In 30 seconds
- Glutamine is the most abundant free amino acid in the body: it makes up 50-60% of the free amino acids in muscle.
- Long, hard exercise lowers its blood level for a few hours, which is why it has been studied so much in athletes.
- In studies it reduced markers of fatigue and muscle damage, and in runners in the heat it lowered intestinal permeability from 0.25 g per kilo of lean mass.
- Its territory is recovery, not muscle: with strength training, 6 weeks of glutamine gave the same gains as placebo.
Glutamine is an amino acid that your body makes and that you also get from the protein in your diet. Studies have looked at it mainly for recovery after hard exercise, for immunity and for the gut. For building muscle, on the other hand, it has shown no effect.
Glutamine in your body
The most abundant free amino acid, in figures
What glutamine is
It is the most abundant free amino acid in your body. In fasting blood there are between 550 and 750 µmol/L, more than 20% of all the amino acids in circulation. And in muscle it makes up 50-60% of the free amino acids 1.
It is considered “conditionally essential”: you normally make as much as you need, but in situations of heavy wear and tear, such as long, exhausting exercise, demand can outstrip what you produce 1.
What does your body use it for? It is one of the preferred fuels of your immune cells: they use it at a rate equal to or higher than glucose. The gut, the liver and the muscles regulate how much of it passes into the blood 2.
Where it is found
In every food that contains protein, of both animal and plant origin 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.
What happens to it with exercise
After a marathon, blood glutamine falls for about 6-9 hours 1. Periods of very hard training have also been linked to lower levels. That is where the idea came from that supplementing it might help an athlete's immune defences 3.
Glutamine and strength
Strength in 6 weeks: the same with glutamine as with placebo
What the studies say
| For | What has been seen |
|---|---|
| Fatigue and muscle damage | Less ammonia and fewer markers of muscle damage in several studies |
| The gut in the heat | Lower intestinal permeability in a trial with runners at 30 °C |
| Immunity | Mixed results depending on the study |
| Muscle and performance | No difference from placebo in most studies |
Sources: Coqueiro et al., 2019; Pugh et al., 2017; Castell et al., 1996; Ramezani Ahmadi et al., 2019.
Fatigue and muscle damage
The most comprehensive review on glutamine and fatigue found that it 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 markers of muscle damage, such as creatine kinase, in several studies, although much of that data comes from animals 1.
For glycogen, the fuel your muscles store, the results are mixed: some studies found larger stores and others did not 1.
Immunity
This is where it all started: a 1996 study of 151 athletes, who had two drinks after exercise, led to research into glutamine and immune defences 4.
In later studies, glutamine keeps its blood level up after exercise, but it does not prevent several of the immune changes that happen afterwards 3. And a meta-analysis of 25 trials found no overall effect on athletes' immune systems 5.
The gut when you run in the heat
This is one of the most interesting lines of research. A team of researchers measured intestinal permeability, that is, how much the gut lets substances that should stay inside pass into the blood, in runners in the heat.
In their trial, 10 men ran for 60 minutes at 30 °C after taking glutamine or placebo 2 hours earlier. With all three doses tested, from 0.25 to 0.9 g per kilo of lean mass, permeability fell, and the higher the dose, the more it fell 6. The lowest dose is equivalent to about 15 g for a 70 kg person.
Stomach discomfort did not change, so it remains to be seen whether this makes a noticeable difference in practice 6. If you train in summer, you will find more tips in training in the heat.
Muscle, strength and performance
Here the results are clear. In a trial with 31 young adults who did strength training for 6 weeks, glutamine added nothing: both groups improved by 30% in the squat and 14% in the bench press 7.
The meta-analysis of 25 trials also found no change in lean mass, body fat or aerobic performance 5. For building muscle, what works is complete protein and training; if you are interested in the role of amino acids, you will find it in BCAAs and leucine: what the studies say.
How much is safe
Glutamine: the safe level and what was tolerated in studies
How much, and is it safe
- Doses in the studies: highly variable, from less than 1 g up to 0.9 g per kilo of lean mass 1 6.
- Tolerance: healthy adults have taken 20-30 g at once with no adverse effects 3.
- Safe level: the reference risk assessment sets the observed safe level at 14 g a day 8.
If you have kidney or liver disease, are pregnant or take medication, check with your doctor before taking amino acid supplements.
We go into more detail, study by study, in glutamine: what the studies say.
The glutamine in Nitrus
Nitrus Isotonic includes glutamine within a hydration formula: three types of carbohydrate, five electrolytes, 1 g of BCAA 2:1:1, 200 mg of taurine and all 13 vitamins at 100% of the NRV. Riboflavin (vitamin B2), vitamins B6, B12 and C, niacin, pantothenic acid and folate contribute to the reduction of tiredness and fatigue. A varied and balanced diet and a healthy lifestyle are important.
Frequently asked questions
What is glutamine good for?
It is the most abundant free amino acid in your body and one of the fuels of your immune cells. In athletes, studies have linked it to fewer markers of fatigue and muscle damage, and to lower intestinal permeability when running in the heat.
Does glutamine help you build muscle?
That is not its territory. In a 6-week strength training trial, those who took glutamine gained the same strength and lean mass as with placebo, and a meta-analysis of 25 trials also found no change in lean mass.
How much glutamine can you take a day?
The reference risk assessment sets the observed safe level for healthy adults at 14 g a day. In single-dose studies, 20-30 g have been taken at once with no adverse effects.
Which foods contain glutamine?
It is in every food that contains protein. Beef has about 1.2 g per 100 g, and eggs and tofu about 0.6 g.
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
- 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
- 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
- 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.
