Glutamine is the most abundant amino acid in the body and is involved in more metabolic processes than any other amino acid.^{1 2 3} It is the preferred source of fuel for immune cells and the cells that line the gastrointestinal (GI) tract. Glutamine is essential for proper GI, immune, and muscle function. It also helps maintain the pH balance in our bodies, acts as a precursor to the neurotransmitters GABA and glutamate and the important antioxidant glutathione, and plays a role in the synthesis of DNA and RNA (and you thought amino acids were just the building blocks of protein!). It is considered a conditionally essential amino acid, meaning that under normal circumstances, the body can typically make enough glutamine for its regular needs; however, under stressful conditions, including intense exercise, serious illness, surgery, injury, or even malnutrition, the body’s reserves are rapidly depleted, making supplementation necessary. Additionally, because muscle tissue is the main place where glutamine is produced, people with low muscle mass, such as the elderly or those with muscle wasting diseases may be at risk for glutamine deficiency.⁴

Glutamine the “muscle food”

Whether your activity of choice is running, cycling, swimming, hiking, or skiing, your muscles can get a boost from glutamine. Our muscles get their energy from glycogen, the storage form of glucose and the body’s fuel of choice for physical activity. What does glutamine have to do with this? Glutamine helps replenish glycogen in the muscles after intense exercise⁵ and can be converted to glucose when the body has higher energy needs (e.g. during heavy exercise).⁶ High-intensity and endurance exercise depletes glutamine reserves,^{7 8 9} so supplementing becomes important. Additionally, intense physical exertion causes the body to release high levels of the catabolic hormone cortisol, which decreases glutamine stores and induces breakdown of muscle.^{10 11} Supplementing glutamine can help keep the body in an anabolic state (a state of repair and maintenance), making it easier to build and maintain muscle mass.^{12 13}

Glutamine and critical illness

While glutamine has become a favorite supplement among athletes and exercise enthusiasts, research is proving that it can also be beneficial to those who are critically ill. Clinical studies have demonstrated that glutamine supplementation (both orally and through a feeding tube) can be of benefit to seriously ill patients by maintaining the mucosal integrity of the gut; improving immune function; increasing levels of the protective antioxidant glutathione; and increasing muscle mass.^{14 15} One study involving 84 critically ill patients found that the patients receiving glutamine left both the intensive care unit and the hospital significantly sooner than the patients who did not receive glutamine.¹⁶ When given with radiation or chemotherapy, glutamine has a protective effect on the gut, the nerves, and other tissues.^{17 18 19 20 21 22} [Editor’s note: Glutamine is not a treatment for cancer and may be inappropriate for some types of cancer. It is crucial to work with your doctor if you have cancer and are considering taking glutamine.]

Glutamine and immune health

Glutamine is the main source of energy for certain immune cells, including macrophages (a type of white blood cell) and lymphocytes (T-cells and natural killer cells), and directly contributes to the proliferation of these cells. These cells cannot synthesize glutamine on their own and depend on other bodily tissues to provide glutamine. ^{23 24} When the body is under heavy stress (intense, prolonged exercise or training; critical illness; surgery; traumatic injury; viral or bacterial infections; or even general chronic stress) glutamine reserves are sometimes so severely depleted that immune cells starve. This may explain why overtrained athletes, seriously ill patients, and people who are chronically stressed tend to be more susceptible to infections. One study found that endurance athletes who supplemented with 5g of glutamine after exercise had a significant decrease in infections compared to athletes who didn’t (19% of the supplemented athletes and 51% of the unsupplemented ones got sick). Other controlled studies have shown that glutamine supplementation improved immune function in postoperative patients, increasing Tcell and IgA production (IgA is an antibody that plays a critical role in mucosal immunity), thus reducing the frequency of infections and decreasing the length of hospital stays.^{25 26 27} Glutamine is also a precursor to glutathione, a powerful antioxidant that also plays an important role in immune health.

Glutamine and gut health

Just as immune cells prefer glutamine as a major source of fuel, so do the cells that line the digestive tract (the mucosa). Glutamine maintains the structural integrity of the intestinal lining by preserving healthy permeability and protecting the villi that line the GI tract.²⁸ Glutamine is a regulator of intestinal tight junction barriers and a depletion of the amino acid leads to rapid increases in gut permeability. ²⁹ Increased gut permeability (leaky gut) can allow substances such as undigested food, toxins, and microbes to leak through the gut wall, which may contribute to the development of autoimmune diseases. Glutamine has also been shown to shorten the duration and accelerate mucosal healing and regeneration in people with diarrhea and colitis^{30 31 32} and to decrease intestinal permeability caused by long-term use of non-steroidal anti-inflammatory drugs (NSAIDs). ³³

Glutamine and Blood Sugar

Glutamine can serve as an emergency source of energy when blood levels of glucose fall too low. This can be particularly beneficial to the brain, which is exceptionally sensitive to fluctuations in blood sugar. Not only does it help to stabilize blood sugar but in doing so, it helps to minimize the cravings for sugar, carbohydrates and alcohol that tend to come when blood sugar drops.³⁴

Getting More Glutamine

Glutamine is widely available in animal and plant protein but is easily damaged by heat. One of the best sources of glutamine is raw cabbage (and red cabbage in particular), but raw beets, spinach, and parsley are also good sources.^{35 36} Common dosages for supplemental glutamine fall between 500-1,000 milligrams, three times daily between meals.³⁷ Supplemental glutamine should be used with caution by anyone with a condition that causes the accumulation of ammonia in the blood or by diabetics who tend to have abnormal glutamine metabolism.^{38 39} Amino acids are not often the first supplements that come to mind when thinking of important dietary supplements to keep on hand. However, glutamine is one amino acid that can benefit so many people in so many different ways. Don’t discount this “non-essential” amino acid that is actually quite essential for good health!

References Available Upon Request