Almost 20% of our body is made up of protein, proving the important role of this macro-nutrient. Proteins consist of many attached smaller units, the amino-acids. One of these amino-acids and the most abundant in the bloodstream is glutamine, also known as L-glutamine. (1)
What is glutamine?
Glutamine is characterized as a semi-essential amino-acid. It is mainly a non-essential because it can be synthesized in the body. However, during stress conditions, the synthesized amounts are not adequate to meet the body’s needs. Thus, in several cases extra supplementation and intake through nutrition is mandatory, therefore it is considered as semi-essential amino-acid. (2)
Glutamine plays a key role as the main carrier of nitrogen between organs. It is a very important nutrient, participating in many processes like synthesis of proteins, nucleic acids and lipids, metabolism, redox homeostasis and others. (3)
How is glutamine made in the body?
Glutamine is synthesized in the body by glutamate with the help of an enzyme called glutamine synthetase and the contribution of ammonia. (4)
In healthy individuals, glutamine is mainly released by the skeletal muscle. Another organ that contributes significantly in glutamine release are the lungs. Furthermore, the adipose tissue could become an important source of glutamine. On the other hand, the liver has a dual role to synthesize or catabolize glutamine. Additionally, the gut and the kidney are considered as the organs where massive glutamine consumption occurs. Moreover, human studies have shown that organs of the gastrointestinal tract and mainly the small intestine, are significant consumers of glutamine. (5)
Studies have shown that glutamine stores may become depleted in catabolic conditions like infections, injuries or long-term use of drugs like glucocorticoids. Therefore, glutamine’s needs are increased for certain groups of people like low birthweight infants, cancer patients, postoperative patients, athletes and others. (6)
Sources of glutamine
Some of the foods that contain glutamine are meat (pork, poultry, beef), dairy (milk, cottage cheese, yogurt) and some vegetables like cabbage, spinach and parsley. Additionally, there are supplements in the form of tablets, powders, capsules or liquid, that provide L-glutamine alone or as glutamine in a protein supplement. (7)
Glutamine & Its Role In Health
According to an academic book on clinical nutrition, glutamine and arginine are the amino acids that have been proved to boost the immune system. Therefore, they are prescribed for post-operative patients and patients in septic conditions. (8)
In a study among athletes, researchers examined the levels of infection in more than 200 runners after strenuous exercise. They concluded that glutamine supplementation after a marathon improved immunity and reduced the incidence of upper respiratory tract infections during the week after the marathon. (9)
Studies show that cancer patients have low plasma glutamine levels. Therefore, supplemental glutamine is prescribed to cancer patients during chemotherapy or radiation treatments. A 2010 published review concluded that exogenous glutamine supplementation is safe and could be beneficial on patients under chemotherapy and radiation. Moreover, researchers reported that glutamine may affect positively patients undergoing bone marrow transplantation. (10)
Gut-Irritable Bowel Syndrome-Crohn’s Disease
A recently published article highlighted the role of glutamine as an essential nutrient for small intestine function. Specifically, glutamine inhibits the death of intestinal cells and has an anti-inflammatory role in the intestine. This protective role possibly occurs by modulating intestinal barrier function under stressful and inflammatory conditions. (11)
An earlier published review mentioned similar findings about the importance of glutamine for maintenance of the intestinal mucosal barrier by several mechanisms such as regulating gene expression, immunity responses and others. This review also highlighted the importance of glutamine on gut function, characterizing glutamine as “a nutritionally essential amino acid for neonates and a conditionally essential nutrient for adults”. (12)
Head injury and Glutamine
Recent studies of head injured patients have shown that glutamine supplementation provides significant benefits and leads to decreased mortality and duration of hospital stay. These studies also showed that supplementation of a formula containing glutamine and probiotics results to limited infections and reduces the patients stay in the intensive care unit. (8)
Muscle growth and prevention of muscle wastage
In a study among 16 healthy participants (men and women) researchers tried to evaluate the impact of glutamine supplementation on muscle strength and soreness after eccentric exercise. They found that L-glutamine supplementation resulted in faster recovery of peak torque and reduced muscle soreness after the exercise. According to the results, the effect was greater in men than women. (13)
Aging is followed by a progressive muscle mass loss which is caused mainly by a loss of skeletal muscle protein. Thus, this condition may be considered as a catabolic state. Therefore, protein and amino acid supplementation like glutamine, may have potential role in the prevention of muscle mass loss during aging. (11)
In a 2007 study, researchers investigated the effects of glutamine supplementation during a high fat diet in adipose tissue and insulin sensitivity in the rat. They reported that glutamine supplementation reduces fat mass. Additionally, they highlighted that glutamine supplementation resulted to increased insulin-stimulated glucose uptake in skeletal muscle and attenuated insulin resistance. (14)
To sum up, glutamine is an amino-acid involved in many body processes. As a supplement, it was firstly used in clinical cases such as adult trauma patients and in very low birthweight infants. Studies have shown that in catabolic and stressful conditions, our body cannot produce the amount of glutamine that it needs. Thus, in several clinical and physiological conditions, glutamine supplementation is necessary to overcome the extra needs and meet the personal requirements. Glutamine alone or added to any amino acid nutritional supplementation may contribute to the preservation of the gut and improved gut function. Therefore, glutamine should not be considered only as a supplement for clinical conditions, but as an essential nutrient that promotes well-being and immunity of healthy individuals.
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8) Katsilambros, N., Dimosthenopoulos, C., Kontogianni, M., Manglara, E. and Poulia, K. (2011). Clinical Nutrition in Practice. 1st ed. Somerset: Wiley.
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