ʟ-Glutamine is the most abundant amino acid in the human body. Glutamine is metabolized in the small intestine and serves as an important fuel source for intestinal mucosa. Glutamine plays an important protective role in the intestinal tract, and is crucial for patients with increased permeability of the intestinal system, which can be seen in patients with inflammatory bowel diseases including, Crohn’s disease or ulcerative colitis, as well as in irritable bowel syndrome and allergies. This amino acid plays an important role in nutrient metabolism, the immune system, protein turnover, and acid-base balance. With infection, severe burns, cancers, and some other pathologies, both intracellular and extracellular concentrations of glutamine are markedly reduced. This leads us to believe that glutamine supplementation may play an important role in the body’s ability to recover from illness. Glutamine has also been studied for use in patients after gastric surgery and may act as a motility-recovery agent after gastrectomy. Patients receiving treatment for cancer often experience malnutrition and cachexia, which may be improved with glutamine supplementation.