Know2eat

L-glutamine

Amino Acids & Proteins

What l-glutamine may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedDigestive comfortLimited evidence· 3 sources

Then, in order

About L-glutamine

The most abundant free amino acid in blood and muscle, and the preferred fuel of intestinal epithelial cells and lymphocytes. It is non-essential under normal conditions but is described as conditionally essential during severe illness or injury.

Glutamine is sold for two very different purposes and the evidence differs sharply between them. For immunity and muscle in healthy people it is essentially null: plasma glutamine falls after prolonged exercise, supplementing restores it, and trials show no consistent effect on infection rates, muscle mass or performance. For the gut the picture is more interesting — a single-centre randomised trial in post-infectious irritable bowel syndrome with diarrhoea reported a striking reduction in symptoms with 5 g three times daily, and glutamine has an approved pharmaceutical use in sickle cell disease. One striking single-centre trial is a reason to run another trial, not a finding.

Sold as
Powder, Capsule, Clinical nutrition formulations, Prescription oral powder
Standardised to
Grams of free L-glutamine; it is unstable in solution and degrades on standing — a product without this marker may not resemble what was studied.
Also known as
Glutamine, L-glutamine powder

Regulation: Sold as a dietary supplement with no pre-market efficacy review, and separately approved by the FDA as a prescription oral powder to reduce acute complications of sickle cell disease. Not prohibited in sport.

What the research used

The amounts, forms and durations published trials of L-glutamine actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Post-infectious irritable bowel syndrome with diarrhoea

    15 g

    Limited

    5 g three times daily · 8 weeks

    From one single-centre randomised trial reporting a large reduction in symptom scores and normalised intestinal permeability. The effect size was unusually large for this field and independent replication has not been published.

  • Studied for Immune and muscle outcomes in healthy athletes

    5–20 g

    Moderate

    Glutamine daily · Days to weeks

    Recorded because these doses were tested and did not produce consistent effects on infection rates, muscle mass or performance. Dosing here documents a null literature.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.

  • Split through the day

    Not enough

    The gut trial used three divided doses, because glutamine is rapidly taken up by enterocytes and plasma levels fall quickly. Divided dosing follows from that pharmacokinetics rather than from a tested comparison.

    Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.

The evidence in depth

Best supported: Limited

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Digestive comfort

Gut & Digestive Health
Limited evidence

One single-centre randomised trial reported a large improvement in symptoms and intestinal permeability in post-infectious irritable bowel syndrome with 15 g/day over eight weeks. It is a striking result from one site that has not been independently replicated, which is exactly the situation where enthusiasm usually runs ahead of the evidence.

What may be going on: Glutamine is the primary respiratory fuel of enterocytes and supports expression of tight junction proteins in laboratory models.

Limited evidence. Early human work, or mostly lab and animal research.

View the 3 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Immune function

Immune Health
Not enough evidence

Glutamine supplementation in healthy people, including athletes after prolonged exercise, has not reduced infection rates in controlled trials despite restoring plasma glutamine. The immunity claim is one of the clearer null results in sports nutrition.

Not enough evidence. Not enough human research to say anything useful yet.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Muscle protein synthesis

Muscle & Physical Performance
Not enough evidence

Trials of glutamine for muscle mass, strength or recovery in healthy trained people have consistently found no benefit over placebo when protein intake is adequate.

Not enough evidence. Not enough human research to say anything useful yet.

View the 2 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Worth knowing

    Critical illness and cancer

    A large multicentre trial of high-dose glutamine in critically ill patients with multi-organ failure found higher mortality in the glutamine group, which ended enthusiasm for routine use in intensive care. Separately, some tumours are glutamine-avid, and while there is no human evidence that supplementation promotes tumour growth, it is a reason to discuss it with an oncologist rather than assume.

  • Avoid

    Hepatic encephalopathy and severe liver disease

    Glutamine metabolism generates ammonia, which is the central problem in hepatic encephalopathy. Supplementation is inappropriate in advanced liver disease outside medical supervision.

  • Interaction

    Anticonvulsants

    Interacts withAnticonvulsants

    Because glutamine is a precursor to glutamate, additive effects with drugs acting on seizure threshold have been raised as a theoretical concern in people with epilepsy.

  • Worth knowing

    Instability in solution

    Free glutamine degrades in water to pyroglutamate and ammonia, faster when warm. Powder left dissolved in a bottle for hours is not delivering what the label says.

Evidence ratings on this page: 1 limited evidence, 2 not enough evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take L-glutamine, or a dose to follow.