Glutamine Supplements consist of pure l-glutamine powder or capsules. Glutamine is an amino acid found in abundant amounts in muscle tissue. Heavy exercise depletes muscle stores of glutamine, which leads to catabolism (muscle wasting). Using Glutamine Supplements, like AST GL3 Glutamine therefore is thought to decrease catabolism - particularly important when dieting to get lean. Other popular L-glutamine supplements include USN and Reflex L-Glutamine.