The ratio of body weight to squared stature, nowadays known as the body mass index (BMI), was proposed as an index of body shape in the late 19th century. BMI was rediscovered in the late 20th century as an index of body fat and started to be employed in population studies to investigate the association between body adiposity and disease. From these studies, BMI emerged as an important predictor of morbidity and mortality. However, BMI is not a pure index of adiposity because its numerator (body weight) is the sum of fat- and fat-free-tissues. Moreover, its association with disease is influenced by other factors such as age, gender, ethnic background, dietary habits and physical activity. Despite these limits, in our era of Evidence-based Medicine, the assessment of BMI is a central step in the evaluation and treatment of obesity, diabetes, hypertension and dyslipidemia and other complications of overweight.
