L-Glutamine Questions and Answers

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Q1. What is glutamine?

Glutamine is the most abundant amino acid in the blood plasma and skeletal muscle (Antonio et al., 1999). Glutamine is also one of the major fuel sources of the gut and numerous cells of the immune system. Glutamine is produced in the body, but under certain circumstances such as injury, surgery or overtraining the body may not be able to synthesise sufficient glutamine to keep up with the demand (Miller, 1999). Under these conditions supplementary glutamine may be of benefit.

Q2. What does it mean when some people say glutamine is "conditionally essential"?

Amino acids are classified a either essential or non-essential. Essential amino acids are those that can't be synthesised (manufactured) by the body and therefore need to be obtained in the diet. Non-Essential amino acids can be synthesised in the body. Conditionally essential means that although glutamine can be synthesised by the body, under some conditions the body may not be able to synthesis enough glutamine to keep up with demand. Under these conditions glutamine supplementation may be beneficial.

Q3. What is the theoretical basis for glutamine supplementation?

As outlined in a recent scientific review there are numerous potential mechanisms by which glutamine could be of benefit to individuals participating in exercise (Antonio et al., 1999). These include:

• Preventing or lessening the severity of illness after intense training therefore allowing an athlete to return to training more quickly.
• Possible anticatabolic effects therefore sparing muscle protein
• Possible increase in cellular volume which may have an anabolic effect

Q4. Is there any scientific evidence to support the use of glutamine?

It has been reported that glutamine administered intravenously to patients following surgery have reported that glutamine can be effective at preventing protein breakdown. Consequently, glutamine supplementation may be of benefit in the context of rehabilitation from injury (Antonio et al., 1999). Furthermore the fact that glutamine is a fuel for certain cells of the immune system may indicate that glutamine may facilitate immune function. In endurance athletes one study reported that athletes supplemented with glutamine experienced a reduced incidence of infections in the days following strenuous training and competition (Castell et al., 1996). It is known that glutamine levels can decline with stress (Lacey et al., 1990), consequently it would seem that glutamine is most likely to be of benefit during periods of intense exercise or bodily stress.

Q5. What does glutamine look like?

Glutamine is basically a white powder that looks very similar to protein powder.

Q6. What dose of glutamine is recommended?

Research suggesting positive effects of glutamine on immune function administered five grams immediately post exercise and five grams 2 hours post exercise (Castell et al., 1996). This dosage resulted in a lower infection rate in the seven days following intense exercise and competition. Consequently the addition of 5-10 grams of glutamine to a sports drink or post exercise nutritional regime may offer significant benefit during periods of intense training.

Q7. Will glutamine produce large gains in muscle size and strength?

There has been much speculation as to how glutamine could be of benefit to athletes wanting to gain lean muscle mass. The fact that the cells of the gastrointestinal tract require a large supply of glutamine may mean that supplementary glutamine may offer anticatabolic effects and thereby spare muscle protein (Incledon et al., 2001).

A recent study investigated the effect of glutamine on strength and lean tissue mass during a 6 weeks resistance-training program (Candow et al., 2001). The study reported that glutamine did not enhance the adaptations to the strength-training program. However, the scientists suggested that the lack of any beneficial effect of glutamine in the study might have been attributed to the fact that the resistance-training program may not have been stressful enough (Candow et al., 2001). This conclusion would tend to be in line with current scientific opinions that indicate glutamine is most likely of use under conditions of stress (Antonio et al., 1999).

Unfortunately some marketing campaigns have resulted in unrealistic expectations surrounding glutamine. Glutamine should not be looked at as a supplement that will pack on mass and size, but rather is a supplement that may indirectly assist the athlete via potential immune stimulating effects (see question 8). The truth is if you wanted to pack on lean muscle mass and strength glutamine would not be your first choice of supplement (instead see Myocytin, Creatine or Mass Monster). However if you are an athlete looking for the edge you can probably appreciate that a two-week lay off due to an upper respiratory tract infection could certainly impair your performance. Many athletes stack glutamine with other mass building supplements (eg. Myocytin, Creatine or Mass Monster) in an attempt to maximise protein synthesis while simultaneously minimising the chance of developing infections during strenuous training.

Q8. Will consuming glutamine really reduce the number of illnesses experienced during intense training?

Research investigating infection rates in difficult to design and control. This is because so many factors can influence infections rates including diet, lifestyle, stress levels, training, exposure etc. However, a recent study monitored the infection rates in endurance athletes for seven days after intense training sessions or competitions. In the seven days post exercise 81% of the athletes in the glutamine group remained healthy and infection free, while only 49% remained infection free in the placebo group (Castell et al., 1996).

Figure 1: A comparison of the percentage of athletes experiencing no infections after intense training combined with either glutamine or placebo ingestion. The above graph suggests that glutamine enhanced immune function and prevented infection in athletes undergoing intense training and competition.

Q9. When is the best time to consume glutamine?

At present there has been no research investigating the optimal way to consume oral glutamine. It is known that strenuous exercise can decrease plasma glutamine concentrations and there may be an increased risk of developing infections (Castell et al., 1996). A recent study reporting reduced infections in athletes ingesting glutamine suggested that the provision of glutamine after strenuous exercise might restore physiological levels. The scientists further suggested that a greater availability of glutamine for key cells of the immune system during the post exercise period might be responsible for reducing infection rates (Castell et al., 1996). Therefore there would appear to be a theoretical rationale for consumption of glutamine immediately after exercise.

Q10. Is glutamine safe?

In recent years several studies have investigated the safety of glutamine supplementation. Glutamine appears to be well tolerated in human subjects with the available research suggesting that there is no clinical toxicity at researched dosages (Antonio et al., 1999). In fact Candow and co-workers (2001) reported no adverse effects in healthy young subjects consuming oral glutamine dosages approximating 45g per day. Furthermore, glutamine has been administered to ill hospital patients without any adverse effects (Antonio et al., 1999). Together this would tend to indicate that glutamine is well tolerated and not associated with toxicity at the dosages administered for therapeutic and sports supplementation purposes. However, before beginning any new exercise or dietary intervention it is advised that you consult with a medical physician.

Q11. Is glutamine supplementation only for athletes?

Glutamine use is certainly not limited to athletes. Research is continuously being released that is facilitating our scientific understanding of what physiological effects glutamine has and how it can best be used. At present it does appear that glutamine is best consumed during periods of stress. Stress can arise form in a number of forms and this may include injury, work related stressors, or excessive physical activity such as seen in overtraining syndrome. Consequently glutamine may be just as likely to offer immuno-protective and other beneficial physiological effects to the time challenged executive as the elite athlete.

Q12. Would glutamine result in a positive drug test?

No, glutamine is not a drug or banned substance. Glutamine is not listed on the current World Anti Doping Association (WADA) prohibited list (WADA, 2004). Therefore, glutamine can be considered a safe supplement, even in elite athletes subjected to regular drug testing.

References
1. Antonio, J. and Street, C. Glutamine: a potentially useful supplement for athletes. Canadian journal of applied physiology. 24:1-14, 1999.

2. Candow, D.G., Chilibeck, P.D., Burke, D.G., Davison, K.S. and Smith-Palmer, T. Effect of glutamine supplementation combined with resistance training in young adults. European journal of applied physiology 86, 2001.

3. Castell, L.M., Poortmans, J.R. and Newsholme, E.A. Does glutamine have a role in reducing infections in athletes? European journal of applied physiology and occupational physiology 73: 488-490, 1996.

4. Incledon, T. and Antonio, J. The Anticatabolics. In Antonio, J. and Stout, J.R. (Eds). Sports Supplements. Lippincott, Williams and Wilkins. Philadelphia. pp 113-136, 2001.

5. Lacey JM. Wilmore DW. Is glutamine a conditionally essential amino acid? Nutrition Reviews. 48:297-309, 1990

6. Lehmkuhl, M., Justice, B., Pistilli, E., Trone, G., Malone, M., Vinci, D., Utter, A., Kilgore, J.L., Haff, E. and Haff, G. The effect of eight weeks of creatine and glutamine supplementation on body composition and performance. Journal of strength and conditioning research 15:396, 2001.

7. Miller AL. Therapeutic considerations of L-glutamine: a review of the literature. Alternative Medicine Review. 4:239-48, 1999.

8. World Anti Doping Agency prohibited list (2004). Available online: http://www.wada-ama.org/en/t1.asp