The objective was to study the relationship between body mass index (BMI) and body fat per cent (BF%) in different population groups of Asians. The study design was a literature overview with special attention to recent Asian data. Specific information is provided on Indonesians (Malays and Chinese ancestry), Singaporean Chinese, Malays and Indians, and Hong Kong Chinese. The BMI was calculated from weight and height and the BF% was determined by deuterium oxide dilution, a chemical-for-compartment model, or dual-energy X-ray absorptiometry. All Asian populations studied had a higher BF% at a lower BMI compared to Caucasians. Generally, for the same BMI their BF% was 3-5% points higher compared to Caucasians. For the same BF% their BMI was 3-4 units lower compared to Caucasians. The high BF% at low BMI can be partly explained by differences in body build, i.e. differences in trunk-to-leg-length ratio and differences in slenderness. Differences in muscularity may also contribute to the different BF%/BMI relationship. Hence, the relationship between BF% and BMI is ethnic-specific. For comparisons of obesity prevalence between ethnic groups, universal BMI cut-off points are not appropriate.

Three different adult Indonesian population groups living on Sumatra (Palembang), Java (Depok) and Sulawesi (Makale) participated in a study on body composition. Body weight, body height and multifrequency bioelectrical impedance (1, 5, 50 and 100 kHz) were measured and in addition total body water (TBW) and extracellular water (ECW) were determined by dilution techniques, using deuterium oxide and sodium bromide, respectively, as tracers. In total 318 subjects, 159 males and 159 females, participated in the study. Predicting ECW and TBW from bio-electrical impedance, using existing prediction formulas from the literature, did not result in valid estimates of these parameters. Therefore new prediction equations for ECW and TBW were developed in this group and the prediction equations were validated in several subgroups. Extracellular water (kg) could be predicted with the formula 0.262 height2/Z1 + 2.7 (SEE = 0.9 kg) and TBW with the formula 0.516 height2/Z100 + 3.5 (SEE = 1.6 kg), where Z1 and Z100 are impedances at frequency 1 and 100 kHz, and SEE is the standard error of estimate. The prediction formulas showed good validity in the three geographical subgroups, in males and females separately and in two randomly selected subgroups. The absolute prediction error (kg) of the newly developed prediction equations is lower compared with values normally reported in the literature, but when expressed as coefficient of variation the errors are comparable with values from the literature. Addition of weight age and sex (for TBW only) improves the prediction equation. The prediction equations were compared with prediction equations developed in Dutch subjects. In the Indonesian subjects the slopes of the regression equations were not different from the Dutch equations but the intercepts were lower. This means that for the same body water compartment and for the same height Indonesians have lower impedance values. This could be explained by a slightly higher ECW/TBW ratio and a more slender body build among Indonesians. A higher environmental temperature and skin temperature of the subjects in this study could have added to the effect. The formulas should preferably be validated before applying them to other Asian populations.