In 30 seconds
- Glutamine is the most abundant free amino acid in the body: 550-750 µmol/L in fasting blood and 50-60% of the free amino acids in muscle.
- Its most consistent effects are on markers of fatigue and muscle damage: less ammonia and less creatine kinase in several studies.
- In runners in the heat, 0.25 to 0.9 g per kilo of lean mass reduced intestinal permeability, more so the higher the dose.
- Across 25 trials, it did not change lean mass or aerobic performance. Up to 14 g a day is the observed safe level.
Glutamine has been studied a great deal in athletes, mainly because of its links with fatigue, muscle damage, immunity and the gut. Here is what the studies found, organised by outcome and by level of evidence.
Most abundant free amino acid
The glutamine in your body, in three figures
What it is and what your body uses it for
It is the most abundant free amino acid in the body. In fasting blood there are between 550 and 750 µmol/L, more than 20% of the amino acids in circulation. In muscle it makes up 50-60% of the free amino acids. Slow-twitch muscle contains about 3 times as much as fast-twitch muscle 1.
You normally make as much as you need, but in situations of heavy wear and tear, such as long, exhausting exercise, demand can outstrip production. That is why it is considered “conditionally essential” 1.
Your immune cells use it at a rate equal to or higher than glucose. The gut, the liver and the muscles are what regulate how much of it passes into the blood 2.
Where it is found
In every food that contains protein 2:
| Food | Glutamine |
|---|---|
| Beef | 1.2 g |
| Tofu | 0.6 g |
| Egg | 0.6 g |
| Sweetcorn | 0.4 g |
| Skimmed milk | 0.3 g |
| White rice | 0.3 g |
Source: Cruzat et al., 2018. Approximate values.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Markers of muscle damage | Moderate | Less creatine kinase and myoglobin in several studies; some of the data come from animals. |
| Ammonia and fatigue | Moderate | Less ammonia during exercise, especially when taken for more than 5 days and in intermittent efforts. |
| Recovery of strength | Low | Faster recovery with leucine and glutamine together in one trial; few studies with glutamine alone. |
| Intestinal permeability in the heat | Preliminary | One trial with 10 runners: less permeability with all three doses tested. |
| Immunity | Low | Maintains its blood level after exercise; no overall effect on immunity in a meta-analysis. |
| Muscle mass, strength and aerobic performance | No clear effect | Same gains as with placebo in the training trials. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Ramezani Ahmadi et al., 2019 | Meta-analysis | 47 studies reviewed, 25 in the analysis | No overall effect on immunity, aerobic performance, lean mass or body fat. Fewer neutrophils with more than 200 mg/kg. 4 |
| Coqueiro et al., 2019 | Review | Studies in humans and animals | Less ammonia and fewer markers of muscle damage; limited effect on physical performance. 1 |
| Gleeson, 2008 | Review | Studies in athletes | Maintains blood glutamine after exercise, but does not prevent several immune changes. 20-30 g at once, with no adverse effects. 3 |
| Córdova-Martínez et al., 2021 | Placebo-controlled crossover trial | 12 professional basketball players | 6 g a day for 20 days: lower creatine kinase and myoglobin than with placebo. 6 |
| Waldron et al., 2018 | Placebo-controlled trial | 23 men | After 100 drop jumps, leucine with 0.3 g/kg of glutamine: strength and jump recovered sooner at 48 and 72 hours. 7 |
| Pugh et al., 2017 | Placebo-controlled crossover trial | 10 active men | 60 minutes of running at 30 °C: less intestinal permeability with 0.25, 0.5 and 0.9 g/kg of lean mass, 2 hours beforehand. 8 |
| Candow et al., 2001 | Placebo-controlled trial | 31 young adults, 6 weeks of strength training | 0.9 g/kg of lean mass a day: same gains in strength and lean mass as with placebo. 9 |
Exercise and blood glutamine
After a marathon, blood glutamine falls for about 6-9 hours. On the other hand, a study in ultra-triathlon found no change 1.
Periods of very hard training have been associated with lower levels. That was put forward as one of the causes of the dip in immune defences after exercise 3. If you take glutamine, its blood level rises sharply within 30 minutes and returns to baseline in about 2 hours 1.
Fatigue and muscle damage
This is where the results are most consistent. The review by Coqueiro and colleagues found that glutamine reduces the build-up of ammonia during exercise. The effect was greater when it was taken for more than 5 days in a row and in intermittent efforts. It also lowered creatine kinase and LDH, two markers of muscle damage, in several studies 1.
In a study with 12 professional basketball players, 6 g a day for 20 days left creatine kinase and myoglobin lower than with placebo. Its authors see glutamine as useful in sports with lots of eccentric actions, such as basketball itself 6.
Combined with leucine, in a trial with 23 men, it sped up recovery after 100 drop jumps: more strength and a better jump at 48 and 72 hours than with placebo 7. Leucine alone also helped, so not everything can be attributed to glutamine.
For glycogen, the results are mixed, and the effect on physical performance is limited 1.
Immunity
The idea dates back to the 1990s. In Castell's classic study, 151 athletes took glutamine or placebo right at the end of exercise and 2 hours later 5.
Later studies are less clear. Glutamine keeps its blood level up after exercise, but it does not prevent several of the immune changes that happen afterwards. In addition, its level does not fall far enough to hold back lymphocytes 3. The meta-analysis by Ramezani Ahmadi found no overall effect on athletes' immune systems 4.
Pugh's trial, 2017
How glutamine was tested running in the heat
The gut and heat
In Pugh's trial, 10 men ran for 60 minutes at about 10 km/h in a room at 30 °C. Two hours beforehand they took placebo or glutamine at three doses: 0.25, 0.5 and 0.9 g per kilo of lean mass 8.
Intestinal permeability fell with all three doses, and most with the highest. Stomach discomfort, which was minor, did not change 8. The authors conclude that people who compete in the heat could benefit, although it remains to be seen whether this shows up in symptoms. If you train in summer, you will find more tips in training in the heat.
Muscle, strength and performance
Here the studies agree. In Candow's trial, 31 young adults did strength training for 6 weeks with 0.9 g of glutamine per kilo of lean mass a day or with placebo. Both groups gained the same: 30% in the squat, 14% in the bench press and around 2% in lean mass 9.
The meta-analysis of 25 trials also found no change in lean mass, body fat or VO₂max 4. For muscle, what counts is complete protein; we look at this in BCAAs and leucine: what the studies say.
Safety
Grams of glutamine a day: the observed safe level
Doses and safety
| Study | Dose | For a 70 kg person |
|---|---|---|
| Basketball (Córdova-Martínez, 2021) | 6 g a day for 20 days | 6 g a day |
| Muscle damage (Waldron, 2018) | 0.3 g per kilo, with leucine | About 21 g |
| Gut in the heat (Pugh, 2017) | 0.25-0.9 g per kilo of lean mass, 2 hours beforehand | About 15-54 g |
| Strength (Candow, 2001) | 0.9 g per kilo of lean mass a day, 6 weeks | More than 50 g a day |
The 70 kg column is a guide. Lean mass is taken from the example in Pugh et al.: 70 kg with 15% body fat.
- Tolerance: healthy adults have taken 20-30 g at once with no adverse effects, and athletes 28 g a day for 14 days 3.
- Safe level: the reference risk assessment sets the observed safe level in healthy adults at 14 g a day 10.
- Caution: if you have kidney or liver disease, are pregnant or take medication, check with your doctor.
And Nitrus?
Nitrus Isotonic is our hydration formula, and it includes glutamine: three types of carbohydrate, five electrolytes, all 13 vitamins at 100% of the NRV, 1 g of BCAA 2:1:1 and 200 mg of taurine. The studies on this page are about glutamine as an ingredient, not about any specific product. You will find the practical summary in glutamine: what it does.
Frequently asked questions
What do the studies say about glutamine?
That it reduces markers of fatigue and muscle damage, such as ammonia and creatine kinase, and that in runners in the heat it lowered intestinal permeability. On the other hand, it has shown no effect on muscle mass, strength or aerobic performance.
Does glutamine support the immune system?
The results are mixed. Taken after exercise, it maintains its blood level, but it does not prevent several of the immune changes that happen afterwards. A meta-analysis of 25 trials found no overall effect on immunity.
When is glutamine taken in the studies?
It depends on the goal: 2 hours before running in the heat in the studies on the gut, just after exercise in those on immunity, and daily for weeks in those on muscle damage.
Is glutamine safe?
In healthy adults, the reference risk assessment sets the observed safe level at 14 g a day, and 20-30 g have been taken at once with no adverse effects. If you have kidney or liver disease, check with your doctor.
Sources
- Coqueiro AY, Rogero MM, Tirapegui J. Glutamine as an anti-fatigue amino acid in sports nutrition. Nutrients. 2019;11(4):863. View publication
- Cruzat V, Macedo Rogero M, Noel Keane K, Curi R, Newsholme P. Glutamine: metabolism and immune function, supplementation and clinical translation. Nutrients. 2018;10(11):1564. View publication
- Gleeson M. Dosing and efficacy of glutamine supplementation in human exercise and sport training. J Nutr. 2008;138(10):2045S-2049S. View publication
- Ramezani Ahmadi A, Rayyani E, Bahreini M, Mansoori A. The effect of glutamine supplementation on athletic performance, body composition, and immune function: a systematic review and a meta-analysis of clinical trials. Clin Nutr. 2019;38(3):1076-1091. View publication
- Castell LM, Poortmans JR, Newsholme EA. Does glutamine have a role in reducing infections in athletes? Eur J Appl Physiol Occup Physiol. 1996;73(5):488-490. View publication
- Córdova-Martínez A, Caballero-García A, Bello HJ, Pérez-Valdecantos D, Roche E. Effect of glutamine supplementation on muscular damage biomarkers in professional basketball players. Nutrients. 2021;13(6):2073. View publication
- Waldron M, Ralph C, Jeffries O, Tallent J, Theis N, Patterson SD. The effects of acute leucine or leucine-glutamine co-ingestion on recovery from eccentrically biased exercise. Amino Acids. 2018;50(7):831-839. View publication
- Pugh JN, Sage S, Hutson M, et al. Glutamine supplementation reduces markers of intestinal permeability during running in the heat in a dose-dependent manner. Eur J Appl Physiol. 2017;117(12):2569-2577. View publication
- Candow DG, Chilibeck PD, Burke DG, Davison KS, Smith-Palmer T. Effect of glutamine supplementation combined with resistance training in young adults. Eur J Appl Physiol. 2001;86(2):142-149. View publication
- Shao A, Hathcock JN. Risk assessment for the amino acids taurine, L-glutamine and L-arginine. Regul Toxicol Pharmacol. 2008;50(3):376-399. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
