Glutamine and Gut: Permeability, Irritable Bowel, What Research Shows

Because the cells that line the intestine, enterocytes, use glutamine as their primary fuel, before glucose. It is the most abundant amino acid in blood and muscles, and the body produces it itself; but in situations of metabolic stress, infection, surgery, prolonged effort, demand can exceed production, making it a conditionally essential amino acid. It is on this basis that glutamine has been studied for intestinal barrier function.

Not in a general way, and it's a 2024 meta-analysis that says so. Published in Amino Acids, it combined ten randomized trials versus placebo, from 1998 to 2014, 352 participants, all with various conditions, and measured permeability before and after oral glutamine. Overall, no significant effect. In subgroup analysis, a significant reduction in permeability at doses above 30 g daily for less than two weeks. The authors' conclusion: glutamine acts on permeability at high dose and over short duration, and further trials are needed according to doses and populations.

It is the most striking trial on glutamine and the intestine. Published in Gut In 2019 by Tulane University, it randomized adults who developed diarrhea-predominant irritable bowel syndrome following an intestinal infection, with increased intestinal permeability measured by the lactulose-mannitol test. Eight weeks at 5 g of glutamine three times daily or placebo. The primary endpoint, a decrease of at least 50 points in the severity score, was achieved in 79.6% of patients on glutamine versus 5.8% on placebo. Stool frequency decreased from 5.4 to 2.9 per day, permeability normalized, and no serious adverse effects were observed. The authors call for large trials to confirm.

No, and that's the essential point. The trial in Gut focuses on a very specific population: irritable bowel syndrome that appeared after an infection, with measured hyperpermeability. It does not cover irritable bowel syndrome in general, nor bloating, nor leaky gut as discussed on the internet. The meta-analysis also shows that in diverse patient populations, the average effect on permeability is null at usual doses. Glutamine therefore has a documented, narrow and clear indication, and not general efficacy for the intestine.

Intestinal permeability is a measurable parameter: two sugars, lactulose and mannitol, are ingested and their ratio is measured in urine. A high ratio indicates a more permeable barrier, which is observed in certain inflammatory diseases, celiac disease, after certain infections or extreme exertion. Conversely, leaky gut syndrome as an autonomous diagnosis, cause of fatigue, joint pain or allergies, is not a recognized medical entity. Trials on glutamine focus on the measured parameter, not the syndrome.

Not according to the reference review. Published in the Journal of Nutrition by Michael Gleeson, from Loughborough University, it recalls that prolonged exercise decreases plasma glutamine, but that supplementation trials, although they maintain this level, do not prevent post-exercise immune changes, because the decrease is not sufficient to limit lymphocyte proliferation. It notes that 20 to 30 g in a single dose and 28 g per day for 14 days were well tolerated, and concludes that the reasons given for supplementation, immunity, glycogen, anticatabolic effect, received little support from well-controlled trials in healthy and well-nourished adults.

In healthy adults, at trial doses, yes: up to 30 g per day with no notable adverse effects, and no serious effects in the Gut trial at 15 g per day for eight weeks. However, there is a clear limit, set by the REDOXS trial published in the New England Journal of Medicine : in 1,223 intensive care patients with multiorgan failure, high-dose glutamine given intravenously and enterally was associated with increased hospital and six-month mortality. This is a context unrelated to a dietary supplement in a healthy person, but it sets the rule: in case of renal or hepatic insufficiency, serious illness or hospitalization, glutamine should be decided with a doctor, never on your own.

The Gut trial used 5 g three times daily, or 15 g, for eight weeks. The meta-analysis on permeability finds an effect only above 30 g per day for less than two weeks, in patients. The amounts that showed something are therefore in the range of 15 to 30 g per day, in multiple doses, and over weeks. A powder is dosed with a 5 g measure, which allows adjustment. And any persistent abdominal pain, any bleeding, any weight loss or diarrhea that persists should be discussed with a doctor before any supplement.

That glutamine is the fuel for intestinal cells, and that's the basis of its study. That a meta-analysis finds no general effect on permeability, except at high doses. That a Gut trial shows a clear effect, 79.6 versus 5.8% responders, in very specific patients: post-infectious irritable bowel syndrome with measured hyperpermeability. That leaky gut as a syndrome is not a recognized diagnosis. That athlete immunity has no solid evidence. And that glutamine is safe in healthy adults, but should be decided with a doctor in case of serious illness.