Optimum Nutrition Glutamine Powder Highlights: Glutamine is the most abundant amino acid in the body, comprising more than 60% of the free amino acid pool in skeletal muscle and greater than 20% of total circulating amino acids. During prolonged, intense exercise, muscle glutamine levels may be depleted, and this can limit protein synthesis.¹ Glutamine Powder is an easy way to supplement your diet. This instantized powder mixes easily and is unflavored for 'stacking' with protein shakes.