The macronutrient composition of the diet can influence hunger, satiety, food intake, body weight, and body composition. Fat, not carbohydrate, is the macronutrient associated with overeating and obesity. Fat is overeaten because it is highly palatable and because it provides a high level of energy in a given volume of food. However, when given in equal volumes, carbohydrate (sugar) and fat have similar effects on hunger, satiety, and subsequent food intake when infused intragastrically or ingested in foods by normal-weight, unrestrained young men. In obese and restrained subjects, preloads of high-carbohydrate yogurts suppress subsequent food intake more than do high-fat yogurts, indicating a relative insensitivity to the satiety value of fat. Both the amount of fat in the diet and total energy intake should be managed in weight-loss regimens. Low-fat foods and fat substitutes can help to reduce fat intake. Although more data are required, currently the best dietary advice for weight maintenance and for controlling hunger is to consume a low-fat, high-carbohydrate diet with a high fiber content.