Do you struggle with fatigue? Has your training been getting more intensive? Runners or professionals (salespeople, pharmacists, coaches, etc.): you may have already been advised to start supplementing your diet with glutamine. First used by bodybuilders, consumption of glutamine has emerged as common practice among runners as well. However, the desired effects of glutamine supplementation appear to vary. Perhaps you have questions concerning its mode of action, efficacy, or safety? In this article, you will find the answers to all your questions on the subject of glutamine.
What is glutamine?
Glutamine is a non-essential amino acid. Amino acids are the building blocks of proteins. They are deemed as non-essential when they are produced naturally by the body from other amino acids, which means it is not necessary to ingest them via food. So, then, why ingest glutamine? Simply put: this amino acid, although not essential, can still be beneficial to consume.
Skeletal muscles (muscles that enable skeletal movement) are the primary producers of glutamine , which serves several purposes within the organism:
- immune system functionality
- preservation of digestive tract (which running takes a toll on)
- attenuation of the inflammatory response
- stimulation of protein synthesis (significantly impacted by physical exercise)
- involved in the synthesis of an antioxidant compound glutathione
- contributes to the reconstitution of glycogen and glucose reserves (the main energy substrates of athletes)
Where is glutamine found?
Naturally present in meat, fish, dairy products, legumes and cereals, it is a popular dietary supplement among athletes. It is commonly sold in capsule or powder form, or otherwise included as a component of protein supplements (whey, isolate, BCAAs, etc.). Glutamine is derived from a bacterial fermentation process (similar to cheese) before it is isolated as L-Glutamine . This process typically takes place inside a closed enclosure that is pressurized and sterilized, keeping the risk of contamination low.
Glutamine and fitness improvement
For prolonged exercise sessions (longer than 1h), a normal decrease in the body’s glutamine level occurs, returning to its base level within a few hours of the recovery period. The idea behind glutamine supplementation is to restore blood levels more quickly and thereby optimize physical recovery.
Myth or reality?
- Immune system: After a prolonged session of physical activity, the immune system slightly weakened, making the body more vulnerable to infection, particularly the upper respiratory tract [3,4,5,6]. The hypothesis is that glutamine supplementation potentially strengthens the immune system. Scientific studies have challenged this idea—and, unfortunately, there is no evidence to support the hypothesis [3,6,7,8,9].
- Muscles: As you likely are aware, during physical activity, repeated muscular contractions contribute to the production of lactic acid as well as microlesions in the muscle fibers. After a long run, recovery must occur to repair the damaged muscles. Glutamine that is ingested is mainly used by the cells of the intestines and the liver, which means it is not able to participate significantly in muscle repair.
- Energy reserves: The energy needed for physical exertion is fed to the muscles in the form of glucose. When blood glucose is no longer sufficiently present, the liver supplies the glucose which is stored in the form of glycogen (see article on metabolism). During recovery, the consumption of glutamine together with a sugary drink (high in glucose) makes it possible to reconstitute the liver’s glycogen supply more rapidly .
- Digestive system: For runners, the GI tract endures repeated shocks resulting in a lack of blood flow. This results in microlesions, an inflammatory issue, in addition to possible small, short-lasting hemorrhages. Glutamine supplementation could play a protective role in such cases .
Glutamine—or, how to make your muscles lazy
“The greater the wealth of a people, the lazier these people become.” (Samuel Ferdinand-Lop)
The same phenomenon applies to the human organism: the more glutamine you provide your body, the less you will count on your body to produce it naturally. Moreover, since ingested glutamine is mainly used by the intestines and the liver, the muscles will be the ones drawing the short end of the straw (deficit).
To make matters worse, the nutrients you consume are also competing against each other. If one of them—glutamine, for example—is ingested in large quantities via the digestive system, it will prevent other nutrients from passing through the intestinal mucosal barrier. Ironically, the supplementation may lead to a deficit in competing nutrients.
Experts’ opinion on glutamine
Although some studies speak to the benefits of glutamine supplementation on athletic recovery, the evidence is still lacking. It would therefore be premature to say that supplementation is necessary, especially considering that over the long-term it would not come without side effects (increased risk of cancer, kidney disease, metabolic disorder, etc.) .
Now that you are an expert on the subject of glutamine, decide for yourself how to go forward!
Camille Lamy – Experts in sports nutrition
 De Macar-Culée, A. (2018). Effets d’une supplémentation en glutamine chez des nageurs de haut niveau.
 Kusumoto, I. (2001). Industrial production of L-glutamine. The Journal of nutrition, 131(9), 2552S-2555S.
Castell, L. M., Poortmans, J. R., Leclercq, R., Brasseur, M., Duchateau, J., & Newsholme, E. A. (1996). Some aspects of the acute phase response after a marathon race, and the effects of glutamine supplementation. European journal of applied physiology and occupational physiology, 75(1), 47-53.
Castell, L. M. (2003). Glutamine supplementation in vitro and in vivo, in exercise and in immunodepression. Sports medicine, 33(5), 323-345.
Castell, L. M., & Newsholme, E. A. (1997). The effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise. Nutrition, 13(7-8), 738-742.
Gleeson, M. (2008). Dosing and efficacy of glutamine supplementation in human exercise and sport training. The Journal of nutrition, 138(10), 2045S-2049S.
Mackinnon, L. T., & Hooper, S. L. (1996). Plasma glutamine and upper respiratory tract infection during intensified training in swimmers. Medicine and science in sports and exercise, 28(3), 285-290.
Kingsbury, K. J., Kay, L., & Hjelm, M. (1998). Contrasting plasma free amino acid patterns in elite athletes: association with fatigue and infection. British journal of sports medicine, 32(1), 25-32.
Castell, L. M., Newsholme, E. A., & Poortmans, J. R. (1996). Does glutamine have a role in reducing infections in athletes?. European journal of applied physiology and occupational physiology, 73(5), 488-490.
Bowtell, J. L., Gelly, K., Jackman, M. L., Patel, A., Simeoni, M., & Rennie, M. J. (1999). Effect of oral glutamine on whole body carbohydrate storage during recovery from exhaustive exercise. Journal of Applied Physiology, 86(6), 1770-1777.
Zuhl, M. N., Lanphere, K. R., Kravitz, L., Mermier, C. M., Schneider, S., Dokladny, K., & Moseley, P. L. (2013). Effects of oral glutamine supplementation on exercise-induced gastrointestinal permeability and tight junction protein expression. Journal of applied physiology, 116(2), 183-191.
Holecek, M. (2013). Side effects of long‐term glutamine supplementation. Journal of Parenteral and Enteral Nutrition, 37(5), 607-616.
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