L-Glutamine
Conditionally essential amino acid that supports gut lining integrity and immune function.
What is L-Glutamine?
Glutamine is the most abundant amino acid in the body and a primary fuel source for intestinal epithelial cells and immune cells. Under normal conditions, the body produces enough glutamine. But during intense training, illness, or physiological stress, demand can exceed supply: making it conditionally essential. It plays a key role in maintaining the intestinal barrier, which prevents gut permeability ("leaky gut").
What does the evidence say?
A 2011 study by Kim and Kim found glutamine supplementation significantly improved gut barrier function markers in critically ill patients. Research in athletes (Calder and Yaqoob, 2012) shows modest immune support effects. The evidence for muscle recovery specifically in trained individuals is weaker than marketing suggests: most people eating adequate protein already have sufficient glutamine.
Good evidence from several studies, but with some limitations in size, duration, or methodology.
Dosage guide
| Effective dose | 5–10g per day |
| Maximum dose | 30g/day (used in clinical settings without significant adverse effects) |
| Timing | Post-training or with meals. |
Best form to buy
L-glutamine powder. Unflavoured mixes easily into protein shakes.
Who benefits most
Men with gut issues (IBS, leaky gut symptoms, frequent illness during high training volume), and those on very low-calorie diets that may compromise gut integrity.
Side effects and safety
Well tolerated at standard doses. Very high doses may affect glutamate-GABA balance in the brain, not relevant at typical supplemental doses.
“If your gut is causing problems, this is a reasonable and cheap thing to try. If you're just looking to improve muscle recovery and your protein intake is adequate, save your money.”