What is L-Glutamine?
L-Glutamine is the most abundant amino acid found in muscle. It is a conditionally essential amino acid meaning it is produced naturally by the body; however, at certain times L-Glutamine ingestion via dietary intake is necessary to sustain normal L-Glutamine levels as the body cannot naturally make enough to do so.
Why should you consume L-Glutamine?
Muscle L-Glutamine levels are reduced following endurance exercise lasting longer than two hours(1). Reduced L-Glutamine levels attenuate the body’s immune system response. The release of a signalling molecule, interleukin-6, that stimulates the immune response is suppressed(2), and white blood cell differentiation is reduced(1), which decreases the formation of new cells and reduces immunological function. Ingestion of L-Glutamine appears to alleviate the decline in L-Glutamine levels(3), and potentially reduces immune cell damage(4), and therefore attenuates the reduction in the immune system response following endurance exercise. Ingestion of L-Glutamine is shown to reduce the self-reported incidence of illness in endurance athletes(5). Reduced immune system suppression following exercise decreases the risk of illness and infection which would otherwise cause a reduction in exercise performance.
L-Glutamine ingestion during endurance exercise lasting longer than an hour prevents a significant reduction in L-Glutamine levels which in turn decreases ammonia concentration in the blood(6). L-Glutamine ingestion may therefore be able to attenuate any reduction in performance as a result of reduced L-Glutamine levels or increased ammonia concentration(6). However the effects of L-Glutamine ingestion on endurance exercise performance warrant further research.
When should you consume L-Glutamine?
Based on the available evidence L-Glutamine should be consumed after endurance exercise lasting longer than two hours in order to restore muscle L-Glutamine levels that were decreased during exercise.
Parry-Billings, M., Budgett, R., Koutedakis, Y., Blomstrand, E., Brooks, S., Williams, C., Calder, P. C., Pilling, S., Baigrie, R., & Newsholme, E. A. (1992). Plasma amino acid concentrations in the overtraining syndrome: possible effects on the immune system. Medicine and Science in Sports and Exercise, 24(12), 1353-1358 Hiscock, N., Petersen, E. W., Krzywkowski, K., Boza, J., Halkjaer-Kristensen, J., & Pedersen, B. K. (1985). Glutamine supplementation further enhances exercise-induced plasma IL-6. Journal of Applied Physiology, 95(1), 145-148 Kingsbury, K. J., Kay, L., & Hjelm, M. (1998). Contrasting plasma free amino acid patterns in elite athletes: association with fatigue and infection. British Journal of Sports Medicine, 32(1), 25-32 Cury-Boaventura, M. F., Levada-Pires, A. C., Folador, A., Gorjão, R., Alba-Loureiro, T. C., Hirabara, S. M., Peres, F. P., Silva, P. R., Curi, R., & Pithon-Curi, T. C. (2008). Effects of exercise on leukocyte death: prevention by hydrolyzed whey protein enriched with glutamine dipeptide. European Journal of Applied Physiology, 103(3), 289-294 Castell, L. M., Poortmans, J. R., & Newsholme, E. A. (1996). Does glutamine have a role in reducing infections in athletes?. European Journal of Applied Physiology, 73(5), 488-490 Carvalho-Peixoto, J., Alves, R. C., & Cameron, L. C. (2007). Glutamine and carbohydrate supplements reduce ammonia increase during endurance field exercise. Applied Physiology, Nutrition and Metabolism, 32(6), 1186-1190