Glutamine for Athletes: What 30 Years of Research Actually Shows

L-glutamine is the most abundant amino acid in your bloodstream and skeletal muscle — about 60% of the free amino acid pool. The supplement industry has marketed it for hypertrophy, recovery, and immunity. The peer-reviewed evidence is more nuanced.

What Glutamine Actually Does

Glutamine fuels rapidly dividing cells — gut enterocytes, lymphocytes, kidney cells. During heavy training, illness, or caloric restriction, glutamine demand can outstrip what the body produces, dropping plasma levels by 20–50%.

For Muscle Growth: Underwhelming

A 2001 trial gave resistance-trained men 0.9 g/kg of glutamine daily for 6 weeks. No difference vs placebo in strength, lean mass, or muscle protein degradation. Subsequent trials echo this. If you eat enough protein, glutamine adds nothing to hypertrophy.

For Endurance & Immunity: Mixed but Promising

Heavy endurance training causes a transient post-exercise immune dip ("open window") linked to dropping plasma glutamine. Studies in marathoners and military recruits show 5 g pre- and post-exercise reduced self-reported URTI (upper respiratory tract infection) rates.

For Gut Health: The Strongest Case

Endurance athletes commonly develop exercise-induced gut permeability ("leaky gut"). 5–10 g of glutamine has been shown to reduce intestinal permeability markers and GI symptoms during prolonged exercise in the heat.

The Bottom Line

Don't buy glutamine for muscle gain. Consider it if you're an endurance athlete in a heavy block, dealing with GI symptoms, or repeatedly sick mid-season. 5 g, once or twice daily, with or without food.