Where is the research that glutamine affects athletic performance?

Glutamine Overview/Background

This question is not surprising as glutamine has been around for years now. In fact, I remember buying my first tub of glutamine powder back in 1997 when I was in college. I read all of the advertising and thought to myself, “I need some of that!” As your question states and related to athletic performance, there is very little data to illustrate a positive or ergogenic (performance-enhancing) effect for glutamine supplementation [1]. Two recent studies investigated resistance training performance along with glutamine supplementation and found no positive effect for glutamine use [2-3]. One of these studies had 31 individuals supplement with 0.9 g/kg lean mass of glutamine for 6 weeks and saw no differences in strength, lean tissue mass and protein degradation rates [3]. The other study had young individuals supplement with a single 0.3 g/kg body mass dose of glutamine or placebo 60 minutes before exercise and found no improvement in weightlifting performance [2]. Now before you throw your hands up in the air in disgust, this doesn’t necessarily mean it has no place being supplemented.

Much of the supportive research on glutamine relates to its being a primary fuel for cells in our digestive and immune systems [4]. Also consider that glutamine is the most abundant amino acid in blood plasma and skeletal muscle; comprising greater than 60% of the total intramuscular free amino acid pool [5]. These facts largely make up the primary reasons for why glutamine is popular among the body building sub-culture. As mentioned, glutamine is a primary fuel source for cells in our immune system [5-6], which makes supplementation an area of interest for endurance or athletes who exercise or train for prolonged periods of time. Considering this last point, cells of the GI tract and immune system are very active and turn over very fast, multiple times each day. If these cells don’t have enough glutamine or other critical amino acids to rebuild damaged or needed cellular protein, it will likely utilize the abundant supply of amino acids found within your skeletal muscle; easily the largest available depot of body protein and amino acids. In this light, decreases in glutamine has been associated with athletes experiencing overtraining or are partaking in very high-intensity training regimens [7].

Animal Studies

Is research available supporting its use? Absolutely! A number of studies performed in animals have supported the administration of glutamine for various metabolic outcomes, namely an improvement in nitrogen balance, improved balance of muscle protein metabolism, greater muscle protein synthesis and/or decreased muscle protein breakdown [8-12] while some have shown no impact [13-14].

Human Studies

A big misconception with glutamine is the fact that much of the human work with glutamine has been performed on patients recovering from surgery or other clinical scenarios, which greatly challenge the entire metabolic system every single minute of every single day. This isn’t the same case as someone who goes out to exercise for an hour or two each day. Similarly and while human studies have shown adding glutamine to stomach feeding improves nitrogen balance and minimized the loss of protein (but not necessarily muscle protein) [15-18], glutamine use requires very high dosages (20 grams/day) which must be sustained daily (before and after injury) to positively influence net protein balance and immune function [19-22]. In this light, several studies have suggested that providing glutamine does not provide any further advantage to improvements in lean muscle tissue while resistance training [23-24]. However, decreases in glutamine have been found in athletes with symptoms of overtraining or are participating in very high intensity exercise training [7]. Interestingly, glutamine may effectively serve as an energy recovery aid and boost the resynthesis of glycogen after exhaustive exercise if provided immediately after exercise at a dosage of 8 grams/day [25-26].

Other Things to Consider

All this being said, it is still an important aspect to consider that glutamine is classified as a conditionally essential amino acid. This means that under certain circumstances the body cannot make enough of it and adequate supply must come via dietary sources [27-28]. It’s safe to say that not every person produces and uses glutamine to the same extent. While one person may produce plenty of glutamine for what their body needs, other people may need to supplement with it just to maintain normal stores. This is one reason why using glutamine can’t be completely thrown out the window. The human body is drastically different and largely individualized. Many aspects of supplementation, including this example, become unique to the person and using a ‘cookie cutter’ approach may lack necessary insight.

Safety

The good news is that glutamine is relatively inexpensive (600 grams for $19.00; roughly a 30 – 60 day supply) and adding it to existing formulations or using it independently is safe and as mentioned previously not a cost issue. Further with the safety aspect, studies have used dosages of 0.3 grams per kilogram of body weight (22.5 grams for a 75-kg or 165-pound individual). As expected, glutamine levels in the blood increased, but toxicity levels in the blood did not change suggesting this dosage is well tolerated in healthy individuals [29]. Further, glutamine dosages of 0.285 and 0.570 grams per kilogram of body mass (21.3 – 43 grams for a 165-pound person) elicited no harmful effects after 5 days at this dosage [29] and 14, 21, and 28 grams/day caused no ill effects in another study [30-31].

Closing Thoughts

In summary, glutamine has some important physiological roles. No one should argue that. It is one of the best examples where strong (very strong) theoretical rationale does not always equate to positive outcomes with its use. It is fairly clear in the literature that additional dietary glutamine does very little to facilitate greater strength and/or gains in muscle mass. So one could say it certainly is not ergogenic or performance enhancing. However, considering the fact the glutamine is a major constituent of blood and muscle proteins and its demands grows when the body is under duress, supplementing your diet with 5 – 10 grams before and after exercise or a long training run may help to promote positive health.

References

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22. Novak, F., et al., Glutamine supplementation in serious illness: a systematic review of the evidence. Crit Care Med, 2002. 30(9): p. 2022-9.
23. Cribb, P.J., et al., The effect of whey isolate and resistance training on strength, body composition, and plasma glutamine. Int J Sport Nutr Exerc Metab, 2006. 16(5): p. 494-509.
24. Kerksick, C.M., et al., The effects of protein and amino acid supplementation on performance and training adaptations during ten weeks of resistance training. J Strength Cond Res, 2006. 20(3): p. 643-53.
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