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Is Glutamine Supplementation Beneficial for Sport Performance?

Glutamine is the most abundant amino acid in the body. It is often considered a "non-essential" amino acid because it is also manufactured by the body (most importantly skeletal muscle). Glutamine is required as a substrate for energy production and as a nitrogen source for nucleotide synthesis by lymphocytes. Glutamine is a nitrogen donor for the synthesis of purine and pyrimidine nucleotides and is thus essential for protein synthesis and cell proliferation.

Glutamine:

(1) facilitates water and sodium absorption in the gut absorption (Rhoads et al., 1990)

(2) improves mucosal healing from a gastrointestinal infection or after damage from either radio- or chemotherapy;

(3) improves gut and systemic immune function;

(4) may aid in attaining nitrogen balance;

(5) is available in the lumen of the intestine from the digestion of protein; and

(6) is an intestinal epithelial fuel source.

Plasma glutamine is utilized at a very high rate by cells of the immune system and is considered to be an important fuel for them. Low glutamine levels have been associated with immunosuppression during sepsis or following trauma such as surgery or burns.

It appears that during stress the body's glutamine requirements increase considerably. In critically ill patients, glutamine may speed up recovery. The absorptive cells of the small intestine use glutamine at a high rate subsequently little has been observed to enter the bloodstream. To satisfy the other organ demands skeletal muscle synthesizes glutamine.

Glutamine, Exercise, and Skeletal Muscles

Intense physical effort may have a potentially immunosuppressant effect by causing a transient suppression of the immune system. The demands on muscle and other organs are so high during intense physical activity that the immune system may suffer from a lack of glutamine that temporarily affects its function (Newsholme, 1994). It has been suggested that since skeletal muscle is the major tissue involved in glutamine production that skeletal muscle must thus play a vital role in the process of glutamine utilization in the immune cells. Consequently, it has been hypothesized that the activity of the skeletal muscles may directly influence the immune system. For example, endurance runners exhibit a higher incidence of upper respiratory tract infections (URTI) (Heath et al., 1991) and recent reports have shown that plasma glutamine levels decrease acutely after single sessions of high intensity running (Parry-Billings et al., 1992) and after more extended periods of intensive running training (Keast et al. 1995).

Because blood glutamine levels decline after heavy exercise, it is possible that exercise-induced immunosuppression may be caused in part by a glutamine deficiency.

The effects of oral glutamine supplementation on marathon and ultra-marathon runners were tested in a double-blind study. In the seven days following a marathon, 51% of the runners given a placebo developed an infection compared with only 19% of those given 10 grams of glutamine immediately after completing the marathon (Castell and Newsholme, 1997). In a more recent study, the influence of glutamine supplementation on exercise-induced immune system changes was assessed for 3 bouts of bicycle ergometer exercise (Rohde et al., 1998). Oral glutamine supplementation abolished the decrease in plasma glutamine concentration post exercise without influencing any of the immune system parameters. This does not support the hypothesis that decreased plasma glutamine concentrations post exercise causes post-exercise immune system changes.

Overtraining Syndrome and Immunosuppression

The overtraining syndrome in athletes is characterized by poor performance, fatigue and depression, among others. These may persist until the athlete rests. There are no large scale studies that have systematically examined immune function in overtrained athletes yet there has been much interest stimulated as there are many reports of signs of immunosuppression in these athletes, such as a higher incidence of infectious diseases and slower wound healing. Overtrained runners were also found to exhibit significantly lower plasma glutamine concentrations compared with non-overtrained runners training (Keast et al. 1995). Plasma glutamine concentrations were shown to increase slightly over a 4 week period of intensified training in well-trained elite swimmers, but not in those exhibiting symptoms of overtraining. Because of the apparent requirement of lymphocytes for glutamine, it has been suggested that low plasma glutamine levels associated with intensive training and overtraining syndrome may compromise lymphocyte function and possibly contribute to an increased incidence of infectious diseases in competitive athletes. Plasma glutamine concentration however, did not differ between well-trained elite swimmers and those that did not develop upper respiratory tract infections (URTI) during a 4 week period of intensified training, indicating that the appearance of URTI is not related to changes in plasma glutamine concentration during intensified training in elite swimmers (MacKinnon and Hooper, 1995).

Is Glutamine Supplementation of Benefit to Athletes?

At this point there is no definitive research to encourage supplementation with glutamine as a method of boosting immune system function. The bottom line: eat well, ensure lots of variety in your intake, consume sufficient high quality protein to meet your training needs, and rest up to avoid overtraining syndrome.

Bibliography:

Castell LM, Newsholme EA. The effects of oral supplementation on athletes after prolonged, exhaustive exercise. Nutrition 13:738-742, 1997.

Heath, GW, Ford ES, Craven TE, Macera CA, Jackson KL, Pate RE. Exercise and the incidence of upper respiratory tract infection. Med Sci Spo Exerc. 27:741-747, 1991.

Keast D, Arstein D, Harper W, Fry RW and Morton AR. Depression of plasma glutamine concentration after exercise stress and its possible influence on the immune system. Med J Aust. 162:15-18, 1995.

MacKinnon LT, Hooper SL, Hanrahan SJ. Hormonal and immunological responses to intensified training in elite swimmers. Proceedings of the Sports Medicine Australia Annual Scientific Conference in Sports Medicine. Sports Medicicne Australia, Canberra, 1994.

Newsholme EA. Biochemical mechanisms to explain immunosupression in well-trained and overtrained athletes. Int J Sports Med. 15:142-147, 1994.

Parry-Billings M, Budgett R, Koutedakis, Y, Blomstrand E, Brooks S, Williams C, Calder PC, Pilling S, Baigrie R and Newsholme EA. Plasma amino acid concentrations in the overtraining syndrome: possible effects on the immune system. Med Sci Sports Exerc. 24:1353-1358, 1992.

Rhoads JM, Keku EO, Bennett LE, Quinn J Leece JG. Development of L-glutamine-stimulated electroneural sodium absorption in piglet jejunum. Am J Physiol. 1990;259:G99-G107.

Rohde T, Maclean DA, Pedersen BK. Effect of glutamine supplementation on changes in immune system induced by repeated exercise. Med Sci Sports Exerc. 30(6):856-862, 1998.