The effect of oral essential amino acids on incretin hormone production in youth and ageing

BACKGROUND: The effect of substantive doses of essential amino acids (EAA) on incretin and insulin production, and the impact of age upon this effect, is ill-defined. METHODS: A 15-g oral EAA drink was administered to young (N = 8; 26 ± 4.4 years) and older (N = 8; 69 ± 3.8 years) healthy volunteers. Another group of younger volunteers (N = 9; 21 ± 1.9 years) was given IV infusions to achieve equivalent plasma amino acids (AA) profiles. Plasma AA, insulin, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) were quantified over 2 hours. RESULTS: In younger recruits, EAA-induced rapid insulinaemia and aminoacidaemia with total amino acids(AA), EAA and branched chain amino acids (BCAA) matched between oral and IV groups. Insulin peaked at 39 ± 29 pmol L^-1 at 30 minutes following oral feeding compared to 22 ± 9 pmol L^-1 at 60 minutes following IV feeding (P: NS). EAA peaked at 3395 μmol L^-1 at 45 minutes during IV infusion compared to 2892 μmol L^-1 following oral intake (Feeding effect: P < 0.0001. Oral vs IV feeding: P: NS). There was an 11% greater increase in insulin levels in the 120 minutes duration of the study in response to oral EAA as opposed to IV EAA. GIP increased following oral EAA (452 pmol L^-1 vs 232 pmol L^-1, P < 0.05). Age did not impact insulin or incretins production. CONCLUSION: Postprandial rises in EAA levels lead to rapid insulinaemia which is higher with oral compared with IV EAA, that is attributed more to GIP and unaffected by age. This finding supports EAA, on their own or as part of high-protein meal, as nutritive therapeutics in impaired glycaemia and ageing.