Glutamine: as a dietary supplement for immunity and gut health?

L-glutamine is a non-essential amino acid found in the human body in the largest quantities – it constitutes the most abundant share of free amino acids in both skeletal muscle and blood plasma. This amino acid is often attributed with anabolic and immunostimulatory properties as a dietary supplement, but how does modern sports science view this?

Biological functions of glutamine

• Nitrogen transport: Serves as the primary means of nitrogen transfer between tissues.
• Immune support: It is a primary energy source for immune system cells (lymphocytes) and intestinal mucosal cells.
• Antioxidant precursor: It is essential for the synthesis of glutathione, one of the most important internal antioxidants protecting cells from damage.

Manufacturer's Promises vs. Scientific Reality

Dietary supplement manufacturers attribute a wide range of effects to glutamine, from dramatic muscle growth to immediate performance enhancement and improved immunity. However, according to high-quality scientific sources, the situation is as follows:

Immune System and Disease Prevention

After exhaustive exercise (e.g., a marathon), blood glutamine levels drop sharply, which is associated with a temporary weakening of immunity and a higher risk of infections.

• Positive findings: A study showed that oral administration of 5g of glutamine immediately after a marathon and another dose 2 hours later led to a significant reduction in the incidence of upper respiratory tract infections (common cold) in the week following the race.
• Limitations: Other laboratory studies on immunity markers directly during exercise did not confirm a clear effect of supplementation.

Digestive Tract Health

Glutamine plays a crucial role in maintaining intestinal barrier integrity. Supplementation can improve the function of the intestinal barrier system and reduce the risk of endotoxemia (the penetration of toxins from the intestines into the bloodstream), which can occur during intense physical exertion in heat.

Muscle Glycogen and Recovery

• Glycogen: There is evidence that glutamine may support muscle glycogen synthesis after exercise. However, sources state that if an athlete consumes sufficient carbohydrates and essential amino acids, adding glutamine alone is unlikely to provide any additional benefit.
• Muscle soreness (DOMS): No robust evidence supports claims that glutamine reduces post-workout muscle soreness more effectively than a placebo.

Dosage and Safety

Normal daily glutamine intake from diet ranges around 3 to 6 g. Supplementation is considered safe and well-tolerated.

• Recommendation: For immune support after extreme exertion, literature suggests a dosage of around 0.1g per kg of body weight (approx. 7–10g for an average athlete) in several doses.
• Risks: Extremely high doses exceeding 1g per kg of body weight daily may cause gastrointestinal discomfort in some individuals.

Conclusion for Athletes

Glutamine is an excellent supplement for supporting immune health and gut integrity, especially for endurance athletes during periods of high training load or after competitions. However, its direct impact on increasing muscle strength or accelerating glycogen replenishment (with adequate intake of other nutrients) is minimal according to current science.

────────────────────────────────────────────────────────

Sources of information

1. Nieman, D.C., and B.K. Pedersen, eds. 2000. Nutrition and exercise immunology. Boca Raton, FL: CRC Press.
   
2. Parry-Billings, M., R. Budgett, Y. Koutedakis, E. Blomstrand, S. Brooks, C. Williams, P.C. Calder, S. Pilling, R. Baigrie, and E.A. Newsholme. 1992. Plasma amino acid concentrations in the overtraining syndrome: Possible effects on the immune system. Med Sci Sports Exerc 24(12):1353-1358.
3. Rennie, M.J., P.A. MacLellan, H.S. Hundal, B. Weryl, K. Smith, P.M. Taylor, C. Egan, and P.W. Watt. 1989. Skeletal muscle glutamine concentration and muscle protein turnover. Clin Exp 38:47-51.
4. Jeukendrup, A., & Gleeson, M. (2025). Sport nutrition (4th ed.). Human Kinetics.
   
5. Ardawi, M.S.M., and E.A. Newsholme. 1994. Glutamine metabolism in lymphoid tissues, edited by D. Haussinger and H. Sies, 235-246. Berlin: Springer-Verlag.
6. Bowtell, J.L., K. Gelly, M.L. Jackman, A. Patel, M. Simeoni, and M.J. Rennie. 1999. Effect of oral glutamine on whole body carbohydrate storage during recovery from exhaustive exercise. J Appl Physiol 86:1770-1777.
7. Silva, A.C., M.S. Santos-Neto, A.M. Soares, M.C. Fonteles, R.L. Guerrant, and A.A. Lima. 1998. Efficacy of a glutamine-based oral rehydration solution on the electrolyte and water absorption in a rabbit model of secretory diarrhea induced by cholera toxin. J Pediatr Gastroenterol Nutr 26(5):513-519.
8. Phillips, G.C. 2007. Glutamine: The nonessential amino acid for performance enhancement. Curr Sports Med Rep 6(4):265-268.
9. Borsheim, E., K. Tipton, S. Wolf, and R. Wolfe. 2002. Essential amino acids and muscle protein recovery from resistance exercise. Am J Physiol Endocrinol Metab 283(4):E648-E657.
10. Wilkinson, S.B., P.L. Kim, D. Armstrong, and S.M. Phillips. 2006. Addition of glutamine to essential amino acids and carbohydrate does not enhance anabolism in young human males following exercise. Appl Physiol Nutr Metab 31(5):518-529.
11. Walsh, N.P., A.K. Blannin, P.J. Robson, and M. Gleeson. 1998. Glutamine, exercise and immune function: Links and possible mechanisms. Sports Med 26:177-191.
12. Castell, L.M., J.R. Poortmans, and E.A. Newsholme. 1996. Does glutamine have a role in reducing infections in athletes? Eur J Appl Physiol 73:488-490.
13. Castell, L.M., J.R. Poortmans, R. Leclercq, M. Brasseur, J. Duchateau, and E.A. Newsholme. 1997. Some aspects of the acute phase response after a marathon race, and effect of glutamine supplementation. Eur J Appl Physiol 75:47-53.
14. Gleeson, M., and N.C. Bishop. 2000b. Modification of immune responses to exercise by carbohydrate, glutamine and antioxidant supplements. Immunol Cell Biol 78:554-561.
15. Gleeson, M. 2008. Dosing and efficacy of glutamine supplementation in human exercise and sport training. J Nutr 138(10):2045S-2049S.