The relationship of carbohydrate metabolism to protein metabolism

Abstract

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 metabolism 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 carbohydrate 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 experiments.) EXPERIMENTAL The 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 carbohydrate Exps. 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 bodyweights remained constant under this regime.

337. The supplementary relationships between the proteins of dairy products and those of bread and potato as affected by the method of feeding. With a note on the value of soya-bean protein

“…; in either case the growth was inferior to that observed when the same proportion of the amino acid was incorporated in the diet. More recently, Elman(i5) obtained similar results with dogs, while Cuthbertson and his colleagues (16,17) found that when the protein and carbohydrate fractions of a diet, jointly capable of maintaining nitrogen equilibrium, were given at different times of the day to human adults (16) or adult rats(i7) the nitrogen balance became negative and there was loss of body weight.…”

Interrelationships of nutrients: Chairman's opening remarks

“…T h e presence of carbohydrate in a meal can also influence the subsequent metabolic fate of the amino acids after absorption. Some years ago we noted that nitrogen balance underwent a temporary deterioration when the protein and carbohydrate in a diet were consumed in separate meals, whereas no such change in nitrogen balance followed separation of dietary protein and fat (Cuthbertson & Munro, 1939;Munro, 1949). Subsequent studies (Munro, Black & Thomson, 1959) suggest that the presence of carbohydrate in a meal causes release of insulin which then induces deposition of some of the incoming amino acids in muscle in the form of labile protein.…”