This time of year, thoughts turn from overloaded holiday tables to overweight bodies, the beach, and diet programs. Losing weight is not just a matter of looking good in a swimsuit. Packing on the pounds increases a person's risk of heart disease, diabetes, high blood pressure, stroke, and some cancers. Recent surveys estimate that more than 50 percent of adults in the United States are overweight. As the U.S. public has gotten fatter, public health officials have been pushing diets low in fat. A variety of epidemiological data supports this advice, but it's now being challenged as other types of weight-loss diets have gained support.