L-glutamine (free amino acid)

L-glutamine is heavily marketed on iHerb and Amazon as a detox aid, leaky-gut repair and immune support in healthy adults. EFSA rejected the proposed health claims for glutamine: in 2009 for immune function and intestinal-barrier integrity (leaky gut), and in 2011 for muscle mass; the submitted data did not establish a cause-and-effect relationship. There are no high-quality RCTs on leaky gut in healthy people, and medicine does not use the concept of supplement-driven detox. If a friend or shop offers glutamine under these claims, discuss the request with a gastroenterologist or dietitian and consider a second opinion.

L-glutamine is central to the «leaky gut» marketing concept actively pushed by integrative clinics and functional-medicine influencers. The concept: stress, antibiotics, and gluten «open» the gut wall, large molecules enter blood, autoimmune disease, allergy, and chronic inflammation follow, and L-glutamine «heals» epithelial tight junctions. Academic gastroenterology does not accept «leaky gut» as a clinical syndrome: AGA, BSG, and the Spanish SEPD do not include leaky gut in their guidelines. Increased small-bowel permeability is a physiological adaptation seen in many states (coeliac disease, Crohn's, exercise, NSAIDs, infectious gastroenteritis) without clear causality for systemic disease. The Benjamin trial (Gut 2018) in 106 patients with post-infectious diarrhoeal IBS reported symptom improvement in 79% on L-glutamine 5 g three times daily for 8 weeks versus 6% on placebo – an impressive single-centre result not reproduced in larger RCTs. NICE CG61 for IBS recommends low-FODMAP diet, psychological support, and when needed – mebeverine, loperamide, SSRIs and antidepressants; glutamine is not in the guideline. If glutamine was bought «for leaky gut», consider seeking a second opinion – persistent GI symptoms warrant gastroenterology assessment to rule out coeliac disease, SIBO, inflammatory bowel disease, and eosinophilic oesophagitis.

L-glutamine has been marketed to bodybuilders for years as a «post-workout recovery agent» and «muscle catabolism shield». The idea rested on falling plasma glutamine after prolonged exercise and a theoretical immune protection against colds in athletes. Real data in healthy trainees are disappointing. Large meta-analyses and reviews by the American College of Sports Medicine, Australian Institute of Sport, and the IOC consensus statement on dietary supplements 2018 place L-glutamine in the «non-effective» or «unclear evidence» category: muscle hypertrophy, strength, VO2max, and upper respiratory infection rates in athletes do not change. Strength recovery and reduced muscle soreness after eccentric exercise come from adequate protein (1.6-2.0 g/kg/day for trainees), post-exercise carbohydrate, and 8-9 hours of sleep, not from a packet of glutamine. In critically ill patients (burns, polytrauma, ICU ventilation), parenteral glutamine was tested in large RCTs (REDOXS, Heyland 2013, NEJM): adding glutamine to standard parenteral nutrition increased hospital mortality in severely ill patients with renal failure. This is not a supplement indication – ICU glutamine is prescribed by intensive care.

L-glutamine is a free amino acid sold as a superfood and adaptogen, with claims around post-exercise recovery, immune support, and gut "protection" in healthy people. For this use the benefit is unproven: there are no good-quality human trials showing such an effect in people without a deficiency or serious underlying illness. A normal diet already supplies enough glutamine, so taking it as a superfood adds nothing to your food. The substance itself is well tolerated at these amounts. If you have a specific goal (recovery, digestion, immunity), rely on an approach with proven benefit and do not use it in place of a treatment that works.