Changes in body composition of adult obese (ob/ob) and lean mice fed restricted levels of diets high in carbohydrate, fat or protein.

Adult obese (ob/ob) and lean male mice were fed severely-restricted amounts (approximately 20 to 30 per cent of ad-libitum intake) of either a high-carbohydrate, high-fat or high-protein diet for three weeks. All mice were fed an equal amount of metabolizable energy. Total body fat, total body nitrogen and skeletal-muscle nitrogen were measured in separate groups of mice initially and following three weeks of energy restriction. Obese mice lost 38 to 75 per cent more body energy than did lean mice. Fat accounted for most of the total energy lost (80 to 95 per cent). Obese mice lost more fat, but less protein, than lean mice. Of the total body protein lost by lean mice, 40 to 50 per cent was from skeletal muscle; but obese mice lost very little skeletal-muscle protein. Composition of the diet fed did not significantly affect losses of body weight, fat or protein in either obese or lean mice; mice fed the high-protein diet had heavier livers and kidneys. These results suggest that adult obese mice expend more total energy than lean mice. In addition, loss of body protein during restricted energy intake may be more closely related to remaining body fat stores than to composition of the diet.