Glutamine, or L-glutamine, is one of 20 essential amino acids the body needs to grow and function properly. It is used by almost every system and cell in the body in one way or another. It helps boost the immune system, strengthen the intestinal lining, increase brain function, and build and retain muscle.
It’s no wonder glutamine has been so popular with athletes for decades now and more recently has gained momentum in the medical world and with general health advocates. Let’s take a deep dive into some of the many benefits glutamine has to offer both athletes and non-athletes alike.
Glutamine as a Nonessential and Conditionally Essential Amino Acid
There are three classifications of amino acids: essential, nonessential, and conditional amino acids. (1) Nonessential amino acids are ones that are required for health and growth that your body can produce on its own. Of the 20 amino acids, 9 are considered nonessential: alanine, asparagine, aspartic acid, cystine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. In typical situations, with a standard healthy diet, nonessential amino acids are always available for your body to use.
Essential amino acids are amino acids that you need to get from the foods you eat. They include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The best sources for amino acids are animal proteins like fish, meat, dairy, and eggs. But, plants like soy, quinoa, and buckwheat also contain complete essential amino acids profiles. Without essential amino acids, your body would have a hard time making the protein that you need for repair and recovery.
Glutamine falls into the conditionally essential amino acid camp. In standard situations, it is nonessential, which is why it is listed above. Your body can create enough of it from a conventional diet, as long as it is rich in animal proteins and vegetables. However, glutamine is depleted during periods of high metabolic stress, severe illnesses like cancer, or after surgery. (2) In those cases, your body uses more glutamine than it can produce, and it needs to get more from other sources. This is what makes it conditionally essential.
Your skeletal muscle and your liver make L-glutamine. It is stored in your muscles and is released into the bloodstream when needed. Of the twenty amino acids, glutamine is the most abundant in your plasma and tissues. It serves as a quick energy source for your cells during periods of stress. Your kidney, liver, small intestine, and the cells of your immune system all use and need glutamine. (3)
Glutamine is essential for your intestinal health and your immune system. Athletes who take L-glutamine supplements generally do so to inhibit muscle breakdown and improve their immune system after intense exercise. While it may have advantages for some people, it may not be necessary for others.
Glutamine & Your Immune System
Glutamine improves your immune system. Supplements of glutamine are frequently given to people suffering from critical illnesses and recovering from major surgeries. Studies show that it can help reduce the rate of infectious diseases acquired during hospital stays and helps reduce the length of stay in a hospital. It has also been shown to decrease mortality in patients. (4) There are several ways that glutamine helps your immune system do its job.
Your body uses L-glutamine during times of stress, like an extended illness or recuperation after major surgery. Stress can also be prolonged and demanding physical exercise. Marathons, triathlons, or lengthy, high-intensity strength workouts like a CrossFit competition would all fit this definition. Glutamine levels in the plasma drop during these kinds of arduous events. However, studies show no change in the plasma glutamine during short-term exercise. The length and intensity of the illness or physical activity seem to be the key. (5)
Your immune cells use glutamine as fuel. Studies show that a glutamine supplement after strenuous exercise can improve an athlete's immunity. (6) Athletes who regularly get colds or flu during the week after a competition or race should make sure they are eating a balanced diet with natural glutamine. They may also benefit from glutamine supplementation to help boost their immune system.
There is another athlete with chronically low glutamine concentrations - the over-trained athlete. Scientists have found that chronically fatigued, over-worked athletes had a difference of 9% lower glutamine levels than that of healthy athletes. (7) This may be one of the reasons that over-trained, exhausted athletes frequently become ill. Illness and inflammation are ways that your body forces rest and restoration of glutamine levels. While proper rest and recovery are the best keys to stay healthy, glutamine can help in the short term.
Glutamine & The Intestine
Animal studies show that the inclusion of glutamine in the diet increases survival to bacteria challenges. (8) As with immune cells, it also serves as a source of energy for the mucosal epithelial cells in the gut. (9) This is why glutamine is an essential nutrient in maintaining the integrity of the gut barrier. A healthy gut barrier helps decrease the condition known as "leaky gut." Leaky gut occurs when there are holes or weak areas in the intestinal lining. Then food particles, bacteria, and toxins can all leak through the wall of the gut into the bloodstream. When the gut barrier is weakened, it leads to problems like irritable bowel syndrome and other GI illnesses.
Glutamine & Brain Function
Glutamine is a substrate for the generation of both excitatory and inhibitory neurotransmitters, (glutamate and gamma-aminobutyric acid, also known as GABA.) They are essential amino acids for brain metabolism and function. (10) Glutamine is found in plentiful supply in your central nervous system (CNS). The central nervous system consists of your brain and the spinal cord. The spinal cord is attached to your brain at the brainstem and runs through the spinal canal. Your spinal cord carries messages back and forth between your brain and your nerves. Cerebrospinal fluid surrounds the brain and the spinal cord and also circulates within the cavities (called ventricles) of the central nervous system.
There is more glutamine in your CNS than any other amino acid. Glutamine is the only amino acid that is capable of readily crossing from blood to the brain. And with glutamic acid, is thought to account for about 80 percent of the amino nitrogen of brain tissue. It is used as fuel and organizes the communication between cells of the brain and neurons. (11) This is why glutamine is sometimes used to improve memory and cognition.
Glutamine & Your Muscles
Glutamine has other benefits. There is a reason it has been a favorite supplement of athletes and bodybuilders for decades. It reduces time for muscle healing and repair. When you exercise, you damage your muscle at the cellular level. This may cause temporary diminished muscle function and short term soreness known as delayed-onset muscle soreness (DOMs.) You notice it the most when you are doing a particular activity for the first time, especially when eccentric high-force muscles are involved. But it is also noticeable after endurance events, like long-distance running. (12)
Inflammation is your body's way of repairing muscles. Messenger proteins will expand the small blood vessels around the damaged area and flood it with blood to remove toxins and begin the healing process. This is why an inflamed area might be red and feel warm. The same hormones that cause your blood vessels to expand irritate the nearby nerve endings. This is your body's way of forcing you to rest those muscles while they are under repair. With widened blood vessels, more blood, fluid, and proteins can access and enter the injured tissues in the area to start the healing process. This is what causes swelling.
It's all part of the strength-building process; however, glutamine is effective in reducing these symptoms. Plasma glutamine levels drop as much as 20-30% during extreme stress like prolonged, strenuous exercise. (Prolonged in this context means longer than 2 hours.) (12) Glutamine is needed to form the proteins that make up your muscles, so this is part of the reason that recovery from endurance events can be lengthy. With low reserves of glutamine, the muscles do not have enough to rebuild and repair. This is why a glutamine supplement can be beneficial. There is evidence that glutamine both stimulates protein creation and represses protein degradation. (13)
A supplement may also restore your glutamine levels and reduce inflammation. In fact, studies have shown that a glutamine supplement immediately after exercise resulted in significantly less strength loss and muscle soreness. (12) As mentioned, glutamine supplies nitrogen to muscules to manufacture proteins. This prevents muscle breakdown, so more muscle is retained, and more muscle is built. This also may be one of the reasons glutamine is effective in reducing fat levels and waist circumference. More lean muscle helps burn more calories and reduce fat.
Glutamine For Weight Loss
Studies show that glutamine decreases insulin levels. (14) Insulin is a hormone that is necessary for overall health. It's how cells use the sugar in your bloodstream for energy. However, too much insulin leads to severe diseases like diabetes, heart disease, cancer, and obesity.
In fact, glutamine has been shown to reduce the waist circumference in obese women, even without other lifestyle changes like exercise or diet. (15) One of the leading causes of disease is having fat around your organs. In studies with patients with heart failure and type 2 diabetes, glutamine supplementation helped reduce body fat and increase lean body mass. Glutamine supplements can improve fasting blood glucose, reduce body fat and waist circumference, and reduce body weight. (16)
Side Effects of Glutamine
Though glutamine is generally considered safe, some populations should avoid glutamine supplementation. People who have kidney or liver disease should avoid this supplement. Also, some people have had allergic reactions to L-glutamine. Allergic reactions may include joint pain, nausea, vomiting, or hives. Anyone who experiences these reactions should discontinue taking glutamine.
Do You Need a Glutamine Supplement?
Glutamine can be ingested through diet. It can be found in plants like beets, carrots, cabbage, and radishes as well as protein sources like beef, chicken, fish, and eggs. If you are eating a healthy, diverse diet, you are probably supplying your body with all the L-glutamine it needs for day-to-day living and short term exercise.
Supplementation makes sense for people dealing with long-term illnesses or recovering from surgery or trauma. It can help these patients fight off hospital-borne diseases and have a quicker recovery. Because of its ability to assist in muscle building, it can be especially helpful for patients dealing with wasting diseases like cancer or AIDs as well as burn victims.
Glutamine supplements can also be beneficial for athletes who compete in long, strenuous events or have extended training sessions. For those athletes, glutamine can help them build and maintain muscle mass. Because it can help the immune system build and repair cells, it can also be an asset for athletes who find themselves regularly getting ill in the five to seven days following an event. Athletes who are suffering from overtraining may also benefit from glutamine supplementation along with plenty of rest and recovery.
Sources:(1) Amino Acids https://medlineplus.gov/ency/article/002222.htm
(2) Integrative Medicine, 4th Edition, 2018 by Dr. David Rakel
(3) Glutamine and the immune system https://www.clinicalnutritionjournal.com/article/0261-5614(94)90003-5/fulltext
(4) Therapeutic benefits of glutamine: An umbrella review of meta-analyses
(5) Effects of Exercise Intensity, Duration and Recovery on in vitro Neutrophil Function in Male Athletes
(6) Does glutamine have a role in reducing infections in athletes?
(7) Plasma glutamine and upper respiratory tract infection during intensified training in swimmers. https://europepmc.org/abstract/med/8776216
(8) Glutamine and the immune system.
(9) Role of Glutamine in Protection of Intestinal Epithelial Tight Junctions
(10)Relationships between glutamine, glutamate, and GABA in nerve endings under Pb-toxicity conditions https://www.sciencedirect.com/science/article/pii/S0162013404000467?via%3Dihub
(11)Glutamine in the central nervous system: function and dysfunction.
(12) Glutamine Supplementation in Recovery From Eccentric Exercise Attenuates Strength Loss and Muscle Soreness https://www.sciencedirect.com/science/article/pii/S1728869X12600070
(13) Glutamine nutrition and requirements. https://www.ncbi.nlm.nih.gov/pubmed/2119461
(14) Evaluation of a novel food composition database that includes glutamine and other amino acids derived from gene sequencing data 'https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249386/
(15) Glutamine supplementation favors weight loss in nondieting obese female patients. A pilot study. https://www.ncbi.nlm.nih.gov/pubmed/25226827
(16) Oral Glutamine Supplementation Reduces Obesity, Pro-Inflammatory Markers, and Improves Insulin Sensitivity in DIO Wistar Rats and Reduces Waist Circumference in Overweight and Obese Humans