The relationship of carbohydrate metabolism to protein metabolism

EARLIER observations showed that the provision of excess of energy in the human diet is attended by a storage of N and S, the storage being more marked when the surfeit is in the form of carbohydrate than when in the form of fat [Cuthbertson & Munro, 1937].Simultaneously with these observations, it was demonstrated by Larson & Chaikoff [1937] in one-day superimposition experiments on dogs, that this storage was only provoked by carbohydrate ingested within 4 hr.before or after the protein meal.Moreover, the closer the proximity in time of the surfeit carbohydrate to the meal, the greater was the quantity of N stored.These effects of surfeit carbohydrate on protein metabolism prompted us to investigate the function of the total carbohydrate of the ordinary adequate diet, as it affects N metabolism, especially with regard to the relative times of ingestion of the protein and the carbohydrate.The present investigation of protein meta- bolism is divided into four sections:(I) The effect of complete separation as regards time of ingestion of all, or practically all, the carbohydrate and the protein of an adequate diet (Exps.1-5).(II) The effect of separation of only a part of the protein from the carbo- hydrate in such a diet (Exp.6).(III) The effect of taking surfeit carbohydrate at a time separated from that of the ingestion of the protein (Exp.7).(IV) The effect on N balance of varying the number of meals in a fixed diet (Exp.8).(This is intended as a control for certain aspects of the other experi- ments.) EXPERIMENTALThe analytical procedures were similar to those referred to in a previous paper [Cuthbertson & Munro, 1937].The fluid intake was kept as constant as possible throughout these experiments. I. Separate ingestion of dietary protein and carbohydrateExps. 1 and 2. In preliminary experiments, two adults, A. H. S. and H. B. C. (Table I), were put on diets adequate for maintenance, containing 80 g. protein and 2740 cal. in the case of the former, and 97 g. and 3400 cal. in the case of the latter.During Period I this food was divided for both subjects into four equal mixed meals, taken at 8.30 a.m., 1 p.m., 4.30 p.m. and 10 p.m. respectively (Tables II and III).Their body-weights remained constant under this regime.( 128 )