Adult obese rats were restricted to equal intakes provided by four diets which varied widely in protein, fat and carbohydrate content. Loss in body weight and body fat was similar in all groups. The only significant dietary effect observed was a modest increase in the body protein content of the animals fed the high protein diets. Low carbohydrate--high fat--high protein diets, as expected, showed no advantage as reducing diets when compared to other diets on an equal calorie basis.