based on their own findings.
Recognising the need to address this pressing issue to define obesity among Asians, WHO convened an expert consultation in July 2002, where Asian and international experts deliberated whether population-specific BMI cut-off points for overweight and obesity are necessary. Data from various Asian countries (China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, Philippines, Singapore, Thailand and Taiwan) were analysed and discussed during the consultation. It was acknowledged that Asians generally have higher body fat percentage compared to Caucasians and experience elevated risks at lower levels of BMI. The expert consultation emphasised that risk is a continuum along the BMI scale, and cut-offs merely act as triggers for action at various risk levels. It recommended BMI cut-off points of 23 kg/[m.sup.2] (moderate to high risk) and 27.5 kg/[m.sup.2] (high to very high risk) for Asians instead of 25 kg/[m.sup.2] and 30 kg/[m.sup.2] for Caucasians respectively.
The implications of this recommendation are apparent. The prevalences of overweight and obesity would be much higher than official figures. For example, in Singapore alone, the proportion of adults in the overweight category would increase from 24% to 35% while obesity prevalence would be 14% instead of 6%. If this were also true for other Asian countries, it would mean that almost half of the adult population in Asia would be at risk for obesity-related illnesses. This would form an escalating public health problem that cannot be ignored, as predicted by the WHO expert consultation group back in 1997 (4). Commitment, resources and concerted actions would be required at all levels, from national to individual levels to address the risk factors for obesity, chiefly the imbalance between energy intake and expenditure. Strategies and measures need to be instituted for different settings such as schools and workplaces, besides the general community, to reduce the prevalences of obesity and its comorbidities, part icularly among high-risk groups in each country.
Policy makers and program planners would need to be extra vigilant in designing health promotion programs to accompany the changes in BMI cut-off points. It is pertinent to craft public education messages that the priority and focus should not be in losing weight, but rather losing excessive body fat and maintaining optimal BMI level through an active lifestyle and sensible diet that is appropriate for the level of physical activity. Doctors and health professionals need to be alerted that weight loss measures through medication and/or surgery are suitable only for the morbidly obese and not for the majority.
The review and revision of BMI cut-off points for Asians paves the way for future research and collaboration to develop indices of obesity that are appropriate for various population groups in Asia. More studies are needed to validate common anthropometric indices, e.g. waist circumference, waist to hip ratio, bioelectrical impedance analysis, skinfold thicknesses against reference methods to assess their suitability for use as surrogate measures of body composition in the field. These studies need to be accompanied by longitudinal studies for definitive quantification of the risks (morbidity and mortality) associated with these indices.
Health Promotion Board, Singapore
National University of Singapore
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