In 1999 over $16 billion was spent on dietary supplements with $1.42 billion representing the sports supplements industry. I am constantly perplexed by how many of us are unaware of what we are buying, why we are buying it, and whether or not there is evidence that it truly works aside from the big, beefy guy in the gym swearing up and down by its use.
This is a disconcerting phenomenon, especially in light of the fact that there is such little regulation by the Food and Drug Administration (FDA) on dietary supplements. In this article I hope to shed some light on the role of glutamine as a sports supplement and provide some evidence as to its efficacy.
What Is Glutamine?
Glutamine is the most abundant non-essential amino acid in the body. It is found in large quantities in skeletal muscle and plasma and has many functions, including the transfer of nitrogen between organs and the detoxification of ammonia, acid-base regulation in the body, a precursor to the synthesis of nucleotides and a fuel for cells of the gut lining and immune system (Rowbottom, 1996).
Its effects are classified as anabolic as well as immunostimulatory. I would bet a year's supply of glutamine that if you were to ask someone in the gym what glutamine does, that person would respond, "It helps the immune system." Glutamine is most famous in the sports industry for its role in immunity. Other claims being made about glutamine include its cell "volumizing" effect, stimulation of muscle protein synthesis, glycogen repletion and synthesis, improved muscle repair, decreased muscular soreness. and improved high-intensity performance (Kreider, 1999).
How Does It Work?
Skeletal muscle is a major player in the release of glutamine during times of need. It has even been hypothesized that skeletal muscle releases the majority of glutamine into plasma when required by other tissues (Rowbottom, 1996). However, during these times of extreme need, as in the case with the overtraining syndrome (OTS) and intense exercise, more glutamine is required than the body is able to produce. This is why glutamine has been declared a "conditionally" essential amino acid.
It is during these times that it is necessary to supplement because the body cannot synthesize enough to meet demands. Glutamine supplementation is also used in patients suffering from gastrointestinal disorders such as Crohn's disease, irritable bowel syndrome (IBS) and peptic ulcers because the lining of the gastrointestinal tract has the highest turnover of cell production and preferentially uses glutamine stores. It is also used for the treatment of AIDS, cancer, burn victims, autoimmune diseases, fibrosis, stress, fatigue, and alcoholism. It has also been suggested that glutamine stimulates the release of growth hormone (Welbourne, 1995).
During times of heavy, intense exercise plasma glutamine levels decline and it is this decline that has been associated with an increase in the rate of infection among athletes (Parry-Billings, 1992). This leads to specific organs and tissues in the body not receiving enough of glutamine in order to function optimally.
These organs and their mechanisms include: the kidneys so as to maintain acid-base balance in the body, the liver in order to synthesize glycogen and other compounds such as the endogenous antioxidant, glutathione, the production of cells of the immune system, and the gastrointestinal tract and the brain so as to detoxify cerebral ammonia (Rowbottom, 1996). It has also been suggested that intramuscular stores of glutamine are related to the rate of protein synthesis as well as the promotion of glycogen synthesis (Bowtell, 1999).
What Evidence Supports These Claims?
In a study by Bowtell et al., in 1999 seven male subjects were fatigued to exhaustion in order to deplete all muscle glycogen stores. This exercise protocol involved the recruitment of both type I and type II fibers by incorporating long duration, aerobic exercise with short bursts of maximal effort intensity work. Each subject was given one of three drinks post-exercise: 330 mL glucose-polymer solution, 330 mL glucose-polymer solution with 8g glutamine or 330 mL placebo with 8g glutamine.
Measurements were taken incrementally during the 2 hours of post-exercise recovery. What was discovered was that plasma glutamine concentrations were highest post-exercise in the glutamine containing drinks suggesting that glutamine supplementation prevents exercise-induced immunosuppression.
What was also discovered was that oral glutamine supplementation alone promoted glycogen storage similar to that of the glucose-polymer drink suggesting glutamine's role in promoting glycogen synthesis after prolonged, exhaustive exercise. What can then be concluded is that a post-exercise meal consisting of optimal amounts of carbohydrate in conjunction with a protein source (or an MRP with glutamine) is the best way to promote muscle glycogen and protein synthesis after a workout.
In another study by Castell and Newsholme in 1997 the effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise was examined. In this data analysis consisting of many different clinical trials, 200 male and female athletes consisting of ultra-marathoners, marathoners, middle distance runners (10k races and/or 15 mile training sessions) and competitive rowers were monitored for infection for 7 days during the training season and after glutamine supplementation. Glutamine (group G) and placebo (group P) feedings were given to the athletes immediately following an exercise bout and 2 hours after.
Plasma levels of glutamine were measured in the athletes in comparison with a group of healthy, non-exercising controls. What was discovered was that during the 7 days after the glutamine and placebo feedings the percentage of athletes reporting no infections was greater in group G (81% reported no infections) compared to group P (49% reported no infections). Infections were categorized into any athlete suffering from colds, cough, sore throat and/or influenza occurring within 1 week of the exercise bout. This data suggests a higher rate of infection after high-intensity exercise that can be mitigated by the inclusion of oral glutamine supplementation after exercise.
Unfortunately, there is not enough research yet supporting the role of glutamine supplementation after high-intensity resistance training. It can be assumed that high-intensity resistance training results in the same type of effect as high-intensity endurance training because of its muscle glycogen depleting mechanisms as well as the intense demand placed onto the body for the synthesis of protein / muscle tissue. It can then be assumed that oral supplementation of glutamine may result in a decreased risk of infection after weight training, an increased rate of muscle glycogen synthesis, improved muscular repair and recovery and reduced soreness.
What Is The Dosage?
Normal intake of glutamine from protein-rich foods is approximately 3 to 6g per day based on a protein intake of 0.8 - 1.6g/kg bodyweight. Therefore, if you are an 80kg male (176lbs) and you are consuming between 64g - 128g of protein per day (and since you are reading Bodybuilding.com, I bet your consumption is a lot more than this...) your glutamine intake from food sources is within this range. To convert your weight from pounds to kilograms, simply take your weight and times it by 0.4536. So if you weight 165 pounds, you would take 165 X 0.4536 to get approximately 75 kilograms.
Researchers examining the effects of high-intensity exercise on plasma concentrations of glutamine are currently using a dose of 0.1g glutamine per kg body weight (that's 8g for our fictitious male bodybuilder, 0.1 X 80) every 30 minutes post-exercise for a 2-3 hour recovery period in order to prevent this decline in plasma glutamine. Manufacturers of glutamine supplements are recommending dosages of 5g post-workout and an additional 5-10g throughout the day "for best results."
There is no way to know for sure exactly how much is enough or how much is too much. There are currently no reported side effects from its use and the evidence supporting the benefits of glutamine supplementation for bodybuilders is promising. Many studies support its role in protein anabolism, prevention of infection after intense exercise, the release of growth hormone and many other mechanisms important in bodybuilding thereby making it a key component in the supplemental stack of our sport.
1. Blanchard, MA, Jordan, G, Desbrow B, MacKinnon LT and Jenkins DG., The influence of diet and exercise on muscle and plasma glutamine concentrations. Med Sci Sports Exerc., Vol. 33, No. 1, 2001, pp. 69-74.
2. Bowtell JL, Gelly K, Jackman ML, Patel A, Simeoni M and Rennie MJ., Effect of oral glutamine on whole body carbohydrate storage during recovery from exhaustive exercise. J Appl Physiol 1999;86:1770-1777.
3. Castell, LM, Poortsman JR and Newsholme EA. Does glutamine have a role in reducing infections in athletes? Eur J Appl Physiol 73.5 (1996):488-90.
4. Castell LM and Newsholme EA., The effects of oral glutamine supplementation on athletes after prolonged exhaustive exercise. Nutrition 13.7-8 (1997):738-742.
5. kreider RB. Dietary supplements and the promotion of muscle growth with resistance exercise. Sports Med. 1999 Feb: 27 (2): 97-100.
6. 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. 1992; 24:1353-1358.
7. Rowbottom, DG, Keast D and Morton AR. The emerging role of glutamine as an indicator of exercise stress and overtraining. Sports Med. 21.2 (1996):80-97.
8. Welbourne TC. Increased plasma bicarbonate and growth hormone after an oral glutamine load. Am J Clin Nutr 61: 1058-1061, 1995.
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