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Gluamine is neither an essential nor a non-essential amino acid. It is a conditionally essential amino acid. This means the body is unable to produce enough glutamine under certain circumstances such as periods of intense exercises, after surgery, infectious disease, and so on.
The body uses about 20 or so amino acids in protein synthesis. Of these, Glutamine is the most abundant, making up about 50% of blood amino acid concentration and about 60% of total amino acids in the body. After BCAAs, Glutamine is the next most important amino acid for anabolism. As a nitrogen and carbon donor, glutamine is an important muscle-building amino acid. Glutamine possesses a unique structure: It contains two nitrogen side chains. This means that it is responsible for about a third of the nitrogen that penetrates the muscle cell. As an anti-catabolic amino acid, glutamine regulates protein synthesis in muscles by preserving muscle cells and boosting post-exercise muscle glycogen. Glutamine's capacity to maintain lean mass and enhance nitrogen retention is also particularly important during periods of low calorie intake.
Glutamine synthesis protects the body and brain from ammonia toxicity. Glutamine can cross the blood-brain barrier. At the brain level, Glutamine is a crucial substrate for the production of excitatory and inhibitory neurotransmitters, glutamate and glutamate and gamma-aminobutyric acid (GABA). Some glutamate is used in the synthesis of Niacin and Glutathione, some as energy, and some as neurotransmitter. Furthermore, the nervous system requires Glutamine as a source of energy. When the brain does not receive enough glucose, it increases glutamine metabolism for energy. This is why glutamine is sometimes referred to as "brain food". Also, glutamine helps prevent hypoglycemia, as it is converted to glucose when blood sugar is low. Glutamine also helps in regulating cellular fluid levels via its dependence on sodium transport.
Glutamine plays a vital role in supporting the immune system via boosting white blood cells, and is important in maintaining the integrity of the gastro-intestinal lining.
In my opinion, therefore, the only problem with glutamine supplementation that could give the erroneous impression that glutamine is worthless, is the fact that only about 20% of regular L-Glutamine consumed ever reaches the blood stream to elicit anti-cataboilic and anabolic effects. This means that 80% of ingested Glutamine is absorbed by the intestines and used for immune-system support. To get around this situation, very large amounts (> 20g) of Glutamine would need to be supplemented daily. Some have even suggested placing the glutamine directly under the tongue and allowing it to dissolve slowly. This way more Glutamine will be absorbed into the blood stream. Alternatively, advanced Gluamine forms and Glutamine precursors can be used. Examples include L-Glutamine-Alpha Ketoglutarate, N-Acetyl-L-Glutamine, N-Alanyl-L-Glutamine, L-Alanine, and Alpha Ketoglutarate. This way, a smaller quantity would be required.
