Free and protein-bound glutamine have identical splanchnic extraction in healthy human volunteers.
Level 2 - randomized trial
Controlled metabolic tracer trial in healthy human volunteers
PubMed 11408280 · doi:10.1152/ajpgi.2001.281.1.G267
What was done
Eight healthy adults in the postabsorptive state received an 8-hour intravenous infusion of L-[1-13C]glutamine (3 µmol·kg⁻¹·h⁻¹) and L-[1-13C]lysine (1.5 µmol·kg⁻¹·h⁻¹). Four hours into the infusion, participants consumed liquid formula every 20 minutes containing either 2.5 g of protein from 15N-labeled oat proteins or an equivalent mixture of free amino acids containing L-[2,5-15N2]glutamine and L-[2-15N]lysine. Splanchnic extraction of glutamine and lysine was measured and compared between the two formulations.
What was found
Splanchnic extraction of glutamine was 62.5 ± 5.0% for 15N-labeled oat proteins and 66.7 ± 3.9% for the free amino acid mixture. Lysine splanchnic extraction was 40.9 ± 11.9% for oat proteins and 34.9 ± 10.6% for free amino acids. No significant differences were observed between intact protein and free amino acids. Quantitative values for de novo glutamine synthesis were not reported in the abstract.
Why it matters
Enteral glutamine is equally bioavailable whether provided in intact dietary protein or as free amino acids. This indicates that stable, glutamine-rich whole protein sources can be used in enteral nutrition formulas instead of less stable free glutamine supplements.
Limits
The sample size was very small (n = 8) and conducted exclusively in healthy adults, which limits generalizability to critically ill or catabolic clinical populations. The abstract does not specify whether treatment administration was randomized or crossover, nor does it provide quantitative results for de novo glutamine synthesis.
Cited by
- partial When ingested orally, the gut and liver consume the vast majority of glutamine, resulting in very little entering the bloodstream.