Glutamine Supplements consist of pure L-Glutamine powder or capsules. Glutamine is an amino acid found in muscle tissue. Intense exercise and muscle strain depletes muscle stores of glutamine, which leads to catabolism (Muscle breakdown). Using Glutamine Supplements like Prolab Glutamine or AST Sports Science Micronized L-Glutamine is thought to decrease muscle catabolism which is extremely important when dieting to get lean.