Glutamine is a sports supplement that has grown in popularity over the years, principally due to claims it can support strength and lean mass gains. As I hope to show in this post, the roles of glutamine in the body go far beyond just muscle protein synthesis … but that does not necessarily mean you’ll see a benefit from supplementation.
What is it?
Glutamine is one of the most prevalent amino acids in animals, such as humans! It is what is known as a ‘conditionally essential’ amino acid. This means that we synthesise it in our bodies, but in certain (stress) states we cannot produce it at the rate it is required, and so we also need to obtain it exogenously (from our diet) (see Lacey and Wilmore 1990). These stress states include severe burns, wounding, cachexia, and disease.
What does it do?
Short answer: a lot! Drawn out below are those factors most relevant and studied in relation to glutamine and physical training.
As an amino acid, glutamine is of course a building block for protein … including muscle protein. Supplementing with glutamine has been shown to benefit recovery after serious physical trauma, such as severe burns and knife wounds, or in the case of muscle wasting diseases (Soeters and Grecu 2012). In these scenarios, the rate of many of the processes that glutamine is involved in are upregulated and it is plausible that the body becomes glutamine deficient – supplementation can therefore restore physiological levels of glutamine, and glutamine function. However, studies have failed to show an effect of glutamine supplementation on muscle growth in the absence of trauma – it seems likely that glutamine is not a limiting factor for muscle maintenance and growth under ‘non-trauma’ conditions (see Phillips SM 2014).
Glutamine is the preferred energy source for certain immune and gut cells, as it provides them with more immediate energy source than glucose (see Lacey and Wilmore 1990). Glutamine can also be converted to glucose (gluconeogenesis), to provide energy for cells throughout the body.
Glutamine can also play a role in controlling the release of energy from the carbs we eat. Ingesting glutamine (or any protein source) alongside carbs appears to blunt the blood glucose and insulin spikes (and so we would assume the energy high and then low) that would otherwise occur in response to consuming carbs (Awad et al 2011). As an aside – this is one of the reasons why it is recommended to take protein plus carbs as fuel during endurance exercise, and not just carbs … the protein helps provide a slower release of energy over time from the calories consumed.
Glutamine is the precursor for the antioxidant glutathione, and therefore plays an important role in protecting our bodies against oxidative damage from the so-called ‘free radicals’ that are produced by our bodies as they carry out the normal metabolism they need so that we can live. This damage can cause our cells to function incorrectly and wear out quicker, requiring energy and resources to repair and replace.
Glutamine also appears to have a role in the immune system and infection control. Endurance exercise of over 1 hour has been shown to decrease the amount of glutamine circulating around the body and increase the risk of infection (marathon runners and other long distance athletes are, all else being equal, more susceptible to infectious disease). Glutamine supplementation has been shown not only to restore glutamine levels, but also to reduce the risk of infection – indicating a causal role for glutamine in this, although the mechanism by which glutamine acts is not yet understood (Castell and Newsholme 1997, Gleeson M 2008).
Glutamine supplementation during endurance exercise may improve performance, by reducing blood ammonia concentrations (Carvalho-Peixoto et al 2007). No improvement has been found in resistance or explosive exercise (Candow et al 2001, Haub et al 1998, Antonio et al 2002). There may be several reasons for the improvement in endurance athletes – perhaps because glutamine is used as an energy source, its role in carbohydrate metabolism, its antioxidant or immune boosting properties … and / or something yet to be discovered!
How do we get it?
Glutamine is perhaps unsurprisingly found in high levels in meat and eggs, i.e. animal tissue! It is also found in very high levels in whey (~2g / 15g protein) and casein (~2g / 15g protein).
Should I supplement with it?
It depends. If you have low levels of antioxidants or glutamine in your diet, if you are sick, or if you are doing a cardio or endurance based activity for more than an hour, then you might consider supplementing after talking with an appropriate professional.
Other than that, my personal view is no. If you eat a diet containing meat, whey and casein you are going to be obtaining a relatively high amount of dietary glutamine as it is. And glutamine is not stored in the body – any excess will simply be converted to something else. And more than this, excessive glutamine intake could lead to excessive ammonia levels in serum, which can lead to liver, kidney and heart damage – this is because when you take in too much protein and cannot use it all, the amino acids are converted to other things and the nitrogen groups in them are released as ammonia.
The lowest level of glutamine supplementation that has been shown to result in excessive ammonia in serum is 0.65g/kg bodyweight (see Gleeson M 2008), but of course the exact amount will vary from individual to individual.
Candow, DG, Chilibeck PD, Burke DG, Davison KS, Sith-Palmer T. Effect of glutamine supplementation combined with resistance training in young adults. Eur J Appl Physiol. 86(2):142-9, 2001
Castell LM, Newsholme, EA. The effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise. Nutrition 13:738 – 742, 1997
Gleeson, M. Dosing and Efficacy of Glutamine Supplementation in Human Exercise and Sport Training. Journal of Nutrition 138(10):2045S-2049S, 2008
Phillips, SM. A Brief Review of Critical Processes in Exercise-Induced Muscular Hypertrophy. Sports Med. 44 (Suppl 1): 71–77, 2014