Clinical Definition of Overweight and Obesity

Obesity is a disease characterized by excess adiposity that is a source of extensive morbidity and mortality due to various weight-related complications. Therefore, the diagnostic evaluation should consist of an anthropometric measure that reflects increased fat mass and an indication of the degree to which the excess adiposity is adversely affecting the health of individual patients. Body mass index (BMI) is widely used as the anthropometric measure in the screening and diagnosis of overweight (BMI 25–29.9 kg/m2) and obesity (BMI ≥ 30 kg/m2), and in the classification of obesity severity (BMI class I = 30–34.9 kg/m2, class II = 35–39.9 kg/m2; and class III = ≥40 kg/m2). However, BMI inter-relates height and weight and is not a direct measure of adiposity since, in addition to fat mass, weight is comprised of lean mass, bone, and extracellular fluid volume. Thus, BMI is an appropriate screening tool but must be interpreted in the context of a physical examination that confirms excess adiposity in making the diagnoses of overweight or obesity. Moreover, the BMI is not a reliable indicator of the impact of excess adiposity on health, which can vary extensively among patients at any given level of BMI. The component of the diagnostic evaluation that assesses health involves a careful clinical assessment of the risk, presence, and severity of weight-related complications. The two-component approach, involving both anthropometric and clinical evaluation, provides a meaningful and actionable diagnostic framework that helps guide clinical decisions regarding the aggressiveness of therapy.