Caloric Restriction and Protein Metabolism in the Growing Mouse

The effects of restricting the caloric intake by decreasing the consumption of fat and carbohydrate while holding constant the protein, vitamin, and mineral intakes have been studied in growing mice. Under such conditions there were observed: (1) a decrease in growth rate; (2) a decrease in the efficiency of protein and calorie utilization for growth; and (3) a decrease in energy expenditure. Extra quantities of dietary protein caused increased growth to approximately the same extent in mice receiving an adequate caloric intake or a caloric intake restricted to about one-half the adequate level. With low caloric intakes, extra calories in the form of protein caused a much greater growth response than equivalent calories supplied as fat or carbohydrate. Under the conditions of this study, in which all diets contained some fat, carbohydrate, and protein, fat and carbohydrate were equal in their protein-sparing effect.