Increased Strength, Recovery, Immune Support, and Sports Performance with Glutamine
Glutamine supplements have been on the market since the 1990s. There has been great debate and discussion as to the effects of this supplement on human performance. Glutamine has commonly been known to aid athletes in several key forms. First, many believe that glutamine can play a considerable role in supporting a healthy immune function. This is especially true in athletes who may have a tendency to overtrain. This is of great importance as most athletes throughout the year can easily overtrain which often leads to sickness and a significant decrease in performance. Many companies also claim that glutamine aids in the storage and production of glycogen. This can be of key importance to most endurance athletes as well as to a high number of endurance oriented anaerobic athletes. Lastly, glutamine has been known for its anabolic effects of enhancing strength and muscle mass. It is often known around the bodybuilding world as a highly anabolic substance that greatly reduces catabolism and protein degradation. Many theories also advocate that glutamine may play a role in promoting an advantageous environment for heightened levels of growth hormone during intense levels of exercise.
Although the research is somewhat split around the supplementation of glutamine and its positive effects, there are many studies which show conclusive evidence pertaining to the effectiveness of orally ingesting glutamine. In a study performed by Welbourne et al (1), subjects who orally ingested only 2 grams of glutamine increased plasma bicarbonate levels in the body. Increased levels of plasma bicarbonate have been shown to improve one's ability to buffer lactic acid thus, increasing performance.
One of the most profound studies (2) performed on glutamine dealt with a very unique muscle regulator known as myostatin which is commonly produced by glucocorticoids. This substance may be one of the key factors that helps determine one's genetic potential for gaining muscle mass and strength. Specifically, moderate to high levels of myostatin may cause glucocorticoid muscle atrophy in healthy humans. In this specific study performed by Salehian et al (2), glutamine was found to prevent glucocorticoid induced muscle atrophy. In other words, this study showed that administration of glutamine provided a potential mechanism for the prevention of muscle atrophy induced by glucocorticoids and myostatin. Also, those who received glutamine had significantly less reductions in body and muscle weights and lower myostatin expression than the placebo group.
In a study by Lacey et al (3), short-term glutamine ingestion had no effect on muscular strength; however, long-term supplementation showed to be a more effective application of glutamine in regards to strength gains. Furthermore, other studies have shown that glutamine causes positive effects on performance due to a plethora of physiological events which include increased levels of growth hormone, decreased catabolic effects of skeletal muscle, increased anabolic effects, enhanced protein synthesis, and greater ability to sustain high intensity exercise due to the increased capability of buffering lactic acid.
Glutamine has also been shown to dramatically enhance immune system function for athletes and healthy adults who train at high enough intensities that typically trigger a breakdown in the immune system (4). From the medical literature, glutamine may have a place in the dietary regimen of athletes undergoing intense exercise training and possibly have a role in maintaining optimal health during the competitive season via benefits to the immune system (5).
Glutamine's effect on the immune system may also be witnessed by examining data on hospital patients supplementing glutamine in order to ward off any potential sicknesses associated with surgery or hospital stays. In a very recent study performed by Oquz et al (10), patients undergoing colorectal surgery for cancer were observed over a five year period. Half of the patients received glutamine treatment within their nutrition during their hospital stay and the other half did not. After results were analyzed, it appeared as though the group which received glutamine supplementation had less complications after their operation and a shorter hospital stay than those who were not administered the glutamine supplementation.
Many other studies also support glutamines use on immune system function, although not directly related to athletes. In a study performed by Fuentes et al (11), glutamine supplementation appears to improve infectious morbidity of hospitalized patients by improving host defenses and other immune system responses. In another study performed by Li et al (12), it appears as though premature infants given intravenous glutamine supplementation spend fewer days in the hospital and also have a decreased rate of hospital related infections.
Although many studies on glutamine supplementation and immune response are not performed directly on athletes, this does not suggest that these findings cannot be of great importance to athletes. In fact, exercise in and of itself can be a mild to somewhat intense form of stress and trauma on the body which may heavily tax the immune system. Although not as severe as surgical procedures performed on hospitalized patients, athletes undergoing intense training may find that glutamine does have a positive effect on immune system function.
As previously mentioned, there is an increased risk of infections in athletes undertaking prolonged, strenuous exercise. There is also some evidence that cells of the immune system are less capable of producing a defense against infections after such exercise. The level of plasma glutamine, an important fuel for cells of the immune system, is decreased in athletes after endurance exercise. This may be partly responsible for the apparent immuno-suppression which occurs in these individuals. In one of the more conclusive studies done on glutamine by Castell et al (7), oral consumption of glutamine after intense exercise was examined in elite runners and rowers. Most of these athletes were endurance oriented. The results of the study indicate that there was a significant decrease in infections and illness after intense training in those who supplemented with glutamine versus those who did not. Glutamine's role in enhancing immune system function seems to be highly conclusive in this study.
Candow et al (6) assessed the effect of oral glutamine supplementation combined with resistance training in young adults. Strength and muscular skeletal markers were examined before and after the six week study in both the placebo and experimental group. It appears as though there was a slight increase in one repetition squat, force production in the knee extensor, and lean muscle mass. Although these numbers were slightly higher than the placebo group, they were not enough to be a "significant" difference. It must be noted that many world class athletes may work years for small increases in performance that may or may not seem "significant" to those in a laboratory setting but may be of utmost importance to the elite athlete. However, to the average weightlifter, results from this specific study may not warrant supplementation with glutamine.
In regards to the proper and effective dosage of glutamine, research is quite varied. Some researches such as Van Gammeren et al (8) have shown success with as low as 2 grams of glutamine per day. While yet, other scientists such as Candow et al (6) administered substantially greater levels of glutamine to their subjects with as much as 45 grams of glutamine per day. However, the majority of studies as noted by Hultman et al (9) suggest that 4-10 grams per day will suffice for optimal physiological gains from glutamine supplementation. Yet, there are a host of others that would suggest up to 20 grams per day. The most extreme levels of glutamine supplementation can be seen in studies dealing with hospitalized patients. In fact, in the study performed by Oquz et al (10), patients received 1g/kg/day, which could be anywhere between 50-120 grams per day depending on body weight. It also appears from the previously mentioned studies that glutamine supplementation is far more effective when used long term rather than short term.
Summary and Recommendation
Although further evidence would help support supplementation with glutamine to an even higher degree, there is considerable research to warrant its usage among many high performance athletes. The benefits as previously noted includes: supporting a healthy immune system, less reduction in body and muscle weights, lower myostatin expression, increased levels of growth hormone, decreased catabolic effects of skeletal muscle, increased anabolic effects, increased protein synthesis, and greater ability to sustain high intensity exercise due to the increased capability of buffering lactic acid. All these factors could potentially lead to increases in muscle mass, strength, and power.
The recommended dosage for glutamine is 5-20 grams per day. There are claims that even higher dosages may be more effective, but further evidence is needed. However, there have been studies demonstrating that 40 grams a day has no safety or toxicity concerns. Therefore, toxicity is not an issue with glutamine supplementation. Distributing glutamine throughout the day in smaller dosages is also recommended. A common glutamine supplementation protocol is 5 grams in the morning, 5 grams pre-workout, followed by 5 grams post workout, with an optional 2-5 gram dosage before bed. Similar guidelines and dosage amounts are recommended for non-workout days.
According to consumerlab.com and other valid sources, some of the best glutamine products on the market include: Dymatize Proline Micronized Glutamine, Effervescent Glutamine, Puritan's Pride L-Glutamine, AST Glutamine, Beverly International Glutamine Select Plus BCAAs, and Precision Engineered Pure L-Glutamine.
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