The Utilization of Energy Producing Nutriment and Protein as Affected by Individual Nutrient Deficiencies

Abstract

Twenty young growing rats were fed for 14 weeks, by the paired-feeding method, to demonstrate the ways in which cystine affects the utilization of food nitrogen and energy when added to a cystine-deficient diet. The diets compared contained 8 per cent of protein, from skim milk powder; one diet was supplemented with 0.24 per cent of l-cystine. Cystine deficiency unfavorably affected the appetite, but was without certain effect on the digestibility of the food protein. The rats which received the additional 0.24 per cent of cystine made the greater growth, and stored 10.8 per cent more energy and 24.4 per cent more nitrogen than did the controls. During the 14 weeks, the rats which received the cystine stored on the average 40.4 Cal. more than did the controls. This gain was accompanied by 29 Cal. less loss in heat, 8.6 Cal. less loss in feces, and 2.8 Cal. less loss in urine, by the rats which received the cystine supplement. These differences in energy loss, when related to the gross energy of the diets, were 0.1 per cent as urine, 0.3 per cent as feces, and 1.0 per cent as heat. The ratio of carbon to nitrogen in the urine was approximately 2.0, and did not differ significantly between the two groups. The unusual magnitude of this value was due to the low proportion of protein in the diet.