ABSTRACT
Obesity describes an increase in body fat to the level at which it has adverse effects on health. The degree of obesity is usually defined using the body mass index (BMI), calculated as weight (kg)/height (m2), and this is generally used in clinical practice and epidemiological studies (Table 39.1).1 Body mass index is only a surrogate measure of adiposity; studies using more accurate measures such as dual emission X-ray absorptiometry (DEXA) or magnetic resonance imaging show that there is a large variance in body fatness and of body fat distribution at any given level of BMI. Measurement of waist circumference or
waist/hip ratio may provide a better index of total body adiposity than BMI and therefore may better predict the risk of metabolic complications of obesity, such as diabetes and heart disease (Table 39.1).
