What Is L-Glutamine L-Glutamine is a nonessential amino acid that plays an important role in metabolic function. It is used by the body to fuel the cells and is the most common amino acid found in the human body. L-Glutamine Benefits Often taken as part of a preworkout regimen, L-Glutamine is most commonly used by athletes and bodybuilders to help boost exercise endurance and to aid in recovery. L-Glutamine may also supports immune function, contribute to healthy metabolic function, and benefit gut and digestive health.*