Amino acid ingestion improves muscle protein synthesis in the young and elderly
Researchers previously demonstrated that an essential amino acid (EAA) supplement delivered intravenously boosted muscle protein synthesis in both young and elderly people. However, 2- to 3-hour continuous delivery does not replicate a realistic supplementation regimen or account for age-related influencers, such as a slower rate of gastric emptying, and intravenous supplementation is invasive as well.
As a workaround, researchers were curious if the same muscle-stimulating benefits could be had with oral ingestion of 15 grams of EAAs, which models a convenient, safe, and replicable supplementation protocol.
Acute metabolic study
Number of Subjects
Young subjects: 30 - 38
Older subjects: 65 - 69
The purpose of this study was to determine if oral ingestion of 15 grams of essential amino acids stimulated muscle protein synthesis to a similar degree in young and elderly individuals.
Researchers calculated muscle protein kinetics and mixed muscle fractional synthetic rate (FSR) before and after the oral ingestion of 15 grams of essential amino acids in young and older participants.
Net phenylalanine balance, which characterizes the relationship between muscle protein synthesis and breakdown, was slower in elderly subjects after taking the essential amino acids, but remained higher for a longer period.
FSR went up in both age groups to a similar extent.
Oral ingestion of 15 grams of essential amino acids stimulated muscle protein synthesis in young and elderly subjects to a similar degree, despite older participants experiencing a more sustained increase in plasma phenylalanine concentration and net phenylalanine balance after EAA ingestion.
This was the first study to evaluate the time course of muscle protein synthesis and analyze muscle protein kinetics after oral ingestion of essential amino acids in the young and elderly. Supplementing with essential amino acids orally is a practical and safe means of increasing muscle protein synthesis in all ages.
Paddon-Jones D, Sheffield-Moore M, Zhang XJ, et al. Amino acid ingestion improves muscle protein synthesis in the young and elderly. Am J Physiol Endocrinol Metab. 2004;286(3):E321-E328. doi:10.1152/ajpendo.00368.2003