Evidence Level
Glutamine is one of the most popular but also most overhyped supplements in sports nutrition. For muscle growth, evidence is clear: glutamine does not enhance muscle protein synthesis or strength gains in well-fed individuals consuming adequate protein (Candow et al., 2001). However, its role in immune and gut health is legitimate. Intense prolonged exercise depletes plasma glutamine by 10-30%, potentially creating an "open window" of immune vulnerability. Castell et al. (1996) showed supplementation reduced post-exercise infections. For gut health, glutamine is genuinely useful as the primary fuel for enterocytes. The practical recommendation: skip glutamine for muscle building (get enough protein instead), but consider it during heavy endurance training blocks or if experiencing exercise-induced GI issues.