The simplest and most widely recognised definition of obesity is in terms of BMI. A detailed description of BMI measurements is given in the assessment section.

Essentially, the higher the BMI the greater the risk of morbidity and mortality. The health risks associated with obesity are widely recognised. There is a strong link between obesity and the risk of cardiovascular disease (CVD).^3–6 Additional evidence suggests that a substantial number of cases of type 2 diabetes could be avoided if individuals were to stay within a healthy weight range. For example, the risk of type 2 diabetes is 80-fold greater in an individual with morbid obesity (BMI >40 kg/m2), compared with an individual with a BMI <22 kg/m^{2_. 7} Several prospective studies have demonstrated the relationship between obesity and premature death from coronary heart disease, cancers and other diseases. ^8–10