One way to learn more about factors that are associated with maintaining weight loss is to study the habits of individuals who have successfully lost weight and kept it off. Members of the National Weight Control Registry, an observational study of socalled successful losers, report consuming healthy, low-fat diets and engaging in high levels of physical activity. Obesity and overweight are common health problems, and their prevalence has increased dramatically in the past 30 years. Currently, half of all U.S. adults are overweight or obese (defined as a body mass index of 25 or more). Excess weight is associated with an increased risk for numerous health problems, including dyslipidemia, hypertension, cardiovascular disease, type 2 diabetes, and some cancers, and it has been estimated that up to 325,000 deaths per year in the United States are attributable to obesity.