What are the active ingredients of L-Glutamine, and what are its effects on the body?
I have chosen to include an excerpt from the book An Evaluation of Popular Fitness-Enhancing Supplements by Neal Spruce and Alan Titchenal, Ph.D. to explain glutamine and its many contributions to the exerciser.
L-glutamine,the most abundant amino acid in the human body, has a unique structure and importance to the intense exerciser. L-Glutamine is commonly used to potentially enhance hypertrophy (muscle size).
Role of L-Glutamine
Glutamine contains two nitrogen radicals, which enable its use in numerous important biochemical reactions involving transaminations and deaminations. Glutamine also is categorized as a conditionally essential amino acid because its needs are met during low activity and low physical stress. However, as activity levels and physical stress increase, glutamine levels begin to decline and output exceeds intake significantly. This allows glutamine to have many potential applications of importance to the exercising population, including the following: regulating protein synthesis, acting as an anticatabolic, contributing to glycogen storage after exercise, buffering blood pH and contributing to immune and gut cell functioning.
Glutamine and Protein Synthesis
The relationship between glutamine’s intramuscular levels and protein synthesis is important because glutamine is in greater amounts than any other free amino acid in the human skeletal muscle. Animal and human studies have shown a positive correlation between intramuscular levels of glutamine and protein synthesis. Studies have also shown that stressful conditions - such as surgery, sepsis, glucocorticoid administration and exercise - decrease the intramuscular glutamine concentrations.
The decrease in intramuscular glutamine is due to an increase in its synthesis within muscle and associated with increased export from muscle to the blood. Rapidly dividing cells such as enterocytes and immunocytes are the recipients. Enterocytes are cells in the digestive tract; immunocytes are cells in the immune system.
Since stress exerts a catabolic effect, the decrease in intramuscular levels of glutamine may be the biochemical mechanism responsible for the resultant loss in lean body mass (LBM). LBM, also called >fat-free mass (FFM), refers to all portions of the body not containing fat, such as the skeletal bones, muscles, skin, hair, blood and lymph.
Glutamine levels decrease in proportion to stress, with levels decreasing by more than 50 percent under some conditions. Based on this knowledge, glutamine is typically used to inhibit protein loss by improving nitrogen retention and increasing protein synthesis. Following surgery, patients who receive supplemental glutamine, tend to recover more quickly, have fewer complications and lose less LBM than those who do not receive glutamine supplementation.
Glutamine and Glycogen Accumulation
Another possible benefit of glutamine supplementation is the ability to promote muscle glycogen accumulation following exercise. In studies of rats in anabolic conditions, glutamine was found to stimulate hepatic glycogen synthesis. This was probably due to the enhanced activation of glycogen synthase from the stimulation of glycogen synthase phosphatase activity.
A 1995 study examined the ability of glutamine supplementation to increase glycogen accumulation after strenuous human exercise. The researchers found that infusion of glutamine in the recovery phase leads to a rapid increase in muscle glycogen concentration during the first hour of infusion. Their results suggest that glutamine is converted to glycogen within the muscle, and it possibly inhibits glycogen breakdown. This is consistent with the findings of rats in anabolic conditions, described in the previous paragraph.
Other Roles of Glutamine
Glutamine is also an important fuel source for the cells of the digestive tract (enterocytes) and the immune system (immunocytes), some of the most rapidly dividing cells of the body. Enterocytes absorb digested food and transport nutrients to the portal blood stream, where they are transported to the liver and subsequently distributed throughout the body. The presence of food in the digestive tract stimulates enterocyte production. Glutamine is the fuel source to feed this growth.
When stress decreases glutamine levels, it has a tremendous impact during illness or injury. The effects of illness occur earlier and to the greater degree in the intestines than any other organ in the body. Glutamine supplementation can help feed the gut, reducing the amount of glutamine removed from muscle and preventing loss of LBM.
Glutamine is also essential for the growth of immunocytes, especially lymphocytes, which grow rapidly when called on to rid the body of foreign substances. Many studies have confirmed glutamine’s role in enhancing the immune function, decreasing infection following injury or trauma and improving rate of recovery.
Glutamine also plays a role in maintaining proper pH levels in the body, by clearing ammonia from blood and tissues.
Rationale for Glutamine Supplementation
When reviewing the findings on glutamine, supplementation seems justified for resistance training and other intense activities to reduce the catabolic effects of intense exercise. Glutamine supplementation would increase the body’s total glutamine pool, thus reducing the release from muscle, which normally occurs during exercise-induced stress. The subsequent higher levels of intramuscular glutamine could decrease protein loss and concurrently enhance its synthesis compared to the non-supplemented state. This may afford athletes faster recovery and less illness during heavy training (such as pre-competition).
Glutamine supplementation is probably of most interest to bodybuilders during pre-contest training when calories are severely restricted relative to energy expenditure, training is intense, and the immune system is compromised. Glutamine would push the cortisol-to-testosterone ratio in a more favorable direction. (Testosterone is a hormone produced primarily by the testes in the male, responsible for male secondary characteristics: the masculinization of boys to men and the primary reason that men carry more muscle than women.)
Finally, research suggests that glutamine supplementation may afford athletes optimal functioning over a greater period of time and thus a greater performance lifespan due to optimal functioning of the digestive tract. This would ensure maximal absorption and utilization of ingested food and nutrients and favourable immune function.
Many positive studies on glutamine supplementation have examined its impact on health and therapy, leading to the rationale for use by physically stressed athletes. However, few studies have shown glutamine’s efficacy for hypertrophy, strength or performance athletes. Currently, glutamine may be a safe and viable option for intense exercisers.
Typical Glutamine Dosages
Typical dosages, extrapolated from studies that suggest benefit and indicate safety, include the following: ü 2 to 20 g/d.
An Evaluation of Popular Fitness-Enhancing Supplements by Neal Spruce and Alan Titchenal provides a comprehensive overview of popular supplements used by individuals to alter body composition (i.e., lose fat, increase muscle) and enhance performance. Specific studies are presented regarding safety and effectiveness for the following supplement categories:
- Health enhancing
- Appetite control
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