Supplements: Glutamine
Antonio & Street (1999, PMID 10574520): 6 weeks of 0.9g/kg/day glutamine in resistance-trained athletes produced no significant effect on strength, lean mass, or muscle glycogen compared to placebo.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Evidence Tier | 4 | tier | Insufficient — for athletic performance; Tier 1 for critical illness/surgical contexts |
| Studied Athletic Dose | 5 | g/day | Standard supplement dose; no performance benefit found at this or higher doses |
| High Dose Studied | 0.9 | g/kg/day | Antonio & Street 1999 — highest dose studied in athletes; still no effect on muscle |
| Muscle Glutamine Content | 60 | % of free amino acids | Glutamine comprises ~60% of the free amino acid pool in skeletal muscle |
| Critical Illness Depletion | 50 | % reduction | Plasma glutamine falls ~50% in ICU patients; supplementation is evidence-based here |
| Body Production | ~80 | g/day | Healthy adults synthesize approximately 80g glutamine/day endogenously |
Glutamine sits at an interesting intersection: it has excellent evidence in clinical medicine and essentially zero evidence for athletic performance. The supplement industry has borrowed credibility from the hospital literature and misapplied it to healthy athletes.
The Physiology
Glutamine is the most abundant free amino acid in skeletal muscle, comprising approximately 60% of the free amino acid pool. The body synthesizes roughly 80g per day endogenously — far more than any supplement dose provides. It is classified as conditionally essential: non-essential under normal conditions, but essential when biosynthetic capacity is overwhelmed by illness, injury, or severe catabolic stress.
Clinical Evidence (Real)
In the ICU, plasma glutamine falls approximately 50% during critical illness. Tissues with high turnover — gut epithelium, immune cells — preferentially consume glutamine, and endogenous synthesis cannot keep pace. Wischmeyer’s work (PMID 18301272) demonstrated meaningful improvements in outcomes with IV and enteral glutamine supplementation in surgical and ICU populations. This is legitimate medicine.
Athletic Evidence (Absent)
| Claim | Evidence Context | Athletic Evidence | Verdict | Who It Actually Helps |
|---|---|---|---|---|
| Muscle mass increase | Clinical: no relevance | Zero (Antonio 1999) | No benefit | Nobody with adequate protein |
| Muscle glycogen resynthesis | Plausible mechanism | No effect in trained athletes | No benefit | — |
| Immune function boost | Low glutamine in overtraining | Supplementation didn’t fix it | No benefit | Reduce training load instead |
| Gut health (healthy) | Real in IBD, Crohn’s | No evidence in healthy athletes | No benefit | GI disease patients |
| Gut health (leaky gut) | Real in critical illness | Not applicable to athletes | No benefit | ICU / burn patients |
| Recovery / DOMS | Popular marketing claim | No RCT support | No benefit | — |
| Anti-catabolism | Plausible from muscle pool | Not demonstrated in humans | No benefit | — |
The Overtraining Confound
Castell et al. (1996, 1997, PMID 9263261) observed lower plasma glutamine in athletes with signs of overreaching and higher rates of upper respiratory infection. This correlation was real. The error was concluding that glutamine supplementation would correct it. Subsequent work showed that plasma glutamine reflects training load — when you reduce overtraining, plasma glutamine normalizes. Supplementation does not fix the underlying cause and does not improve infection rates.
Practical Conclusion
Save the glutamine budget. A healthy athlete producing 80g/day endogenously does not have a glutamine deficit. The 5–10g supplement doses sold commercially represent a fraction of daily endogenous production. If you are eating adequate protein (≥1.6g/kg/day), you are already consuming substantial glutamine — whey protein is approximately 4–5% glutamine by weight.
Glutamine is a genuinely important molecule. It is simply not one you need to supplement when you are healthy and eating enough protein.
Related Pages
Sources
- Antonio J, Street C. Glutamine: a potentially useful supplement for athletes. Can J Appl Physiol. 1999;24(1):1-14. PMID 10574520
- Wischmeyer PE. Glutamine: role in critical illness and ongoing clinical trials. Curr Opin Gastroenterol. 2008;24(2):190-197. PMID 18301272
- Castell LM, Newsholme EA. The effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise. Nutrition. 1997;13(7-8):738-742. PMID 9263261
Frequently Asked Questions
Does glutamine improve muscle recovery after exercise?
No consistent evidence supports this in healthy athletes consuming adequate protein. Antonio & Street (1999, PMID 10574520) found zero effect on strength or lean mass after 6 weeks at 0.9g/kg/day — a dose far exceeding standard supplement servings. The body produces approximately 80g of glutamine per day endogenously, which is more than sufficient for healthy athletes.
Does glutamine boost immune function in athletes?
Plasma glutamine is lower in overtrained or overreached athletes (Castell & Newsholme 1997), which led to the hypothesis that supplementation would reduce illness. However, follow-up research showed that supplementing glutamine in athletes did not meaningfully improve infection rates or immune markers. Low plasma glutamine in overreaching reflects training load, not a dietary deficiency correctable with supplements.
Who actually benefits from glutamine supplementation?
Critically ill patients in the ICU, post-surgical patients, severe burn victims, and individuals with inflammatory bowel disease. In these populations, glutamine is genuinely depleted beyond the body's ability to synthesize enough, and IV or oral supplementation improves outcomes (Wischmeyer 2008, PMID 18301272). Healthy athletes are not in this category.
Does glutamine improve gut health?
In gastrointestinal disease — Crohn's disease, ulcerative colitis, leaky gut in critical illness — yes, there is evidence for gut barrier support. In healthy athletes with normal gut function, there is no evidence that supplemental glutamine improves gut integrity, permeability, or microbiome composition beyond what a high-protein diet already provides.
Is glutamine safe to take as a supplement?
Yes, it is safe. Standard doses of 5–10g/day have no documented adverse effects. The issue is not safety but efficacy: spending money on glutamine for performance goals provides no benefit beyond what adequate dietary protein already achieves.