The Plane of Intake of Beef Muscle Protein as Affecting the Energy and the Nitrogen Metabolism of the Mature Albino Rat

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Abstract
The effects of the plane of protein intake on the utilization of the food protein and energy of equicaloric diets containing 10%, 25% and 45% of protein, respectively, were investigated in a 70-day balance experiment with mature albino rats as subjects. The rats remained in approximate equilibrium with respect to live weight and to the nitrogen content of their bodies. The digestibility of the protein of the diets increased in the order of the increase in dietary protein; and the digested nitrogen and the urinary nitrogen were essentially the same values. The metabolizable energy diminished in the order of the increasing protein contents of the diets, primarily because the increase in the outgo of urinary energy more than counterbalanced the coincident decrease in feces energy, from the two higher protein as compared with the lowest protein diet. The heat production diminished, slightly, in the order of the increase in protein in the diets, this diminishing heat production being equivalent to a slightly increasing heat in relation to the metabolizable energy. Urinary nitrogen per calorie of urinary energy increased in the same order as the increase in dietary protein. The bearing of the results in relation to human diet is pointed out.