American Fitness Professionals & Associates

By Matt Samuels, RD

Recently athletes have been inundated with information over glutamine and how it can possibly help them increase performance (or at least prevent overtraining).

Unfortunately, many athletes don’t know what glutamine is, where it can be found, how much to take, and, most importantly, if it works. Therefore, the purpose of this article is to address these issues and provide the necessary information to allow the consumer to make an educated decision regarding glutamine supplementation.

What Is Glutamine?

Glutamine is the most abundant amino acid in the human body, constituting 60% of the total intracellular amino acid pool (1). Glutamine’s functions include (a) a precursor to the synthesis of proteins, (b) nitrogen donator for the synthesis of purines, pyrimidines, and nucleotides (constituents of RNA and DNA), (c) a nitrogen transporter between various tissues, (d) a substrate for the production of ammonia, and (e) a metabolic fuel source for cells of the immune and
gastrointestinal system.

Glutamine is classified as a nonessential amino acid, which means the body is able to synthesize it. Therefore, we do not need to obtain glutamine from food sources in order to survive. However, data are now available that show glutamine to be an essential amino acid during certain catabolic states (2).

While these catabolic conditions encompass a wide variety of traumas and diseases such as burns or major surgery, glutamine is also important for the athlete since exercise induces a catabolic state, with the severity of catabolism being dependent on the intensity, duration, and frequency of exercise.

Current Research Findings

There has been some very exciting research emerging in recent years over glutamine and its role in anabolism and anticatabolism. However, the majority of  these studies have been performed on hospitalized patients who had varying degrees of injury or trauma. Fortunately, because the physiological response to intense exercise is somewhat similar to trauma, just usually not as profound, many believe these data can be extrapolated to the athlete with great success.

To save time and space I refer any reader who enjoys detail to reference #3 and #8, which contain great reviews of some recent clinical research involving glutamine.

To summarize some of these studies, it has been found that in patients with varying degrees of trauma or injury, glutamine supplemented both orally or via TPN (intravenously) maintained muscular glutamine concentrations, improved nitrogen balance, increased protein synthesis, decreased 3-methylhistidine excretion (a marker of muscle catabolism), avoided trauma related intestinal atrophy, improved weight gain in nonhematological patients, and reduced the length of hospital stay. It has also been shown that in athletes undergoing strenuous exercise, glutamine may decrease the risk of infections by up to 32%
(4) and be a useful indicator of an overtrained state (5). It is hypothesized that glutamine helps perform these anabolic and anticatabolic functions by increasing cellular hydration and acting as a vital substrate to various cells.

This may be a valid hypothesis since research has shown that glutamine facilitates a cellular hydration state (6) and that muscle glutamine concentration is positively correlated with the rate of muscle protein synthesis and the RNA/protein ratio, and inversely correlated with the rate of protein degradation (8, 9). 

What Can Glutamine Do For Me?

Based on the information presented, glutamine has great potential for improving athletic performance via decreased muscle damage and recovery time. Here’s how the various research findings might apply to athletes. Glutamine has been shown to improve nitrogen balance, increase protein synthesis, and decrease 3-methylhistidine excretion. This possibly means faster recovery for both the
endurance and strength athlete, along with faster muscle growth. Also, glutamine improved weight gain in nonhematological patients, which is linked to decreases in muscle wasting via the above mechanisms. Again, this may provide strength athletes, such as bodybuilders, with a better chance of reaching their goal of increased lean muscle mass.

Since glutamine also plays a role in the integrity of the immune system by acting as a key substrate for both lymphocytes and macrophages (8), supplementing with glutamine may help keep the immune system strong and decrease the risk of catching a cold during frequent, intense, lengthy training sessions.

Also, because glutamine increases gut mucosal integrity and intestinal functioning, it’s possible that the food we eat may be absorbed better or that we may have less GI distress after eating certain foods. Finally, glutamine has been shown to stimulate the accumulation of muscle glycogen in rats (7). If this same mechanism occurs in humans, this could provide an added advantage for the endurance athlete, who relies heavily on glycogen stores for energy. 

How Much Glutamine Do I Need?

After reading this article you may be interested in trying glutamine. First, dosages must be mentioned. There is no standard dosage, such as with creatine, that has been used in the studies mentioned previously. Typically, dosages ranged from 20-60 g/day. Folks, that’s a lot of glutamine! However, I believe that the recreational athlete could see positive results with 5-10 g/day and for the competitive athlete 5-20 g/day. I derived these discretionary numbers based on the research presented above. If 20 g of intravenous glutamine has been shown to have beneficial effects in patients with major trauma or injury, than I will assume that smaller oral doses will be sufficient for athletes.

There are numerous supplements sold that have glutamine added to them, and you can also find free-form L-glutamine. One word of caution though: An excessive intake of free-form L-Glutamine is not recommended if you have kidney or liver dysfunctions, such as cirrhosis or renal insufficiency. This is because supplementation with L-Glutamine under these conditions might lead to the accumulation of urea or ammonia. Also, L-Glutamine is only stable in a solution when heat sterilization techniques have not been employed.

However, even under this condition the glutamine is poorly soluble. Therefore, your best bet would be to purchase a product that has added glutamine or a dipeptide-glutamine mixture such as glutamine bound with alanine or glycine.

When in the dipeptide form, glutamine is absorbed much more readily (3).

Some supplements that contain glutamine mixed with other amino acids include Met-Rx and Experimental and Applied Sciences’ (EAS) meal replacement powders and nutrition bars; EAS’s Phosphagain 2, CytoVol, and GKG; TwinLab’s Anti-Catabolic Fuel and Rx-Fuel; and Next Nutrition, Inc.’s Designer Protein. Look for products that have glutamine listed as one of the first 5 protein ingredients. For instance, the meal replacement powders mentioned above meet this criterion. Since they contain around 35-42 g/protein per serving, you can be pretty confident that they have around 5-6 g/glutamine per serving.

This is more than a serving found in the glutamine solutions. (Of course, the 5-6 grams may vary because the companies will not tell you exactly how much glutamine is in their meal replacement powders - for obvious reasons.) So if you’re a recreational athlete aiming for 5-10g of glutamine per day, besides whole food sources, 1-2 servings of a meal replacement power would do the trick.

If you’re a competitive athlete, supplementing with a “cell-volumizing” solution such as CytoVol or GKG along with a meal replacement powder would be appropriate. Also, most whole food sources contain around 4-8% of their amino acid residues as glutamine (8) and therefore less than 12 gm of glutamine is likely to be consumed by the average athlete.

Based on recent research, it is clear that glutamine plays a crucial role in anticatabolism and anabolism. It also plays a strong role in the integrity of the immune system and intestinal flora. It is believed that these benefits occur from a cellular hydration state that accompanies optimal quantities of intracellular glutamine. If you are interested in increasing performance, muscle mass, or decreasing recovery time, give glutamine a try.
Who knows, it just may be that missing link you’ve been looking for. 

References

1. Bergström, J. V. Jr., Fürst, P., Noree, L.-O., & Vinnars, E. (1974).
Intracellular free amino acid concentration in human muscle tissue. Journal of Applied Physiology, 36, 693.
2. Ziegler, T. R., Smith, R. J., Byrne, T. A., & Wilmore, D. W. (1993). Potential role for glutamine supplementation in nutrition support. Clinical Nutrition, 12 (Suppl 1), S82.
3. Fürst, P. & Stehle, P. (1995). Glutamine and glutamine-containing dipeptides.
In L. A. Cynober (Ed.), Amino acid metabolism and therapy in health and nutritional disease (pp.373-383). Boca Raton: CRC Press.
4. Castell, L. M., Poortmans, J. R., & Newsholme, E. A. (1996). Does glutamine have a role in reducing infections in athletes? European Journal of Applied Physiology, 73 (5), 488-490.
5. Rowbottom, D. G., Keast, D., & Morton, A. R. (1996). The emerging role of glutamine as an indicator of exercise stress and overtraining. Sports Medicine, 21 (2), 80-97.
6. Haussinger, D., Roth, E., Lang, F. & Gerok, W. (1993). Cellular hydration state: an important determinant of protein catabolism in health and disease. Lancet, 341, 1330.
7. Scislowski, P. W. D., Niblock, A., Lindsay, Y., Weryk, B., Watt, P. W., &
Rennie, M. J. (1989). Glutamine stimulates glycogen synthesis in skeletal muscle. Clinical Nutrition, 8, 80 (abs.).
8. Souba, W. W. (1992). Glutamine physiology, biochemistry and nutrition in critical illness. Austin: R. G. Landes Company.
9. Millward, D. J., Jepson, M. M., & Omer, A. (1989). Muscle glutamine concentrations and protein turnover in vivo in malnutrition and endotoxemia. Metabolism, 38 (8), 6-13.