Glutamine (Gln), also known as L-glutamine is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon).  Amino acids are organic compounds that contain amino (‚ÄìNH2) and carboxyl (‚ÄìCOOH) functional groups, along with a side chain (R group) specific to each amino acid. Structurally, glutamine is similar to the amino acid glutamic acid. However, instead of having a terminal carboxylic acid, it has an amide. Glutamine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Glutamine is found in all organisms ranging from bacteria to plants to animals.  It is classified as an aliphatic, polar amino acid.  In humans glutamine is considered a non-essential amino acid. Enzymatically, glutamine is formed by replacing a side-chain hydroxyl of glutamic acid with an amine functional group. More specifically, glutamine is synthesized by the enzyme glutamine synthetase from glutamate and ammonia. The most relevant glutamine-producing tissue are skeletal muscles, accounting for about 90% of all glutamine synthesized. Glutamine is also released, in small amounts, by the lungs and brain. In human blood, glutamine is the most abundant free amino acid. Dietary sources of glutamine include protein-rich foods such as beef, chicken, fish, dairy products, eggs, beans, beets, cabbage, spinach, carrots, parsley, vegetable juices, wheat, papaya, Brussels sprouts, celery and kale. Glutamine is one of the few amino acids that can directly cross the blood‚Äìbrain barrier. Glutamine is often used as a supplement in weightlifting, bodybuilding, endurance and other sports, as well as by those who suffer from muscular cramps or pain, particularly elderly people. In 2017, the U.S. Food and Drug Administration (FDA) approved L-glutamine oral powder, marketed as Endari, to reduce severe complications of sickle cell disease in people aged five years and older with the disorder. Subjects who were treated with L-glutamine oral powder experienced fewer hospital visits for pain treated with a parenterally administered narcotic or ketorolac. The main use of glutamine within the diet of either group is as a means of replenishing the body's stores of amino acids that have been used during exercise or everyday activities. Studies which have looked into problems with excessive consumption of glutamine thus far have proved inconclusive. However, normal supplementation is healthy mainly because glutamine is supposed to be supplemented after prolonged periods of exercise (for example, a workout or exercise in which amino acids are required for use) and replenishes amino acid stores. This is one of the main reasons glutamine is recommended during fasting or for people who suffer from physical trauma, immune deficiencies, or cancer. There is a significant body of evidence that links glutamine-enriched diets with positive intestinal effects. These include maintenance of gut barrier function, aiding intestinal cell proliferation and differentiation, as well as generally reducing septic morbidity and the symptoms of Irritable Bowel Syndrome (IBS). The reason for such "cleansing" properties is thought to stem from the fact that the intestinal extraction rate of glutamine is higher than that for other amino acids, and is therefore thought to be the most viable option when attempting to alleviate conditions relating to the gastrointestinal tract. These conditions were discovered after comparing plasma concentration within the gut between glutamine-enriched and non glutamine-enriched diets. However, even though glutamine is thought to have "cleansing" properties and effects, it is unknown to what extent glutamine has clinical benefits, due to the varied concentrations of glutamine in varieties of food. It is also known that glutamine has positive effects in reducing healing time after operations. Hospital waiting times after abdominal surgery are reduced by providing parenteral nutrition regimens containing amounts of glutamine to patients. Clinical trials have revealed that patients on supplementation regimes containing glutamine have improved nitrogen balances, generation of cysteinyl-leukotrienes from polymorphonuclear neutrophil granulocytes and improved lymphocyte recovery and intestinal permeability (in postoperative patients) - in comparison to those who had no glutamine within their dietary regime; all without any side-effects.