Lower BMI cut-off value to define obesity in Hong Kong Chinese: an analysis based on body fat assessment by bioelectrical impedance

There is increasing evidence suggesting that the cut-off values for definin g obesity used in the Western countries cannot be readily applied to Asians , who often have smaller body frames than Caucasians. We examined the BMI a nd body fat (BF) as measured by bioelectrical impedance in 5153 Hong Kong C hinese subjects. We aimed to assess the optimal BMI reflecting obesity as d efined by abnormal BF in Hong Kong Chinese. Receiver operating characterist ic curve (ROC) analysis was used to assess the optimal BMI predicting BF at different levels. The mean age and sd of the 5153 subjects (3734 women and 1419 men) was 51.5 (SD 16.3) years (range: 18.0-89.5 years, median: 50.7 y ears). Age-adjusted partial correlation (r) between BMI and BF in women and men were 0.899 (P < 0.001) and 0.818 (P < 0.001) respectively. Using ROC a nalysis, the BMI corresponding to the conventional upper limit of normal BF was 22.5-23.1 kg/m(2), and the BMI corresponding to the 90 percentiles of BF was 25.4-26.1 kg/m(2). Despite similar body fat contents, the BMI cut-of f value used to define obesity in Hong Kong Chinese should be lower as comp ared to Caucasians. We suggest a BMI of 23 kg/m(2) and 26 kg/m(2) as the cu t-off values to define overweight and obesity respectively in Hong Kong Chi nese.