Americans consume many more calories than needed, and the excess is leading to diabetes, cardiovascular disease, and premature mortality. Since the 1970s, caloric intake has increased by some 200 to 600 calories per person per day.1 Although it is unclear how important changes in physical activity are to the surge in obesity prevalence, it is quite clear that this increase in calorie consumption is the major cause of the obesity epidemic—an epidemic that each year is responsible for the deaths of more than 100 000 Americans2 and accounts for nearly $150 billion in health care costs.3