About two-thirds of the adult U.S. population is overweight.¹ Almost one-third not only exceeds ideal weight, but also meets the clinical criteria for obesity. In the 1990s, rates of obesity more than doubled, and are currently rising by over 5% per year.^{2, 3} Excess body weight is implicated as a risk factor for many different disorders, including heart disease, diabetes, several cancers (such as breast cancer in postmenopausal women, and cancers of the uterus, colon, and kidney), prostate enlargement (BPH), female infertility, uterine fibroids, and gallstones, as well as several disorders of pregnancy, including gestational diabetes, preeclampsia, and gestational hypertension.⁴ The location of excess body fat may affect the amount of health risk associated with overweight. Increased abdominal fat, which can be estimated by waist size, may be especially hazardous to long-term health.^{5, 6}

For overweight women, weight loss can significantly improve physical health. A four-year study of over 40,000 women found that weight loss in overweight women was associated with improved physical function and vitality as well as decreased bodily pain.⁷ The risk of death from all causes, cardiovascular disease, cancer, or other diseases increases in overweight men and women in all age groups.⁸ Losing weight and keeping it off is, unfortunately, very difficult for most people.^{9, 10} However, repeated weight loss followed by weight regain may be unhealthy, as it has been associated with increased heart disease risk factors and bone loss in some studies.^{11, 12} Rather than focusing on weight loss as the most important health outcome of a change in diet or lifestyle, some doctors advocate paying more attention to overall fitness and reduction in known risk factors for heart disease and other health hazards.¹³

Excess body mass has the one advantage of increasing bone mass—a protection against osteoporosis. Probably because of this, researchers have been able to show that people who successfully lose weight have greater loss of bone compared with those who do not lose weight.¹⁴ People who lose weight should, therefore, pay more attention to preventing osteoporosis.