Obesity in Hong Kong - Risk and Burden

Body Mass Index (BMI), defined as body weight in kilogram divided by body height in metre squared, has been used for measuring obesity for more than 20 years. The World Health Organization (WHO) in 1995 defined overweight as BMI 25-29.9 kg/m2 while obesity as BMI 30 kg/m2. However, these definitions are based on data obtained mainly from Caucasian populations and do not apply readily to Asian populations such as the Chinese. In 2000, the World Health Organization Western Pacific Region (WHO-WPR), International Association for the Study of Obesity (IASO) and the International Obesity Task Force (IOTF) jointly proposed a revised definition of obesity for non-Caucasian populations3. In this joint proposal, BMI cut-off levels for overweight and obesity in Asians were redefined as 23 kg/m 2 and 25 kg/m 2 respectively 3 . However, this modification had been criticised to be too radical such that the definition of obesity was dramatically decreased by 5 kg/m2 (from 30 to 25 kg/m2). In 2004, a WHO expert consultation was held in Singapore. They concluded that Asians generally had a higher percentage of body fat than white people of the same age, sex and BMI, and that the proportion of Asian people with risk factors for type 2 diabetes and cardiovascular diseases was substantial even below the existing WHO BMI cut-off point of 25 kg/m2 for overweight. They released a report that suggested retaining the traditional BMI cut-off levels for overweight ( 25 kg/m 2 ) and obesity ( 30 kg/m 2 ) but added 23.0, 27.5, 32.5 and 37.5 kg/m2 as points for public health action4. For Asian populations, BMI at 27.5 kg/m2 or higher was regarded as representing high risk4. Vague was the first to describe that obesity which predominates in the upper body is more associated with hypertension and glucose intolerance compared to obesity which predominates in the lower body5. To measure abdominal obesity, waist circumference (WC) alone and/or waist to hip ratio (WHR) are most commonly used. The measurement of WC should be made at the approximate midpoint between the lower margin of the last palpable rib and the top of the iliac crest6 while hip circumference is the maximum measurement, in a horizontal plane, around the buttocks posteriorly and the symphysis pubis anteriorly. Standardisation of the levels at which WC and hip circumferences should be measured is important since large variations in the ratio can result from small variations in the measurement sites. Some reports have shown that WC correlates better than WHR with intra-abdominal adipose area as measured by Computerised Tomography Scan or Magnetic