Glutamine is the most abundant amino acid in the body accounting for greater than 60% of the total intramuscular free amino acid pool. Practically every cell in the body uses this non-essential amino acid. Glutamine is synthesized in both skeletal muscle and in adipose tissue in addition to the lungs, liver and brain.
Because the body has the ability to produce glutamine it has long been considered a non-essentials amino acid. But don’t let the word non-essential throw you off. Non-Essential simply means the body has a mechanism to produce this powerful amino acid. Some scientists have recently considered reclassifying glutamine as a conditionally essential nutrient based on recent research findings.
There is evidence that during times of stress the body cannot produce enough glutamine to keep up with demand which in-turn can reduce performance, immune function and affect mood. Hence glutamine is now classified as a conditional non-essential amino acid. Athletes at risk for inadequate stores of glutamine include those not eating enough calories, carbohydrates or protein or those participating in strenuous endurance events. The need for proper daily eating is important to help maintain normal glutamine levels. Additionally, clinical research has verified that overtrained endurance athletes suffer from chronic low plasma glutamine levels.
Intense physical exercise drains Glutamine stores faster than the body can replenish them. When this occurs, the body breaks down muscles and becomes catabolic. Clinical evidence supports supplementation with glutamine for recovery, glycogen storage & transport, synthesis of other amino acids and to reduce the catabolic effects of overtraining. Its been proven that glutamine levels in the serum are dramatically reduced following exhaustive exercise. With reduced glutamine levels performance and recovery are also compromised.
Conditions of severe stress such as exposure to extreme altitude, massive trauma, and burns have been shown to decrease glutamine concentrations similar to the reductions noted in endurance athletes after training and competition. Supplementation with glutamine has been shown to improve recovery rates in these patients, and has also been linked to improve gut function. The evidence for maintenance of healthy immune function is one more great benefit to glutamine supplementation.
A strict and strenuous training program, which does not allow for enough time to recover, may cause an athlete to experience overtraining syndrome (OTS). Researchers have effectively correlated OTS to amino acid imbalances. Decreased performance, decreased mood, and increased incidence of infections characterize these amino acid imbalances caused by OTS. Significantly decreased plasma glutamine concentrations have been observed after prolonged exercise in healthy athletes as well.
Athletes who exercise extensively and are suffering from OTS may become immuno-suppressed leading to infection and increased upper respiratory tract infections (URTI). Supplementing with glutamine in order to maintain normal levels of intramuscular glutamine is critical in maintaining a strong immune system AND preventing the breakdown of skeletal muscle and catabolism (the breakdown of muscle).
Supplementation vs Foods: Most naturally occurring food proteins contain only 4 to 8% of their amino acid as glutamine. Though glutamine is available in small quantities from a variety of foods, such as cabbage, beets, beef, chicken, fish, beans and dairy products, it is easily destroyed by cooking. Raw vegetables can be a good source of glutamine though evidence suggests that dietary glutamine is not easily absorbed through the intestine. On the contrary a stable form of glutamine from dietary supplements has a better absorption rate.
Glutamine and Endurance Performance: Glutamine supplementation is most effective during those times of high-volume and/or high intensity training, particularly if you are in danger of OTS. Though glutamine may not offer a direct ergogenic performance enhancing effect, it will offer insurance for the maintenance of skeletal muscle and immune function. It’s anti-catabolic and immuno-stimulant properties are critical during times of heavy training. There is also evidence supporting the use of glutamine to enhance glucose replenishment. Using glutamine in conjunction with carbohydrates and proteins further improves glycogen resynthesis. Sustaining adequate glutamine levels may also help modulate the damaging effects of cortisol (see cortisol newsletter). Supplementation with 6-8 grams/day of BCAA and glutamine has been shown to decrease protein degradation during ultra-distance triathlon competition, decrease exercise induced muscle damage after prolonged running, and improve 40K cycling time trial performance.
Recommendation: Several research studies have reported that overtrained athletes have lower plasma glutamine concentrations than non-overtrained controls. A review of the literature recommends supplementing with free form glutamine from 4g to 40g per day. Though 40g per day is impractical and just too expensive, 5g to 10g daily may be adequate. For maximum results pay special attention to supplementing with glutamine immediately following long exhaustive exercise. Athletes who consistently use glutamine through their race season will experience improved energy, improved recovery, improved nitrogen balance and reduced incidence of infection.