L-glutamine — evidence review

• Gut health and immune support at **5 milligrams BID** (10 mg/day).
• Fewer everyday respiratory infections / “I don’t get sick.”
• Faster muscle recovery / less DOMS after lifting or eccentric work.
• More muscle mass or strength from training.
• Faster muscle glycogen refill after hard sessions.
• Better gut barrier / less “leakiness” around hard training or heat.
• General immune support in healthy people.
• Lower 28-day or hospital mortality in ventilated multi-organ-failure patients.
• Fewer ICU-acquired infections.
• Faster discharge alive after severe burns.

**5 mg twice daily** is an unresolved printed figure with **no plausible evidence base**. It is not a studied dose, not a food-equivalent dose, and not a rounding of 5 g. Confidence for any benefit at 5 mg: **unsupported**. **Gram-dose oral L-glutamine (5–30 g/day)** is a real intervention with a split file. The only **approved, outcome-level** win is **Endari 10–30 g/day in sickle cell disease** (one Emmaus Phase 3: median crises 3 vs 4; ACS 8.6% vs 23.1%). **Post-infectious IBS-D with proven hyperpermeability** has one dramatic 15 g/day RCT (Zhou) plus a smaller 15 g add-on-to-low-FODMAP trial (Rastgoo); confidence **moderate for that narrow phenotype, weak for generic IBS or “leaky gut.”** Exercise heat-run studies move a **permeability surrogate** at 0.25–0.9 g/kg FFM and do **not** move symptoms. Small eccentric-exercise RCTs (0.3 g/kg) show **modestly less soreness and slightly better torque recovery**; they do not build muscle (Candow 45 g/day, 6 weeks, null) and do not speed muscle glycogen when carbohydrate is adequate (van Hall). Daily 5 g for “immune insurance” rests on a 1996 self-report and is **contradicted** by immune-cell RCTs and the 2019 athlete meta-analysis.