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Title: Defining meal requirements for protein to optimize metabolic roles of amino acids

item LAYMAN, DONALD - University Of Illinois
item ANTHONY, TRACY - Rutgers University
item RASMUSSEN, BLAKE - University Of Texas Medical Branch
item ADAMS, SEAN - University Of Arkansas
item LYNCH, CHRISTOPHER - Pennsylvania State College Of Medicine
item BRINKWORTH, GRANT - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item DAVIS, TERESA - Children'S Nutrition Research Center (CNRC)

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2015
Publication Date: 4/29/2015
Citation: Layman, D.K., Anthony, T.G., Rasmussen, B.B., Adams, S.H., Lynch, C.J., Brinkworth, G.D., Davis, T.A. 2015. Defining meal requirements for protein to optimize metabolic roles of amino acids. American Journal of Clinical Nutrition. 101(Suppl):1330S-1338S.

Interpretive Summary: Protein in the diet provides the body with individual amino acids that cannot be synthesized in the body. These amino acids regulate a number of different functions in the body including the synthesis of body proteins, the immune response, and satiety. The rise in amino acids in the blood after a meal stimulates these different processes through different signaling systems within the body. For example, the rise in the amino acids, leucine, after a meal, stimulates an intracellular signaling pathway that stimulates the synthesis of muscle protein, and this response to leucine decreases as we get older and when we exercise less. The current dietary recommendation for protein is 0.8 gram per kilogram of body weight, but recent research suggests that a higher consumption of more than 1.0 gram per kilogram of body weight may be beneficial for older adults. In addition, consumption of at least 20 to 30 grams of protein at each meal, breakfast, lunch, and dinner, is beneficial to optimize metabolic health.

Technical Abstract: Dietary protein provides essential amino acids (EAAs) for the synthesis of new proteins plus an array of other metabolic functions; many of these functions are sensitive to postprandial plasma and intracellular amino acid concentrations. Recent research has focused on amino acids as metabolic signals that influence the rate of protein synthesis, inflammation responses, mitochondrial activity, and satiety, exerting their influence through signaling systems including mammalian/mechanistic target of rapamycin complex 1 (mTORC1), general control nonrepressed 2 (GCN2), glucagon-like peptide 1 (GLP-1), peptide YY (PYY), serotonin, and insulin. These signals represent meal-based responses to dietary protein. The best characterized of these signals is the leucine-induced activation of mTORC1, which leads to the stimulation of skeletal muscle protein synthesis after ingestion of a meal that contains protein. The response of this metabolic pathway to dietary protein (i.e., meal threshold) declines with advancing age or reduced physical activity. Current dietary recommendations for protein are focused on total daily intake of 0.8 g/kg body weight, but new research suggests daily needs for older adults of =1.0 g/kg and identifies anabolic and metabolic benefits to consuming at least 20-30 g protein at a given meal. Resistance exercise appears to increase the efficiency of EAA use for muscle anabolism and to lower the meal threshold for stimulation of protein synthesis. Applying this information to a typical 3-meal-a-day dietary plan results in protein intakes that are well within the guidelines of the Dietary Reference Intakes for acceptable macronutrient intakes. The meal threshold concept for dietary protein emphasizes a need for redistribution of dietary protein for optimum metabolic health.