Glutamine is one of the most freely available amino acids in the body and accounts for approximately 60% of the reservoir of amino acids stored in skeletal muscles. Approximately 90% of glutamine is manufactured by the skeletal muscles themselves with the remaining 10% being produced by the lungs and brain. Because glutamine can be produced by the body in such abundance, it is classified as a ‘non-essential’ amino acid although in some situations it does become essential. Under extreme physical stress for example, the demand for glutamine may exceed its availability and as such the need to consume more from food may present- thus it becomes essential.
Functions of Glutamine:
Glutamine fulfills a variety of functions, including:
- Protein synthesis- the formation of new protein cells from amino acids
- Preservation of muscle tissue- glutamine exerts an anti-catabolic effect which prevents the breakdown of muscle tissue when there is an amino acid shortfall
- Promotes glycogen formation- glutamine has been linked with glycogen synthesis, particularly under starvation conditions
- Transportation of ammonia in the blood plasma (watery component)
- Supports the immune system- the body’s infection fighting cells use glutamine as a source of energy, particularly the lymphocytes (white blood cells)
- Cancer- people with some forms of cancer have demonstrated lower levels of glutamine; for this reason it is speculated that glutamine supplementation may benefit cancer patients undertaking conventional treatment for their condition
- Recovery from stress- the immune supporting effect of glutamine is essential in this process
- Heals the gut and reduces food cravings- glutamine has been shown to calm inflammation of the intestines and significantly helps those suffering from irritable bowel syndrome (IBS)
The anti-catabolic effects of glutamine are so potent that it is commonly used in a clinical setting to counteract the muscle wasting and impaired protein formation that occurs from the long-term use of glucocorticoid (steroid) treatments. Those suffering from conditions like arthritis, asthma, multiple sclerosis and lupus to name a few may therefore benefit from glutamine supplementation.
From an exercise perspective, many competitive and recreational exercisers use glutamine supplements to maintain a healthy immune system and more frequently to promote and maintain lean muscle mass. While glutamine has proven to be effective in achieving both of these objectives in some situations, it does not appear to increase the development of strength and power in those who are trained. The likelihood is that the body’s natural production is adequate to support anabolism (tissue formation) and that taking additional glutamine above the body’s metabolic need is unnecessary.
The concentration of glutamine in the blood plasma usually increases during exercise and decreases post-exercise, especially following prolonged and/or intense exercise, which can cause a temporary glutamine deficiency and reduction in immune function. Those involved in endurance training ‘may’ derive some benefit from glutamine supplementation, especially those who are overtrained because its use has been linked with a reduced susceptibility to upper respiratory tract infections (URTI). Additionally, because glutamine is found in greater concentrations in slow-twitch muscle fibres, evidence suggests that there is a greater need for it to support endurance/aerobic training.
Glutamine supplementation is usually taken in the form of L-glutamine, which is available as an isolated product, or within most general protein or meal replacement products. Common forms of the isolated glutamine include capsules, tablets, and drinks, most of which contain around 500mg per portion.
All glutamine supplements should be taken either cold or at room temperature because the heat can destroy the product.
There is insufficient evidence to support the use of glutamine supplementation in healthy adults or those who are well trained as a mechanism for improving muscularity, strength, power or recovery.
Those involved in endurance-based exercise however may obtain some added value by using glutamine but exactly who glutamine can benefit remains unclear because the results of research thus far are varied and generally inconsistent.