L-Glutamine
An amino acid the body makes, best known for training and gut comfort.
- Training and recovery
- Gut lining
- Gut comfort
- Muscle strength
- Inflammation and antioxidants
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is L-Glutamine?
Glutamine is the most plentiful amino acid in the body, and one of the busiest: the gut, the liver and skeletal muscle between them set how much is circulating at any moment. The body makes its own and food adds more, so it is usually called non-essential, though reviews describe it as becoming essential when the body is under heavy strain. Immune cells and the cells lining the intestine are among its largest customers, using it at a rate reviews put alongside glucose. On a UK shelf it is plain L-glutamine, a powder or a capsule, with no competing chemical forms to weigh up.
Why do people take L-Glutamine?
Training and recovery
The thinking. Glutamine has been a fixture of the sports aisle for decades, taken after hard sessions and through heavy training blocks. The thinking runs through the immune system: reviews describe immune cells as spending glutamine at a rate matching their use of glucose, and exhausting exercise as a state where the body’s own supply falls behind.
What research has found. A review pooling twenty-five trials in adults who train measured aerobic fitness, body composition and white blood cell counts, and found no clear difference from placebo. Body weight was the exception, a little lower on average, and one kind of white cell fell at larger doses. Research here is still young: a few studies so far, mostly pointing the same way.
Gut lining
The thinking. The gut is one of glutamine’s biggest everyday customers: reviews describe it as a main fuel for the cells lining the intestine, and as having a hand in the tight junctions that seal one cell to the next. Feeding that lining is what people mean when they take it for a leaky gut.
What research has found. Ten trials pooled together, 352 adults in all, measured how much passes through the gut lining and found no clear difference overall, though trials using more than 30 g a day did show a reduction. The two smaller trials differed: in adults with Crohn’s disease, readings improved as much on the whey protein it was compared against, while in ten men running in the heat a dose beforehand lowered them. A fair body of trials has looked at this, and most point the same way.
Gut comfort
The thinking. Others take it for how the gut feels day to day, and for the months after a bout of food poisoning or a stomach bug. The thinking is the same as for the lining: a better-fed lining, and a calmer day.
What research has found. A review of seven trials in adults with inflammatory bowel disease found no clear difference in symptoms or disease activity, whichever way it was given. An eight-week trial in adults whose irritable bowel followed a gut infection measured large falls in symptom scores: roughly four in five met its target on glutamine, against about one in twenty on placebo. Only a few studies have measured this so far, though they mostly agree.
Muscle strength
The thinking. Most of the body’s free glutamine sits in skeletal muscle, which also releases it into the blood for the gut and liver to spend. The thinking is that keeping that store topped up leaves more of it where it started. It is a quieter, newer reason than training.
What research has found. One trial gave glutamine or placebo for thirty days to women aged 60 to 80, some in exercise classes and some not, and measured the torque and power of the knee muscles. Readings were higher after the month than before it in the groups taking glutamine, most clearly among those exercising as well. Few studies have measured this yet, so there is little to go on either way.
Inflammation and antioxidants
The thinking. Glutamine has a quieter reputation as something the body leans on under strain. Reviews describe it feeding into glutathione, one of the body’s own antioxidants, and into the heat shock proteins a cell calls up when it is stressed. People thinking about the wear of a hard training block pick it up for that.
What research has found. A review gathered six trials in adults living with long-term conditions and measured blood markers of inflammation and oxidation. Three measured lower C-reactive protein, a general marker of inflammation; of the three measuring an inflammatory signal called TNF-alpha only one found a fall, and the two measuring oxidation markers disagreed. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
What does L-Glutamine do in the body?
Glutamine is the most plentiful free amino acid in the body, and it never sits still. Skeletal muscle, the liver and the gut between them set how much is in the blood at any moment: muscle mostly releases it, the gut mostly spends it.
What spends it is the other half of the story. Fast-dividing cells take a great deal: the lining of the intestine, and the white cells of the immune system, whose demand reviews put alongside their demand for glucose. They burn it for energy and use its nitrogen to build new material; it also feeds into glutathione, one of the body’s own antioxidants, and into the heat shock proteins a cell calls up under strain. The body can turn it into proline as well, one of the building blocks of collagen.
What do people say about taking L-Glutamine?
These are anecdotes people have shared, not evidence.
What people like
- Quicker recovery between hard sessions is the commonest good report, several describing fewer aches and more training days in a week.
- Some who took it for years for gut trouble describe flare-ups settling sooner, and a few mention fewer colds through heavy training.
- A handful say a teaspoon stirred into water blunts sugar cravings within minutes, usually alongside a low-carbohydrate way of eating.
- Several describe sleeping better and feeling steadier on it, though most say they cannot separate it from their training and diet.
Common complaints
- Stomach pain, loose bowels and a raw feeling in the gut come up often, sometimes at doses as small as a pinch.
- Noticing nothing at all is just as common, particularly among long-time lifters, several of whom call it money they would not spend again.
- A few describe mood or sleep going the wrong way after some weeks: nervousness, low mood, or insomnia returning at ten grams.
- Some report early effects fading after a month or two, and a minority describe an odd, crashing feeling on anything but a small dose.
How people take it
- Five grams a day, a level teaspoon stirred into water or a shake, is much the commonest routine, usually with a meal.
- Training regulars go higher: two to ten grams daily, another ten or so after a session, and up to thirty in hard blocks.
- Those with sensitive guts very commonly start at a fraction of a gram and build the amount up over weeks or months.
- Powder is the usual form; many take it with a protein shake, and some split it between morning, after training and bedtime.
Read from these public discussions:
- L-glutamine dosage (StrongFirst forums, 2012)
- Glutamine question (StrongFirst forums, 2014)
- Glutamine Supplementation (AnandTech forums, 2005)
- Has anyone used L glutamine for blood sugar issues? (Phoenix Rising forums, 2012)
- Can Glutamine do this? (Phoenix Rising forums, 2014)
- Glutamine side effects (Phoenix Rising forums, 2016)
What forms of L-Glutamine are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| L-glutamine | Plain L-glutamine, the amino acid itself; trials used it as a powder stirred into water. | 500 mg to 5 g |
What else is worth knowing about L-Glutamine?
- The trials behind this page used fifteen to thirty grams a day, or a single dose worked out from body weight before exercise. Where reviews looked for a dose pattern, differences showed above 30 g a day for what passes through the gut lining.
- The eight-week bowel trial recorded side effects as often on placebo as on glutamine, and no serious ones; the other studies behind this page did not report on them.
- Who took part varies: adults who train, recreational runners, women aged 60 to 80, adults with bowel conditions and adults living with long-term illness; several trials were small. Much of the wider glutamine literature is hospital work, given by drip or feeding tube or alongside cancer care, and none of it lies behind the reasons above.
- Labels give glutamine per serving, and a serving is often a level scoop or more than one capsule, so the figure on the front is not always what one capsule holds.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (14 studies)
- The effect of glutamine supplementation on athletic performance, body composition, and immune function: A systematic review and a meta-analysis of clinical trials. (2019, meta-analysis)
- A systematic review and meta-analysis of clinical trials on the effects of glutamine supplementation on gut permeability in adults. (2024, meta-analysis)
- Glutamine supplementation reduces markers of intestinal permeability during running in the heat in a dose-dependent manner. (2017, randomised trial)
- Glutamine and whey protein improve intestinal permeability and morphology in patients with Crohn's disease: a randomized controlled trial. (2012, randomised trial)
- Effects of glutamine supplementation on inflammatory bowel disease: A systematic review of clinical trials. (2021, systematic review)
- Randomised placebo-controlled trial of dietary glutamine supplements for postinfectious irritable bowel syndrome. (2019, randomised trial)
- L-Glutamine Supplementation Enhances Strength and Power of Knee Muscles and Improves Glycemia Control and Plasma Redox Balance in Exercising Elderly Women. (2021, randomised trial)
- The effects of glutamine supplementation on inflammatory and oxidative stress indices in chronic diseases: a systematic review. (2026, systematic review)
- Glutamine: Metabolism and Immune Function, Supplementation and Clinical Translation. (2018, review)
- Glutamine and cancer: metabolism, immune microenvironment, and therapeutic targets. (2025, review)
- The Roles of Glutamine in the Intestine and Its Implication in Intestinal Diseases. (2017, review)
- The Emerging Role of l-Glutamine in Cardiovascular Health and Disease. (2019, review)
- Proline metabolism and cancer: emerging links to glutamine and collagen. (2015, review)
- Glutamine for Amelioration of Radiation and Chemotherapy Associated Mucositis during Cancer Therapy. (2020, review)
How much does L-Glutamine cost?
That depends on the form and the pack, so we work out the price of the same dose of every L-Glutamine product we can find and rank them.