Glutamine: Does Supplementation Benefit?

Glutamine—the latest hype. Athletes you work with may be asking you about this “new” supplement. Glutamine, an amino acid found in high concentrations in animal proteins, is believed to improve the immune system and prevent the loss of muscle mass.But what do we know about this amino acid?

Multiple Roles of Glutamine

Glutamine is the most abundant amino acid in plasma as well as skeletal muscle. It accounts for more than 60% of the total intramuscular free amino acid pool.

It is generally referred to as a non-essential amino acid because the body’s skeletal muscle and adipose tissue can produce most of what the body needs.

However, recent evidence supports the idea that glutamine is a “conditionally essential” amino acid. For example, under conditions of severe stress, the amount of glutamine the body produces is insufficient to meet the demands of the body.

The varied roles of glutamine in the body include acting as a carrier, a buffer, a substrate for cell synthesis, and a fuel source. Glutamine is a major fuel of the gastrointestinal tract, especially during fasting. The GI tract accounts for 40% of the total gluatmine used by the body. Glutamine is also used by the GI tract to maintain protein synthesis required by the high turnover rate of entrocytes.

Glutamine is also a fuel source for cells of the immune system and hair follicles. During fasting and metabolic acidosis, glutamine is used as a fuel source by the kidneys to support renal ammoniagenesis. Glutamine is also used for glucose and urea synthesis in the liver, while in the brain glutamine is used as a precursor for neurotransmitter substances. During metabolic acidosis, glutamine is converted to a-ketogluterate, thus generating ammonium ions (NH4+).

The excretion of ammonium ions helps buffer the acidotic condition. Additional roles of glutamine that may be relevant to active individuals are its function in glycogen replenishment after exercise and its antibiotic effect with respect to skeletal muscle.

Supplementation in the Critically Ill

Glutamine supplementation is not new. Human experiments with glutamine supplementation began over ten years ago, primarily in critically ill patients. Studies of patients undergoing abdominal surgery and /or gallbladder removal suggest that glutamine supplementation improved nitrogen balance and improved protein synthesis. Although these studies suggest benefits of glutamine supplementation to certain populations, it may not be relevant to the healthy athlete.

Implications for Athletes

Research indicates that levels of glutamine fall after exhaustive exercise. One theory is that a shortage of glutamine is partially responsible for the increased frequency of illness observed in athletes during periods of heavy training and after endurance competitions. If feeding the body more glutamine to meet the needs in times of heavy endurance training and competition would strengthen the immune system; frequency of illness could be decreased.

In a study conducted on glutamine consumption, athletes consumed glutamine immediately and 2 hours after a marathon and ultramarathon. This reduced the incidence of infections during the week after competition by 32% when compared to the placebo.

However, in a follow-up study, researchers were unable to show a positive effect of glutamine on immune function in a group of marathon runners. Current evidence also indicates that adequate glutamine aids the immune system in times of stress. Whether the glutamine needs to be provided in supplement form or provided through an adequate diet remains unanswered.

Glutamine may also function in the preservation of muscle tissue, but there is little evidence to support this claim as well. At this time there is no evidence to support that supplementation will enhance body composition or exercise performance in weight –training athletes.

Diet vs. Supplementation

Animal proteins are rich in glutamine. Therefore, athletes consuming high-protein, high-calorie diets would be the least likely to need glutamine supplementation. Athletes who would be at risk for inadequate glutamine would be those who are competing in endurance events, such as distance running and cycling, and those who do not have adequate intake of calories, carbohydrates, or protein. Glutamine is absorbed efficiently by the intestine when present in the diet.

The value of adequate glutamine in the body is undisputed. What remains unanswered is whether supplementing with glutamine will produce beneficial outcomes for athletes. There has been little research to support any beneficial claims to athletic performance.

Source Content:

Article by Debbi Whitcombe M.S. RD Reference: SCAN’s Pulse, Spring 2000; Vol. 19 No. 2

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