Glutamine has an important structural role, comprising 5-10% of amino acid residues in various proteins. Glutamine is a major vehicle for the transfer of nitrogen between tissues. Maximum growth and proliferation of most cell types occur with adequate glutamine stores. Dependence on glutamine for cellular growth and function has been clearly demonstrated for intestinal mucosal cells and cells of the immune system.(1) Glutamine plays a key part with the branched chain amino acids (BCAA) in muscle energy metabolism and the over training syndrome of athletes. Approximately, 55% of glutamine taken up is oxidized via alpha-ketogluterate and the Krebs cycle to form CO2 and a further 20% is incorporated into citrate, lactate, organic acids, and glucose. Most glutamine is partly metabolized to form alanine and lactate. During fever, surgery, and trauma muscle free glutamine concentrations fall. Adequate circulating glutamine is needed for mucosal healing and muscle protein synthesis; therefore glutamine may be considered �€�conditionally essential.�€� Studies suggest that providing increased oral protein intake can replete muscle glutamine concentrations.(2) The relative mild stress of weight training can result in a significant decline in skeletal muscle free glutamine.(3) Over training is associated with even greater decreases in muscle glutamine and to somewhat lesser extent plasma glutamine concentrations.(4) There is a higher rate of glutamine synthesis and release in skeletal muscle in catabolic or weight loss states. Extensive animal studies have demonstrated that declining glutamine levels are correlated with negative nitrogen balance, decreased rates of protein synthesis and increased protein degradation. Therefore, the provision of glutamine might have anabolic effects leading to improved tissue function. The potential therapeutic use of glutamine as a nutrient in human beings has been investigated in several recent studies. All of these studies compared nitrogen balance and all found that the groups that received glutamine via TPN had greatly improved nitrogen balance. A large body of data in experimental animals and increasing data in human beings indicate that glutamine supplemented nutrition can have significant therapeutic benefit in the management of catabolic disease states. What we have established is that glutamine is an anti-catabolic nutrient and secondly that glutamine should be one of the essential or indispensable amino acids. Glutamine is anti-catabolic because it may spare muscle tissue during stress. This means if youre a natural body builder, subjecting yourself to a certain amount of stress, the body responds by producing cortisol. The cortisol then proceeds to breakdown muscle tissue. This is one of the reasons why natural body builders have a difficult time making muscular gains. So supplementing with glutamine would then impart muscle sparing. In time the muscle that would have been lost is still there and eventually will add up to muscular gains. Another aspect of glutamine would be during the contest phase of bodybuilding. This phase includes the stress of training coupled by the stress of the pre-contest diet i.e. hypocaloric intake. The dieting bodybuilder is similar in comparison to the malnourished or hypermetabolic patient. The main difference is that the bodybuilder is performing heavy resistance type training in order to spare muscle mass. Glutamine is more important to the dieting bodybuilder due to its anti-catabolic and muscle sparing properties. Glutamine supplements during a dieting phase may cause muscle sparing and fullness due to cellular volumizing. The exact amount of glutamine needed by bodybuilders has not been scientifically established. The current data indicates ingesting 5-10 grams per day. It would also make sense to load on glutamine with 20 grams or 4 tsp. divided throughout the day for 5 days then maintain glutamine stores with 5-10 grams per day. Glutamine should not only be considered a conditionally essential amino acid but also a conditionally essential bodybuilding supplement.