Role of nutrients in the regulation of in vivo protein metabolism in humans.

Nutrients regulate protein metabolism both in an acute fashion and on a long-term basis. The ingestion of meals is associated with a dramatic switch from an overall catabolic state to a state of net protein anabolism. The acute response of protein metabolism to meal ingestion is mediated, in part, by an increase in insulin secretion, itself a consequence of glucose absorption. Whereas insulin may primarily suppress rates of proteolysis, amino acids are responsible for the stimulation of protein synthesis that follows food intake. In the long run, the effects of nutrition on protein metabolism depend on the energy supply, the source of the energy (carbohydrate versus fat) and dietary protein intake. Finally, specific amino acids, such as glutamine, may play an additional role as protein anabolic agents.