is the most abundant amino acid (building block of protein) in the bloodstream. It is considered a "conditionally essential amino acid" because it can be manufactured in the body, but under extreme physical stress the demand for glutamine exceeds the body's ability to synthesize it.
Glutamine is primarily produced in the muscles and appears to play an important part in keeping them functioning normally. It's also used by white blood cells and contributes to normal immune-system function. Several types of important immune cells rely on glutamine for energy without it the immune system would be impaired. One of glutamine's most important tasks in the body is to nourish cells that line the intestine and stomach.
L-Glutamine passes freely across the blood-brain barrier. Once in the brain, it's converted to glutamic acid and increases the concentration of GABA (gamma-aminobutyric acid). Both glutamic acid and GABA are essential for proper mental function. Because of its action in the brain, glutamine supplements have been recommended for preventing the deleterious effects of alcohol on the brain and for reducing different kind of cravings. Some sources describe glutamine as a "brain fuel" capable of stimulating mental alertness and clear thinking.
Adequate amounts of glutamine are generally obtained through diet alone because the body is also able to make glutamine on its own. Certain medical conditions, including injuries, surgery, infections, and prolonged stress, can deplete glutamine levels, however. In these cases, glutamine supplementation may be helpful. L-Glutamine has also been used for treating weight loss, insomnia, depression, and anxiety.