A major environmental risk factor for T2D is obesity, defined by > 120% ideal body weight or a body mass index (BMI) > 30 k/m2. Because obesity increases risk for T2D, the tremendous increase in the rates of T2D in recent years has been attributed, primarily, to the dramatic risk in obesity worldwide. It has been estimated that approximately 80% of all new T2D cases are due to obesity. This is true for children and adults.

In addition to general obesity, the distribution of body fat, estimated by the ratio of the waist-to-hip circumferences (WHR). WHR is a reflection of abdominal (central) obesity, which is more strongly associated with T2D than standard measures, such as BMI.