The Effect of Dietary Fat and Caloric Restriction on Protein Utilization

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Abstract
These experiments demonstrate that the incorporation of large amounts of fat in the diet does not alter the utilization of dietary protein when the caloric intake is at an optimal level. Nitrogen utilization may be reduced, however, when large amounts of fat are fed in conjunction with diets restricted in calories and protein. The addition of large amounts of protein to calorically deficient diets results in the use of some of the protein for energy purposes but prevents an increased excretion of nitrogen caused by high-fat diets. The average dog can digest large amounts of protein and fat, but digestibility of fat decreases with depletion of body protein. When dogs are subjected to caloric deprivation, they may be maintained in positive balance for variable lengths of time provided the quantity of dietary protein is sufficient and the caloric reserves of the body are adequate. Continued caloric restriction, however, eventually leads to marked loss of weight and an increase in the excretion of body and dietary nitrogen associated with severe tissue destruction. The role played by the caloric reserves of the body on the resistance of dogs to caloric restriction are discussed. The data also indicate the need for careful evaluation of nitrogen balance studies so that the variables of physiological state and composition of the diet are comparable.