L-Glutamine · supplement
Evidence tier: weak
The primary fuel for gut lining cells, foundational support for leaky gut and gut barrier repair.
Glutamine is the preferred fuel of the enterocytes that line the gut, and in cell and animal models it supports the tight junction proteins that hold the intestinal barrier closed. That is the entire rationale for the leaky gut supplement. It should be treated as a laboratory hypothesis rather than an established human effect, because the human meta analysis of the precise endpoint the mechanism predicts, intestinal permeability, found no effect at all. A mechanism that fails its own predicted outcome in people is not a mechanism you can sell.
Weak for the consumer gut supplement, and that grade sits beside a genuine licensed drug approval that does not transfer to it. Credit first what is real: prescription L-glutamine, sold as Endari, was approved by the FDA in 2017 to reduce the acute complications of sickle cell disease in adults and children aged 5 and over, on the strength of a 230 patient randomised trial published in the New England Journal of Medicine (PMID 30021096) in which the median number of pain crises over 48 weeks was lower on L-glutamine than on placebo. That is a real, replicated, licensed indication for a genetic blood disorder at a prescription dose of 5 to 15 g twice daily. It says nothing about a 5 g scoop taken for gut health, and the two must never be joined in a sentence. Now the consumer claim. The mechanism the whole leaky gut story rests on is that glutamine tightens the intestinal barrier, and the human meta analysis of exactly that endpoint came back NULL: across 10 randomised trials and 352 participants, glutamine supplementation did not significantly affect intestinal permeability (WMD -0.00, 95% CI -0.04 to 0.03, PMID 39397201). The one striking positive, a trial in post infectious diarrhoea predominant IBS reporting 79.6 percent responders against 5.8 percent on placebo (PMID 30108163), is a single centre result with an effect size implausible for any gastrointestinal intervention, in a narrow population with documented hyperpermeability after a confirmed enteric infection, and its own authors call for large trials to validate the findings. It has not been replicated. Glutamine does reduce severe oral mucositis in people receiving chemotherapy and radiotherapy (RR 0.53, 95% CI 0.32 to 0.88, PMID 33598734), but that is an oncology supportive care setting. Post surgical recovery evidence is thin and mostly intravenous. NIH LiverTox assigns L-glutamine likelihood score E, an unlikely cause of liver injury.
Consumer supplements typically supply about 5 g daily; an IBS trial used 5 g three times daily. Note that the only permeability signal appeared above 30 g daily, roughly six times a typical consumer dose, and high dose glutamine is the region where harm has actually been observed, with the REDOXS trial in 1,223 ventilated intensive care patients finding INCREASED mortality on high dose glutamine. The prescription drug Endari is dosed separately by body weight at 5 to 15 g twice daily.
5 to 15 g daily in divided doses, on an empty stomach. Powder mixes easily in water.
Caution in liver/kidney disease and in cancers that may use glutamine. Otherwise very safe.
Pregnancy: caution
Breastfeeding: caution
Active compounds: L-glutamine
Remedies using L-Glutamine · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.