The most abundant amino acid in the muscles is glutamine; muscle tissues possess large amounts of this amino acid in free form. Glutamine is often called brain fuel, as it is easily able to bypass the blood-brain barrier and is important for the metabolic functions in the central nervous system. Glutamine undergoes biochemical conversion into the related amino acid glutamic acid in the brain - both these compounds are therefore vital for brain functioning. Glutamine also tends to bring about an increase in the amount of the neurotransmitter compound called GABA - a vital compound necessary for sustained brain functioning and normal levels of mental performance. The presence of glutamine in the body is helpful in the acid-alkaline base balance in the body. Glutamine is one of the amino acids necessary as a base or is a component building block for many of the proteins involved in the synthesis of nucleic acids - namely RNA and DNA. Glutamine is also essential in the maintenance of a healthy digestive tract and sustains general mental ability in a person.

Nitrogen is released into the general biochemical soup of the body during the metabolic break down process of any amino acid. Nitrogen is a vital nutrient for the human body, however, free nitrogen in the body is converted into ammonia - this compound is very toxic to brain and other tissues if present in excess amounts over any length of time. The conversion of nitrogen into urea occurs in the liver, the urea thus produced is quickly excreted in the urine. Some of the free nitrogen may also bind with glutamic acid and this process results in the synthesis of glutamine. The uniqueness of glutamine is among the amino acids lies in the fact that every single molecule of the amino acid contains not one nitrogen atom but two atoms. Glutamine synthesis thus aids in clearing ammonia rapidly from the tissues - in particular from the brain tissue, and at the same time, this pathway leads to the transfer of the extra nitrogen from one compound to another compound.

Muscle cells and tissue proteins contain the amino acid glutamine in very large amounts, this pool of amino acid is for immediate use as and when required for the biochemical synthesis of skeletal muscle proteins at any time. Glutamine supplements may be beneficial for people on a high protein diet and bodybuilders as the amino acid actively aids in building and maintaining muscle mass. Glutamine can also aid in preventing the form of wasting in the muscles that result’s from prolonged bed rest or that comes about by long term effects of diseases like cancer and full blown AIDS. Wasting in the muscles can result from physical stress and injury - or even trauma induced by surgical procedures, such stresses induce muscle tissues to release large amounts of glutamine into the bloodstream of the person. Stressful times can in fact, lead to the release of more than one third of all the glutamine present in the muscles into the bloodstream. The loss of skeletal muscle mass is thus often a direct result of long term stress or the effect of persistent illness. This loss of skeletal muscle mass can still be prevented if enough glutamine is available in the general circulation.

The treatment of disorders such as arthritis, all sorts of autoimmune diseases, cystic fibrosis, and other intestinal disorders, including peptic ulcers, and some connective tissue diseases like poliomyelitis and scleroderma and tissue damage resulting from radiation treatment for cancer can be carried out using supplemental L-glutamine doses. Mental functioning and general nervous system health is also aided by supplements of L-glutamine. Such supplements have indeed been used in the treatment of a wide range of different problems including many kinds of developmental disabilities, disorders such as epilepsy, physical fatigue, the problem of male impotence, and psychiatric disorders like schizophrenia and age induced senility in old people. Sugar cravings is also decreased by supplements of the L-glutamine, the amino acid also reduces the desire for alcohol and is very helpful in the treatment of alcoholics who are recovering from the long term physical and mental effects of alcohol.

Glutamine is found in different plant and animal food sources - however, cooking destroys it easily. Good plant sources for glutamine include raw spinach and parsley. Glutamine supplements have to be stored in an absolutely dry state or the glutamine powder will quickly degrade into ammonia and pyroglutamic acid over time. Supplemental glutamine in any form must not be consumed by individuals affected by liver cirrhosis, any kind of kidney disorders, problems like Reye's syndrome, or from any sort of physical or metabolic disorder which results in the accumulation of ammonia in the blood in high amounts. Serious damage to the body can ensue in such individuals, if they take supplemental glutamine over any length of time. The various compounds glutamine, glutamic acid (called glutamate at times), the glutathione, wheat gluten, and monosodium glutamate are all different compounds with distinct properties even if they have similar sounding names.

All protein rich foods, like fish, different kinds of meats, plant foods like beans and dairy products tend to be rich in glutamine.

Deficiency of glutamine affects only a very few people and usually for complex reasons, this is partly due to the synthesis of glutamine in the body itself - thus deficiency of glutamine is rare. Deficiencies from low levels of glutamine can however, develop during long periods of fasting, as a result of long term starvation, due to liver cirrhosis, or because of critical illnesses in general. Such deficiencies can also result from weight loss connected to full blown AIDS and cancer.