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

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.

Protein “requirements” beyond the RDA: implications for optimizing health

“…The RDA represents the estimated average requirement plus 2 standard deviations, determined from selected nitrogen-balance studies of which very few were performed in older individuals (Rand et al 2003). This approach, which determines the minimal protein intake required to avoid net nitrogen losses, is now considered inappropriate for establishing recommendations (Layman et al 2015). This particularly applies to elderly persons experiencing muscle loss, reduced energy intake and physical activity, and comorbidities, which all affect nitrogen balance and protein anabolism.…”

Global deletion ofBCATmincreases expression of skeletal muscle genes associated with protein turnover

“…49). Paradoxically, increased plasma BCAAs have been shown to be predictive of an increased risk of diabetes mellitus and insulin resistance or have been associated with these disorders (1,7,10,14,21,47,58,63,73,75,84,85,87).…”

Perspective: The Potential Role of Essential Amino Acids and the Mechanistic Target of Rapamycin Complex 1 (mTORC1) Pathway in the Pathogenesis of Child Stunting

“…In humans, evidence for amino acid signaling through the mTORC1 pathway could be provided through future investigations that combine metabolomics with characterization of the proteome and transcriptome. Future work could also be done to explore the concept of a meal-based protein threshold for children (173).…”