R. W. Swift

Fats in relation to caloric efficiency

SummaryThe efficiency of utilization of diets containing amounts of fat varying from 2 to 30% has been investigated in a series of metabolism studies using male albino rats as experimental subjects.All diets were compounded in a manner to make them equicaloric and to contain the same amounts of protein, vitamins, and minerals.Statistically significant results were obtained for body gains of fat and energy, and decrease in heat production, in the order of increasing fat content of the diets in two 70-day body balance experiments in comparisons made between litter-mate animals.The energy expense of utilization (heat increment) of diets containing from 2 to 30% fat varied from 36 to 16%, respectively, of the gross energy of the diets as determined in two experiments involving the Haldane respiratory quotient procedure. The fat content of the diet had little effect on nitrogen utilization, caused slight decreases in metabolizable energy, but was responsible for larger decreases in heat production as the level of fat in the diet increased. The fat therefore conferred economy of utilization of food energy. The time of day which the heat increments were measured was eliminated as a possible factor in the determination of results.Decreasing the protein content of the diets from the usual 22% level to 7% did not change previous results and again indicated a better utilization of the high fat diets as determined by the body balance method. Increased weight gains, including increased gains of fat and energy, and decreased heat production were associated with the high fat diet.The portion of the heat production due to normal voluntary activity was found to vary in a reciprocal manner with the heat increment—the lower heat increment of the high fat diets being associated with more activity.A study was made of the variations in heat production and activity throughout the day.