In catabolic states of injury and illness, glutamine becomes conditionally-essential (requiring intake from food or supplements). Glutamine is the most abundant naturally occurring, non-essential amino acid in the human body and one of the few amino acids that can directly cross the blood–brain barrier.
[1] Glutamine is a key pharmaconutrient in the body's response to stress and injury. Glutamine exerts its protective effects via multiple mechanisms, including direct protection of cells and tissue from injury, attenuation inflammation, and preservation of metabolic function.
[1]