More than 80 percent of cases of type 2 diabetes can be attributed to obesity.

1. There is a curvilinear relationship between BMI and the risk of type 2 diabetes.
2. Lowest risk is associated with a BMI below 22 kg/m2
3. At a BMI greater than 35 kg/m2, the relative risk for diabetes adjusted for age increases to 61. The risk may further increase by a sedentary lifestyle or decrease by exercise.
4. Weight gain after age 18 years in women and after age 20 years in men increases the risk of type 2 diabetes.
5. The Nurses’ Health Study compared women with stable weight (those who gained or lost <5 kg) after the age of 18 years to women who gained weight. Those who had gained 5.0 to 7.9 kg had a relative risk of diabetes of 1.9; this risk increased to 2.7 for women who gained 8.0 to 10.9 kg.
6. Similar findings were noted in men in the Health Professionals Study. The excess risk for diabetes with even modest weight gain is substantial.
7. Weight gain precedes the onset of diabetes. Among Pima Indians (a group with a particularly high incidence of type 2 diabetes), body weight gradually increased 30 kg (from 60 kg to 90 kg) in the years preceding the diagnosis of diabetes. Conversely, weight loss is associated with a decreased risk of type 2 diabetes.
8. Insulin resistance with high insulin levels is characteristic of obesity and is present before the onset of high blood sugar levels.
9. Obesity leads to impairment in glucose removal and increased insulin resistance, which result in hyperinsulinemia. Hyperinsulinemia contributes to high lipid levels and high blood pressure.