Older adults have delayed amino acid absorption after a high protein mixed breakfast meal

Objectives: To measure the postprandial plasma amino acid appearance in younger and older adults following a high protein mixed meal. Design: Cross-sectional study. Setting: Clinical research setting. Participants: Healthy men and women aged 60-75 (n=15) years, and young controls aged 20-25 years (n=15) matched for body mass index and insulin sensitivity based on the homeostatic model assessment of insulin resistance. Intervention: High protein mixed meal of complete food products. Measurements: Circulating amino acid concentrations were determined hourly before and for 5 hours after meal ingestion. Results: There was no difference between cohorts in postprandial appearance of non-essential amino acids, or area under the curve of any individual amino acid or amino acid class. However, older adults had higher baseline concentrations of aspartic acid, glutamic acid, glycine, ornithine, threonine and tyrosine and lower baseline concentrations of hydroxyproline, isoleucine, leucine, methionine and valine compared to younger adults. Younger adults showed peak essential (EAA) and branched-chain amino acid (BCAA) concentrations at 1 hour post meal while older adults’ peak EAA and BCAA concentration was at 3 hours. Similarly, peak total amino acid concentrations were at 3 hours in older adults. Conclusion: Older adults digested and absorbed the protein within a mixed meal more slowly than younger adults. Delayed absorption of AA following a mixed meal of complete food products may suppress or delay protein synthesis in senescent muscle.