Glutamine is the most abundant free amino acid found in the muscles of the body. Because it can readily pass the blood-brain barrier, it is known as brain fuel. In the brain, glutamine is converted into glutamic acid-- which is essential for cerebral function--and vice versa. It also increases the amount of GABA, which is needed to sustain proper brain function and mental activity. It assists in maintaining  the proper acid/alkaline balance in the body, and is the basis of the building blocks for the synthesis for RNA and DNA. It promotes mental ability and the maintenance of healthy digestive tract. 

Glutamine is found in large amounts in the muscles and is readily available when needed for the synthesis of skeletal muscle proteins. Because this amino acid helps to build and maintain muscles, supplemental glutamine is useful for dieters and bodybuilders. More important, it helps to prevent the kind of muscle wasting that can accompany prolonged bed rest or diseases such as cancer and AIDS. This is because stress and injury (including surgical trauma) cause the muscles to release glutamine into the bloodstream. In addition, glutamine helps strengthen the lining of the intestinal tract, so that nutrients are more efficiently absorbed. This is important for wasting diseases such as cancer. 

In fact, during times of stress, as much as one third of the glutamine present in the muscles may be released. As a result, stress/and or illness can lead to the loss of skeletal muscle. If enough glutamine is available, this can be prevented. 

Supplemental L-glutamine can be helpful in the treatment of arthritis, autoimmune disease, fibrosis, intestinal disorders, peptic ulcers, connective tissue disease such as polymyositis and scleroderma and tissue damage due to radiation treatment for cancer. L-glutamine can enhance mental functioning and has been used to treat a range of problems, including developmental disabilities, epilepsy, fatigue, impotence, depression, schizophrenia, and senility. It preserves glutathione in the liver and  protects that organ from the effects of acetaminophen overdose. It enhances antioxidant protection. L-glutamine decreases sugar cravings and the desire for alcohol, and is useful for recovering  alcoholics.