Healthy Origins American-made l-glutamine is an amino acid produced by the body to serve as a building block for proteins. It also helps supply fuel to the immune cells inside your GI tract. L-glutamine is the most abundant amino acid found in your blood and muscle tissue. However, during times of stress or rigorous exercise, your natural levels of l-glutamine may be reduced. For this reason, many athletes choose to add supplemental l-glutamine to their diet and exercise regimen.