According to the National Institute of Health guidelines for the treatment of overweight and obesity, the most important element in a weight loss program is the reduction in energy intake. Reducing the fat content of the diet and increasing physical activity without restricting energy intake are relatively inefficient methods of weight loss. Because individuals tend to consume a constant weight of food, the decrease in energy intake on a reduced-fat diet is likely related to the lower energy density of the diet. Diets of low energy density, which are typically low in fat and rich in complex carbohydrates, allow individuals to consume satisfying portions of food while reducing their energy intake. Because a wide variety of foods can be included in a diet that is low in energy density, this type of diet encourages the adoption of life-long eating habits that are integral to the maintenance of weight loss and the prevention of weight gain.