In addition to BMI, another factor that has been found to be helpful in predicting obesity related risk for developing health problems is waist circumference.
Obesity is the result of a complex interaction between genetics and environment.
It is true that some people are able to eat more than others without gaining weight. However, it is clear that people of all genetic backgrounds can effect changes in their weight and body shape by increasing their physical activity and decreasing the amount of fat and energy in their diets. Although most obese people do not have an obvious, treatable underlying medical problem it is important to have a medical evaluation prior to beginning a weight loss program. Some medical causes of weight gain that should be screened for include hypothyroidism, endocrine tumors, polycystic ovaries and Cushing's disease. Also some medications can cause weight gain and might be eliminated or substituted when possible.