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 Zhou and Verne 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.

ICD-10: K58.8 · ICD-11: DD91.0Z

L-glutamine has been tried as an adjunct nutrient in short bowel syndrome. Its stand-alone benefit has not been shown: in combination protocols the effect is attributed to growth hormone (Byrne 2005), and the only pure-glutamine RCT (Scolapio 2001) did not improve outcomes over placebo. ESPEN classes glutamine as conditionally essential when the pool is depleted but does not recommend it as routine short-bowel therapy; teduglutide is preferred. Glutamine itself is harmless; it should not replace proven therapy.

ICD-10: K91.2 · ICD-11: DA96.04

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 sometimes added to ICU nutrition to support critically ill patients. The REDOXS trial (NEJM, 2013) found the opposite: early high-dose glutamine given intravenously and enterally to patients with multi-organ failure raised in-hospital and 6-month mortality. The MetaPlus trial (JAMA, 2014) added a further harm signal in the medical ICU subgroup. The ESPEN ICU nutrition guideline advises against parenteral glutamine in patients with haemodynamic instability and multi-organ failure, reserving it only for selected groups such as major burns and severe trauma. For critical illness with organ failure, L-glutamine is not recommended.

ICD-10: R65.1 · ICD-11: MG4A