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Limited evidenceGut health

L-Glutamine

Glutamine is genuinely conditionally essential in severe catabolic illness, but in healthy people it is one of the most oversold supplements on the market. It does not build muscle, does not reliably prevent post-exercise infections, and the gut-health claims rest on thin human evidence.

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What the science says

  • Muscle growth and exercise performance Limited evidence

    Gleeson's review of dosing and efficacy concluded that glutamine supplementation does not improve muscle mass, strength or exercise performance in healthy trained people. Skeletal muscle synthesises large amounts of glutamine endogenously, and plasma levels in healthy athletes are rarely low enough for supplementation to matter.

  • Preventing post-exercise immune suppression and infections Limited evidence

    The hypothesis that heavy training depletes glutamine and causes the post-exercise "open window" was tested repeatedly and largely failed: Gleeson found glutamine supplementation restored plasma levels but did not prevent post-exercise immune impairment or reduce infection rates in most controlled trials.

  • Clinical benefit in critical illness, burns and surgery Moderate evidence

    McRae's 2017 umbrella review of meta-analyses found glutamine supplementation associated with reduced infection rates and shorter hospital stay in some surgical and burn populations. Findings are inconsistent across analyses, and the large REDOXS trial found increased mortality with high-dose glutamine in critically ill patients with multi-organ failure — so this is a supervised clinical intervention, not a self-care one.

  • Intestinal permeability and "leaky gut" Limited evidence

    Glutamine is the preferred fuel of enterocytes, and small trials suggest it may reduce exercise- or illness-induced increases in intestinal permeability. Human data are few, small and short, and there is no good evidence that healthy people with normal gut barriers benefit.

Dosage & safety

Studied doseExercise and gut studies typically use 5-10 g/day; intestinal permeability protocols have used up to 0.9 g/kg/day short term. Clinical enteral and parenteral protocols use 0.3-0.5 g/kg/day under medical supervision. Doses in the 5 g range are what most consumer products supply.
SafetyWell tolerated in healthy adults at 5-15 g/day; higher doses can cause GI upset. Critically important caveat: high-dose glutamine increased mortality in critically ill patients with renal and multi-organ failure in the REDOXS trial, so it should not be self-administered in serious illness. Avoid in significant liver disease or hepatic encephalopathy (ammonia load) and in urea cycle disorders. Use caution in people with a history of seizures or cancer, where evidence is unsettled. Not banned in sport.

How to take it

TimingTiming does not matter; split larger amounts across the day.
With food?With or without food; higher single doses are better tolerated with a meal.
Worth knowingGlutamine degrades in heat and acid, so mix it into cool water rather than hot coffee or juice.

Frequently asked questions

Does glutamine help build muscle?

No — the evidence is limited. Reviews conclude L-glutamine does not improve muscle mass, strength or exercise performance in healthy trained people, whose muscles already make plenty of glutamine.

Does glutamine boost immunity after hard training?

Not in most controlled trials — the evidence is limited. L-glutamine restored plasma glutamine levels but did not prevent post-exercise immune impairment or reduce infections.

Does L-glutamine help leaky gut?

The evidence is limited: small, short trials suggest glutamine may reduce exercise- or illness-induced gut permeability, but there is no good evidence that healthy people with normal gut barriers benefit.

Is glutamine safe to take?

L-glutamine is well tolerated at 5–15 g/day in healthy adults. Do not self-administer it in serious illness, since high-dose glutamine increased mortality in critically ill patients in the REDOXS trial, and avoid it in significant liver disease.

Scientific references

Where to buy

Doctor's Best, Pure L-Glutamine Powder, 10.6 oz (300 g)

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