Amino Acids Stimulate Muscle Protein Synthesis In The Elderly More Effectively Than Intact Protein

Abstract

PURPOSE To combat the debilitating progression of sarcopenia, a nutritional supplement should provide a calorically efficient anabolic stimulus that does not result in a compensatory reduction in voluntary food intake. We sought to quantify net muscle protein synthesis in healthy elderly individuals following bolus oral ingestion of an intact whey protein supplement (whey: n=5, 70 ± 6 yr) and an essential amino acid supplement (EAA: n= 7, 67 ± 2 yr). METHODS Femoral arterio-venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion of L-[ring-2H5]phenylalanine. Muscle protein kinetics and mixed muscle fractional synthetic rate (FSR) were calculated during the post-absorptive period and for 3 h following ingestion of 15g EAA or 15g whey. RESULTS EAA ingestion stimulated net phenylalanine uptake and FSR more than whey protein. Postabsorptive FSR values were 0.056 ± 0.004 %.hr−1 (EAA) and 0.053 ± 0.004 %.hr−1 (whey), p > 0.05), while postprandial FSR values increased to 0.088 ± 0.011 %.hr−1 (EAA) and 0.072 ± 0.04 %.hr−1 (whey), (p < 0.05). CONCLUSIONS Compared to an equivalent quantity of intact protein, EAAs may provide a more effective and energetically efficient anabolic nutritional supplement for elderly individuals.