Demography of obesity

Introduction According to the World Health Organization (WHO), overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health [1]. Overweight and obesity are usually diagnosed when weight normalized for height, or body mass index (BMI: weight in kilograms divided by the square of the height in meters, kg/m2), exceeds a defined threshold. In 1995, the WHO proposed a BMI classification for adults as a form of diagnosing excess adiposity [2]. According to this classification, individuals are considered overweight when their BMI is ≥25; those between 25 and 29.9 are designated as pre-obese and they are classified as obese when their BMI reaches or exceeds 30 kg/m2 (Table 1.1). Many authors also use the term “overweight” to designate pre-obese individuals (BMI 25–29.9), which gives rise to some confusion, unless the specific range of BMI is specified. Although BMI does not directly measure the percentage of body fat, it offers a more accurate assessment of excess adiposity than weight alone. Due to its simplicity, BMI categorization is the preferred obesity measurement for clinicians, public health specialists, and researchers, and is currently used worldwide to track adult overweight and obesity prevalence [3]. Although BMI categorization is widely used, it has several limitations. The proposed BMI classification is age and gender independent and it may not reflect the same degree of adiposity in different populations, due to different body proportions in different ethnicities. Therefore, since the health risks associated with increasing BMI are continuous, the interpretation of BMI gradings in relation to risk may differ for different populations. Due to a growing debate in recent years on the need to develop different BMI cut-off points for different ethnic groups, the WHO convened an expert consultation on BMI in Asian populations [4] to address this issue. Despite evidence that Asian individuals may be at higher than average risk at BMIs lower than the existing WHO cut-off point for overweight (25 kg/m2), the experts observed that there is a large heterogeneity among the ideal cut-off points for