For ATHLETIC PERFORMANCE, athletes turn to L-glutamine, a classic remedy to prevent muscle breakdown and to improve immune functioning. Glutamine stimulates muscle building and recovery, slows breakdown of tissue proteins, and is fuel for muscle cell division. It improves the formation of new protein, boosts metabolism and performance, and reduces infection risk. Research confirms that L-glutamine significantly helps to enhance athletic outcomes in multiple ways.

L-glutamine is an amino acid, a protein building block, that exists in two forms: D- and L-glutamine. The biologically important form is L-glutamine. The body naturally produces low levels of L-glutamine, but it is considered a “conditionally essential” amino acid because we use it in large amounts, and it can only be synthesized by some cell types under certain conditions. We cannot make the greater quantities needed for high-intensity athletic activity, or for times of stress or trauma to meet physiological demands, so we must ingest it.

L-glutamine is the most abundant amino acid in the human body, making up 30 to 35% of the amino acid nitrogen totals in the blood and other body fluids. Glutamine is a key molecule in new tissue formation, repair of injuries and energy production, and it contributes to many critical biochemical reactions. It also supports good blood circulation and perfusion of exercising muscles. After injury, the body cannot produce optimal amounts of glutamine, therefore supplementing can be beneficial for recovery and immune health. There is a robust body of evidence supporting the association between L-glutamine supplementation, and improved injury and wound healing.^7,8

L-glutamine is stored in muscles and released into the bloodstream when the body undergoes the physical stress of exercise. Glutamine is especially important during prolonged and intense physical exertion, such as long-distance running and high-intensity strength training. It is considered anabolic for skeletal muscle, meaning that it encourages muscle build up. Glutamine plays essential roles in pH regulation, maintaining a healthy alkaline-acid balance, and in gluconeogenesis, providing a steady glucose supply to exercising muscles. There is evidence that demanding athletic training depletes glutamine, and that glutamine supplementation boosts performance. It can also help prevent training injuries. In addition, glutamine provides fuel for immune and intestinal cells and helps keep the cell-to-cell connections in the intestines strong.

There are modest amounts of glutamine in a well-balanced diet that contains a variety of vegetables, nuts, and lean sources of protein, usually enough to meet the nutritional needs of an average sedentary or mildly active person. For example, a serving of egg, tofu or beef can provide about 500 mg. But athletes put greater demands on their body systems, creating increased L-glutamine needs that cannot be met through diet alone. Cooking can also destroy glutamine in certain foods, especially vegetables.

For immune support in athletes, L-glutamine is needed for formation of white blood cells, particularly by lymphocyte immune cells that use it at high rates for nucleotide biosynthesis and resulting cell proliferation. Insufficient glutamine can lead to fewer immune cells being produced in response to antigens, and an impaired immune defense to viral infection.⁶ Glutamine is also needed as a major fuel by cells of both the gut and the immune system.⁷

Studies on endurance athletes show that deficiency of L-glutamine is linked with inflammation, oxidative stress, and interruptions in immune system functioning, as well as reduced stamina and performance. Glutamine is a precursor for making the body’s “master antioxidant,” glutathione, which protects exercising tissues from oxidative injury. A 2017 review looked at the benefits of certain effective nutrients on immune support for the athlete. The cycles of physiological stress that athletes in training experience can affect cortisol and immune cell functions. The consequences include transient inflammation of joints or connective tissues or elevation of inflammatory mediators; increases of free radicals that can cause oxidative stress; and a higher risk of infections or autoimmune disease. Researchers noted that these effects can be mitigated by nutritional influences: L-glutamine appears especially valuable for reducing these risks.¹

L-glutamine can offset the increased risk of infections in athletes undertaking prolonged, strenuous training. There is evidence that after intense exercise cells of the immune system are less able to mount a defense against infections. Glutamine is a very important fuel for cells of the immune system, yet its plasma level decreases in athletes after endurance exercise. This may account for the depressed immune function in these individuals.

Researchers in a 1996 study monitored levels of infection in more than 200 runners and rowers. They noted that infection rates were highest in runners after full or ultra-marathons and in elite rowers after intensive training, and lowest in middle-distance runners. In this research study examining glutamine and immunity, athletes were divided into two groups. They received either glutamine or placebo immediately following exercise and again two hours later. The results indicated that the percentage of athletes who took L-glutamine had an 81% higher chance of reporting no infections than those who received the placebo.²

After an intense workout, cellular glutamine levels can drop by 50% and plasma levels by 30%. This would force the body to break down muscle for energy rather than carbohydrates. But a notable physiology study found that glutamine can help. Subjects completing an exercise protocol designed to deplete both type I and II muscle fibers of glycogen, received either glutamine or a control. Athletes who received glutamine maintained better muscle mass by preventing protein breakdown. They also improved their glycogen synthesis, thereby increasing muscle glycogen stores.³ This means that by rebuilding their carbohydrate energy stores, and through better use of carbohydrate as fuel, they suffered less protein loss from muscles.

A 2015 sports nutrition study compared the effect of glutamine versus placebo on recovery from exercise consisting of unilateral knee extensions in 16 young adult men and women. Supplementation with glutamine reduced the magnitude of strength loss after exertion and decreased the weakening of muscles, accelerated strength recovery, and diminished muscle soreness more quickly than placebo. These effects were more pronounced in the men.⁴

In our clinic, our active patients taking L-glutamine regularly note more efficient muscle building, and more sustained strength during exercise repetitions. They also comment on less muscular aching after training, and faster recovery. Some patients who take L-glutamine are reporting fewer seasonal respiratory infections.

Recommendation: L-glutamine 1,000 to 2,000 mg. daily total, with any meals, from a vegan source, or as directed by your healthcare provider.

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