The Utilization of Energy Producing Nutriment and Protein as Affected by the Plane of Protein Intake

Abstract

Corresponding to progressively greater protein contents of equicaloric diets, from 10 to 45%, were increased digestibility and decreased metabolizability of food energy; decrease in heat production at a diminishing rate of decrease; increase in energy of urine; increase in gain in body weight and in energy of body gain until the optimum proportion of protein in the diet was reached, and, with further increase in protein, slight decreases in rate of gain in weight, energy, nitrogen and fat, and in fat gained per gram of nitrogen gained. The nutritive balance of the diets as sources of energy was obviously improved, corresponding to their progressively greater protein contents from 10% to 25%, as evidenced by marked increase in energy of body gain; and approximately equal decrease in heat production—the metabolized energy remaining virtually unchanged. Corresponding to further increase in the protein contents of the diets from 25 to 45%, the nutritive balances of the diets as sources of energy were slightly impaired, as evidenced by appreciable decrease in the quantity of energy utilized for body gain, due to more rapid decrease in metabolizable energy than in heat production—the decrease in metabolizable energy resulting from an increase in energy of urine which exceeded the slight decrease in energy of feces. Corresponding to progressively greater protein contents of the diets from 10 to 45%, there was a slight decrease in the proportion of food nitrogen appearing in the feces; a considerable increase in the proportion appearing in the urine; and first a marked increase, followed by a marked decrease, in the proportion utilized for body gain. The plane of protein intake did not materially affect the basal energy metabolism. The results tend to sustain the idea that the specific dynamic effects of protein, carbohydrate and fat, as their relative values are ordinarily understood, do not apply in relation to the mixed diets of nutritive practice; and the idea that neither individual nutrients nor individual feeding stuffs express their maximum, normal, nutritive values except as components of complete diets.