L-glutamine
Conditionally essential amino acid with RCT signal for diarrhoea-predominant IBS and exercise recovery.
Why
L-glutamine is the most abundant free amino acid in plasma and the preferred fuel for rapidly-dividing cells, including small-intestinal enterocytes and immune lymphocytes. The Zhou 2019 RCT in post-infectious diarrhoea-predominant IBS reported significant reduction in IBS symptom severity score at 5 g three times daily. Smaller bodies support use in ICU patients (reduced infectious complications, mostly historical) and as adjunct in cancer-treatment-related mucositis. Effect in healthy athletes is small.
How it works
Primary metabolic fuel for enterocytes, supports tight-junction integrity and mucosal barrier function. Substrate for glutathione synthesis. Anaplerotic in the TCA cycle during catabolic states (sepsis, burns, intensive training).
Expected onset · IBS-D effects over 4–8 weeks; mucosal repair effects over 2–4 weeks
How to take
Dosage
IBS-D: 5 g three times daily for 8 weeks. General gut-support: 5–10 g/day. Exercise recovery: 0.1 g/kg/day. ICU dosing is clinical context only.
Timing
Between meals; powder dissolved in water
On the label
'L-glutamine' powder or capsules with stated grams. Pharmaceutical-grade is preferred for therapeutic doses.
Ideal for
Adults with post-infectious IBS-D, suspected increased intestinal permeability, or in recovery from intense training or catabolic illness (under supervision).
Safety
Evidence
Zhou 2019 Gut RCT (n=106 post-infectious IBS-D): glutamine 15 g/day for 8 weeks reduced IBS-SSS by ≥50 points in 80% of participants vs 6% on placebo, large effect for this difficult phenotype. REDOXS 2014 raised a specific harm signal in critically ill multi-organ-failure patients, shapes the avoidance in advanced ICU contexts.
- Zhou et al., Gut 2019, randomised placebo-controlled trial of dietary glutamine supplements for postinfectious IBS
- Cruzat et al., Nutrients 2018, glutamine: metabolism and immune function, supplementation and clinical translation
- van Zanten et al., Crit Care Med 2014, REDOXS trial: high-dose glutamine and antioxidants in critically ill patients (RCT), null/harm signal in this population
Where to get it
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