L-Glutamine
The most abundant free amino acid in muscle, heavily marketed for recovery and immunity. In healthy, well-fed athletes controlled trials show little to no ergogenic or recovery benefit; genuine value is largely limited to clinical catabolic states such as gut injury or critical illness.
01 Overview
Glutamine is a conditionally essential amino acid central to gut and immune-cell metabolism. This physiology fuelled popular claims that supplementation aids muscle recovery, growth and immune resilience in athletes.
Controlled human trials in healthy, adequately fed athletes have generally not supported those claims: effects on strength, body composition and post-exercise immune function are minimal. The clearer evidence base is clinical, in conditions like severe burns, gut mucosal injury and critical illness, which is a different context from sports performance. Included here to document a widely sold supplement whose athletic evidence is weak.
02 Mechanism
Serves as a primary fuel for enterocytes and immune cells and as a nitrogen donor; supplementation is proposed to support recovery and gut/immune function, but this is not reliably demonstrated in fed, healthy athletes.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Common | 5–10 g/day | Oral | Typical marketed dose; clinical (gut/critical-care) protocols use higher amounts under supervision. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Recovery/immune benefit in athletesPopular recovery and immune claims are largely unsupported in healthy, well-fed athletes. | Little to none | Disputed | |
| Gut mucosal support in clinical catabolismGenuine benefit is limited to clinical states such as gut injury, burns and critical illness, not sport. | Context-specific | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Generally well toleratedWell tolerated in healthy adults at supplement doses; adverse effects are uncommon. | Mild | Typical | Clinical | |
| Gastrointestinal discomfortMild bloating at higher doses. | Mild | Occasional | Observational |