Sunday, October 25, 2009



Glutamine is the most abundant amino acid in the body – comprising approximately half of the free amino acids in the blood and muscle. As a non-essential amino acid, glutamine can be produced in the body by conversion from another amino acid - glutamic acid (primarily by the skeletal muscle and liver). Glutamine’s main functions in the body include serving as a precursor in the synthesis of other amino acids and for conversion into glucose for energy. Cells of the immune system, the small intestine and the kidney are the major consumers of glutamine – making “immune boosting” and “immune maintenance” claims for glutamine supplements quite common. In addition, and peripherally related to the control of immune response and inflammation, are claims for glutamine supplements in maintaining muscle mass, reducing post-exercise catabolism (muscle tissue breakdown), and accelerating recovery from intense exercise.

Intense exercise training results in a well-described drop in plasma glutamine levels. Chronically low glutamine levels have been implicated as a possible contributing factor in athletic overtraining syndrome as well as the transient immunosuppression and increased risk of infections that typically affects competitive athletes during intense training and competition. Under conditions of metabolic stress, the body’s need for glutamine may become “conditionally essential” – exceeding its ability to produce adequate levels and meaning that a dietary source is required to prevent catabolism of skeletal muscle – the primary source of stored glutamine in the body.


Glutamine supplements are relatively inexpensive compared to other amino acid supplements. For anybody exposed to heightened levels of stress, such as those recovering from injury, surgery, or intense exercise, glutamine supplements represent an economical way to promote tissue repair, reduce muscle catabolism and help prevent infections.

Scientific Support

A significant body of scientific literature exists to support the beneficial effects of glutamine supplementation in maintaining muscle mass and immune system function in critically ill patients and in those recovering from extensive burns and major surgery. When plasma glutamine levels fall, skeletal muscles may enter a state of catabolism in which muscle protein is degraded to provide free glutamine for the rest of the body. Since skeletal muscle is the major source of glutamine (other than the diet), prolonged deficits in plasma glutamine can lead to a significant loss of skeletal muscle protein and muscle mass. Post-surgical deposition of collagen (a marker for “wound healing”) can be enhanced by amino acid supplementation containing 14 grams of glutamine (Williams et al. 2002), but a lower dose of mixed amino acids containing glutamine (2.9 grams) provided no change in athletic performance or on adaptations to cycling training (Vukovich et al. 1997).

In recent years, several studies have been conducted on glutamine supplementation in athletes and a strong rationale exists for the efficacy of glutamine supplements in athletic populations. For example, glutamine’s role in immune system support has been shown to prevent infections following intense bouts of physical activity (which tend to reduce plasma glutamine levels). Glutamine supplements have also been shown to play a role in counteracting the catabolic (muscle-wasting) effects of stress hormones such as cortisol, which are typically elevated by strenuous exercise. Under conditions of stress-induced protein wasting in adults and children, including burns, post-surgery, and some forms of cancer, glutamine supplementation is associated with reduced protein (muscle tissue) breakdown (des Robert et al. 2002), enhanced lymphocyte function (Yoshida et al. 2001), reduced gut permeability (Klimberg et al. 1992, van Acker et al. 2000, Yoshida et al. 1998, Yoshida et al. 2001), and reduced infections (Barbosa et al. 1999, Burke et al. 1989, O’Riordain et al. 1996). It is interesting to note that although glutamine supplementation has shown benefits in maintaining immune system function and enhancing tumoricidal effectiveness in rodents of during chemotherapy and radiotherapy in various types of cancer (Klimberg et al. 1992), glutamine is also described as an essential factor for tumor growth and as an especially avid consumer of glutamine (Medina 2001, Souba 1993).

The function of glutamine in stimulating glycogen synthase, the enzyme which controls the synthesis and storage of glycogen fuel storage in muscles and liver, may provide a mechanism by which glutamine supplements promote enhanced fuel stores. Glutamine is also thought to increase cell volume, where it may stimulate the activity of enzymes in the liver and muscles involved in glycogen storage as well as those involved in anabolic activities such as protein synthesis. Glutamine supplements have also been hypothesized to increase levels of growth hormone, which may be expected to help stimulate protein synthesis and encourage gains in muscle mass and strength, but reliable evidence for this effect of glutamine supplements has not been demonstrated by clinical studies.

Safety / Dosage

Glutamine supplements are well tolerated at levels up to at least 20 grams per day and intakes of as much as 40 grams per day should induce no significant adverse effects outside of mild gastrointestinal discomfort. As with any isolated amino acid supplement, consumption in divided doses throughout the day should increase total body stores without posing significant absorption issues. For the immune system support and anti-catabolic actions that are of interest to most athletes, recommended doses range from 1-10 grams.


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EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS.

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