Glutamine is an amino acid that has gained popularity among endurance athletes as an important post-workout nutrient. (Amino acids are the building blocks of protein). Many athletes take supplements or consume sports drinks that contain glutamine in order to improve immune function.
Glutamine is an important fuel for immune cells and is typically decreased in the body after endurance exercise. Immune function is known to be lowered after endurance exercise as well, so the idea that supplementing with glutamine post-workout would improve immune function does make sense. However, evidence shows that even when glutamine supplementation is used, immune function still suffers after endurance exercise. In fact, studies have not been able prove that a low level of glutamine in the body causes a higher rate of infections. So, even though there is a reduction in glutamine, and it is used by immune cells for energy, it doesn't appear to be the magic bullet for avoiding infections in the over-trained athletes.
It is interesting to note that immune function does improve in moderately trained individuals, but suffers in sedentary people. Moderation wins again, my friends. (Regardless, I can't tear myself away from marathon training!) Another important point is that glutamine is a non-essential amino acid. That means that your body can manufacture the nutrient all by itself. However, you should definitely increase your calories after a long work-out and include protein. Glutamine is a highly abundant amino acid in many foods including red meat, fish, poultry, legumes, and vegetables. There is no need to buy an expensive supplement or drink that contains this amino acid because we have found that it doesn't show efficacy in improving immune function and you can get it from your regular diet.
Agostini, F. & Biolo, G. Effect of physical activity on glutamine metabolism. Curr Opin Clin Nutr Metab Care. 2010 Jan;13(1):58-64.
Calder PC, Yaqoob P. Glutamine and the immune system. Amino Acids. 1999;17(3):227-41.
Gleeson, M. Dosing and efficacy of glutamine supplementation in human exercise and sport training. J. Nutr. Oct 2008; 138(10):2045S-2049S.
Parry-Billings M, Budgett R, Koutedakis Y, Blomstrand E, Brooks S, Williams C, Calder PC, Pilling S, Baigrie R, Newsholme EA. Plasma amino acid concentrations in the overtraining syndrome: possible side effects on the immune system. Med Sci Sports Exerc. 1992 Dec;24(12):1353-8.
Walsh NP, Blannin AK, Robson PJ, & Gleeson M. Glutamine, exercise, and immune fuction. Links and possible mechanisms. Sports Med. 1998 Sep;26(3):177-91.