Beyond BMI - Phenotyping the Obesities

For more than a decade, researchers in the field of obesity have debated the value of the BMI as the most common and convenient index for classifying the obese condition. The implications of using BMI are profound. The cut-off points of BMI of <18.5 kg/m 2 , 18.5–24.9 kg/m 2 , 25.0–29.9 kg/m 2 , 30.0–34.9 kg/m 2 , 35.0–39.9 kg/m 2 and 40.0+ kg/m 2 define categories usually referred to as underweight, normal weight, overweight (pre-obese) and obese (grades I, II and III). These cut-off points therefore define the number of individuals falling into each category which, in turn, tells us the prevalence of obesity on the planet. However, the essence of obesity is adipose tissue in the body (not a relationship of height and weight), so the BMI can only serve as an indirect estimate of obesity. Obesity is defined as an excess accumulation of body fat, and this excess fat is normally conceived as an indicator of poor health and, in turn, constitutes a risk factor for a range of diseases including diabetes, ischaemic heart disease, hyperlipidaemia, sleep apnoea, arthritis and others [1] . The BMI is therefore a measure of the number of people in the world who are in poor health, and who possess a condition that is threatening to their longevity or their quality of life. This has implications for who should be concerned (about themselves) and who should be a candidate for treatment (by others). Since the risk of early death or a life of disease prompts actions by public health authorities or medical agencies, the economic consequences are profound. If BMI provides a faulty quantification of who is at risk, then the personal, social and economic consequences are serious. However, BMI is an anthropometric concept and therefore serves only as a surrogate measure for fatness. Although BMI correlates with percentage body fat, the correlation between both parameters is not sufficiently accurate to truthfully reflect the amount of fat in Received: June 25, 2014 Accepted: July 14, 2014 Published online: October 23, 2014