Obesity is defined as weight at least 20% above a person's "ideal": Twenty-40% over ideal weight is considered mildly obese, 40-100% over ideal weight is considered moderately obese, and more than 100% over ideal weight is severely (morbidly) obese. According to some estimates, about one fourth of the U.S. population can be considered obese, 4 million of whom are morbidly obese.

Excessive weight can result in many serious and potentially deadly health problems, including high blood pressure, diabetes, infertility and increased risk for heart disease and heart attack.

In common terms, "obese" means "very overweight" and often carries negative connotations. But in weight-control medicine, "obese" is a non-judgmental term that simply means a certain body mass index.

Body mass index (BMI) has been the medical standard for obesity measurement since the early 1980s, when government researchers developed it to take height into account in weight measurement. In BMI terms, the...