In the body, the amino acid L-glutamine is produced in muscle and is found there in the highest concentrations. It performs numerous functions in metabolism, for example, promoting the formation of glutathione. L-glutamine is used by certain cells in the body, such as muscle cells or the intestinal mucosa, as an energy source. As your energy needs increase, the amount of L-glutamine required also increases. Although the body can produce L-glutamine itself, adequate dietary intake is essential, especially during periods of increased need, such as intense exercise.