L-Glutamine (glutamine) is the most abundant free amino acid in the body and is an energy substrate for most cells—especially the enterocytes (intestinal epithelial cells) lining the intestines and immune cells. Glutamine is necessary for the maintenance of many metabolic functions. Under situations of stress, physiological demands increase, triggering a need for glutamine supplementation. It is considered a conditionally essential amino acid because, under normal circumstances, the body can manufacture enough to sustain physiological demands. However, under metabolic stress—such as illness/disease, injury, infection, surgery, chemotherapy, prolonged exercise, or environmental stress—glutamine is released from body stores into the bloodstream and transported to tissues in deficit. Increased demands make exogenous glutamine sources (food, supplements) a necessity [1].

Support During and Recovery After Stress States

During stress states, the body’s glutamine requirement exceeds supply, severely reducing both plasma and skeletal muscle pools of free glutamine [2]. Without adequate glutamine to meet the needs of the intestine, immune system, and vital organs, a negative nitrogen balance and catabolism can result [3]. Nitrogen is necessary to repair wounds and keep the vital organs functioning with approximately one-third of this nitrogen coming from glutamine. In fact, it has been recommended that patients preparing for elective surgery ready themselves nutritionally, in part through glutamine supplementation, to optimize recovery [5]. Research also suggests glutamine may help diminish risks associated with conventional therapeutics—such as high-dose chemotherapy and radiation—by supporting mucosal integrity, immune competence, and glutathione biosynthesis [4,6,7].

Intestinal Health and Barrier Function

The greatest amount of glutamine is used by enterocytes. As their preferred fuel source, glutamine is necessary for their maintenance and healthy turnover. Supplementation may therefore enhance mucosal health [1,8]. A healthy intestinal mucosa not only supports optimal nutrient absorption, but it also supports mucosal immune function and provides a barrier between bacteria and their products in the intestines and the bloodstream [1,9,10]. Disruption of intestinal barrier function can lead to decreases in mucosal immune activity and increases in escaping toxins and bacteria, resulting in infections, illness, allergic reactions, skin conditions, and more.

Muscle Tissue Preservation

Of the 20 amino acids required for protein synthesis, glutamine is the most abundant. It makes up 50% of all amino acids in the blood and 60% of those in the body. Not only is glutamine necessary to maintain positive nitrogen balance and protein synthesis, but also it has recently been shown to prevent muscle loss by influencing myostatin levels [11]. Myostatin is a protein that inhibits muscle differentiation and growth and glutamine prevents build-up of this protein [12].  

References

1. Walsh NP, Blannin AK, Robson PJ, et al. Glutamine, exercise and immune function. Links and possible mechanisms. Sports Med. 1998 Sep;26(3):177-91. [PMID: 9802174]
2. Oliveira GP, Dias CM, et al. Understanding the mechanisms of glutamine action in critically ill patients. An Acad Bras Cienc. 2010 Jun;82(2):417-30. [PMID: 20563423]
3. Calder PC, Yaqoob P. Glutamine and the immune system. Amino Acids. 1999;17(3):227-41. [PMID: 10582122]
4. Kuhn KS, Muscaritoli M, Wischmeyer P, et al. Glutamine as indispensable nutrient in oncology: experimental and clinical evidence. Eur J Nutr. 2010 Jun;49(4):197-210. [PMID: 19936817]
5. Awad S, Lobo DN. What's new in perioperative nutritional support? Curr Opin Anaesthesiol. 2011 Mar 30. [Epub ahead of print] [PMID: 21451404]
6. Anderson PM, Schroeder G, Skubitz KM. Oral glutamine reduces the duration and severity of stomatitis after cytotoxic cancer chemotherapy. Cancer. 1998 Oct;83(7):1433-39. [PMID: 9762946]
7. Rocha BR, Gombar FM, Barcellos LM, et al. Glutamine supplementation prevents collagen expression damage in healthy urinary bladder caused by radiotherapy. Nutrition. 2010 Dec 15. [Epub ahead of print] [PMID: 21167680]
8. dos Santos RG, Viana ML, Generoso SV, et al. Glutamine supplementation decreases intestinal permeability and preserves gut mucosa integrity in an experimental mouse model. JPEN J Parenter Enteral Nutr. 2010 JulAug;34(4):408-13. [PMID: 20631386]
9. Nose K, Yang H, Sun X, et al. Glutamine prevents total parenteral nutritionassociated changes to intraepithelial lymphocyte phenotype and function: a potential mechanism for the preservation of epithelial barrier function. J Interferon Cytokine Res. 2010 Feb;30(2):67-80. [PMID: 20028208]
10. Li N, Neu J. Glutamine deprivation alters intestinal tight junctions via a PI3-K/ Akt mediated pathway in Caco-2 cells. J Nutr. 2009 Apr;139(4):710-14. [PMID: 19211824]
11. Bonetto A, Penna F, Minero VG, et al. Glutamine prevents myostatin hyperexpression and protein hypercatabolism induced in C2C12 myotubes by tumor necrosis factor-α. Amino Acids. 2011 Feb;40(2):585-94. [PMID: 20623149]
12. Bonetto A, Penna F, Minero VG, et al. Glutamine prevents myostatin hyperexpression and protein hypercatabolism induced in C2C12 myotubes by tumor necrosis factor-α. Amino Acids. 2011 Feb;40(2):585-94. [PMID: 20623149]