Influence of Low, Intermediate and High Levels of Dietary Protein on Heat Production of Rats

Abstract

An experiment was performed in which 28 young, growing male albino rats were fed diets based upon casein, glucose monohydrate and lard plus corn oil as the protein, carbohydrate and fat sources, respectively. The 4 diets, essentially isocaloric and containing approximately 8, 25, 41 and 57% protein, were fed in equal quantities within each of 7 quadruplicates of animals for a 53-day period with total collection of excreta. Carcasses of experimental animals, diets and excreta were analyzed for nitrogen and energy. Weight gain, feed efficiency and the N, energy and dry matter of the weight gain were at maximal values at the 25% level of dietary protein. The N of feces and urine increased with increasing percentage of dietary protein. Digested energy tended to remain constant, but metabolized energy decreased with increasing percentage of dietary protein above 25% protein. The specific dynamic effect of the food and the total heat production (gross energy of food minus the sum of energy of excreta and energy of the weight gain) of the animals decreased as the dietary protein increased from 8 to 25% and then increased as the dietary protein increased from 25 to 57%. The compatibility of these results with the general principle that the optimal overall utilization of a diet will occur when all required nutrients are at optimal levels was pointed out. The applicability of the general observations to the interpretation of results of similar studies involving human subjects was suggested.