Glutamine is one of the 20 naturally occurring amino acids in dietary protein, specifically it is a conditionally essential amino acid (being elevated to essential during periods of disease and muscle wasting typical of physical trauma). It is sold as an isolated amino acids as well as being found in high levels in dietary meats and eggs. It is found in very high levels in both whey and casein protein. Glutamine is a very effective intestinal and immune system health compound, as these cells use glutamine as the preferred fuel source rather than glucose.
Glutamine is generally touted as a muscle builder, but has not been proven to enhance muscle building in healthy individuals; only those suffering from physical trauma such as burns or muscular wounds (knife wounds) or in disease states in which muscle wasting occurs, such as AIDS. In these individuals, however, glutamine is effective at building muscle and alleviating a decrease in muscle mass typical of the ailment.
Supplementation of L-glutamine tends to be dosed at 5g or above, with higher doses being advised against due to excessive ammonia in serum. The lowest dose found to increase ammonia in serum has been 0.75g/kg, or approximately 51g for a 150lb individual.
Due to the relative inefficacy of glutamine supplementation for increasing muscle mass, the optimal dosage is not known. The above recommended doses are sufficient for intestinal health reasons and for attenuating a possible relative glutamine deficiency (seen in instances of low protein intake or veganism).