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L-Glutamine | What Is It and What Does It Do? Benefits? Side Effects?

L-Glutamine is produced by the body and available in common foods, but is also a popular supplement due to its variety of potential health and performance benefits. Glutamine exists in two different forms, L-Glutamine and D-Glutamine, which only vary in molecular structure. For the purpose of this article, we will focus on the specific health benefits and side effects of L-Glutamine.

What is L-Glutamine?

L-Glutamine is an amino acid, or a building block of protein. Amino acids and proteins play many key roles in our body. It helps with transport of nitrogen (used for cell division and growth) and carbon in our bodies and plays roles in neural function, intestinal function, and boosting our immune system.2

L-Glutamine is made by the body in our muscle tissue and is therefore considered “non-essential” – meaning we don’t have to strictly consume it from our diet.1 However, when our body is under physical (metabolic) stress, it may require more glutamine than it makes on its own.2

This need for additional glutamine when our body is using it in higher amounts supports the argument that l-glutamine is actually “conditionally essential” – meaning there are times when it’s necessary to consume more than what our body produces.3

It makes sense that making our muscles work hard would demand more l-glutamine – since they’re responsible for producing it in the body. Metabolic stressors that make our body require more glutamine include both severe illness and intense exercise.

The fact that L-glutamine is made by our muscles, common in our diet, and circulates in our blood makes pinpointing its effects challenging, but it’s clear that it’s used by the body both during exercise and recovery from serious illness.1,5


Food Sources of L-Glutamine

Dietary sources of L-Glutamine include a variety of foods from animal foods like eggs and beef to vegetable sources like rice or corn.4 Due to this wide availability in food, following a healthy diet can provide adequate L-glutamine for most people. However, during exercise, L-glutamine production changes based on the type and intensity of exercise.5

Because L-glutamine is crucial for muscle building, increasing our levels via supplementation after exercise can be beneficial.5 Those who follow a lower protein diet (like vegans or vegetarians) may see a greater benefit from l-glutamine supplementation that someone who is already following a high protein diet (which may be naturally higher in l-glutamine).

Many sports supplements are targeted towards strength training, but l-glutamine has potential benefits for both power exercise and endurance exercise.5

Benefits of L-Glutamine

Quick Recovery

Research has shown that athletes can benefit from L-glutamine supplementation to decrease muscle soreness and faster recovery time.5

Glutamine plays a key role in controlling glucose (energy) uptake by the muscles after exercise, which can help restore their energy stores for your next workout.6 When your muscles have optimal glucose stores, you can perform better and take longer to fatigue.

Long periods of strenuous training have been shown to decrease blood glutamine levels, making glutamine potentially useful as part of your post-workout nutrition plan.1


Increased Lean Body Mass and Power

When combined with creatine, L-glutamine supplementation has been shown to increase lean body mass and power with endurance exercise.7 While supplemental L-glutamine might be more effective for those who have a diet low in glutamine, there are studies showing additional potential benefits like:

  • Limited strength loss and reduced muscle soreness8
  • Feeling less fatigued9
  • Longer time to exhaustion in endurance exercise9


Boost in Immunity

Additionally, athletes who follow intense training schedules tend to have weakened immune systems, due to the constant physical stress of high intensity exercise.

L-glutamine is actually used to help the immune system of critically ill patients in the hospital, due to its protective effect on cells in our immune system.10

Research shows that L-glutamine plays a role in both immune cell production (having enough to fight off germs) and the gut’s function as a physical barrier to infection.3 For these reasons there may be potential benefit to your immune system from an L-glutamine supplement as well.2

L-glutamine Dosage and Timing

Because glutamine has shown to be in lower concentrations after intense training sessions, it’s essential to take L-glutamine after your workout to help your muscles rebuild and grow.1

It can be taken on its own or as part of your post workout protein shake, since protein is another key for muscle recovery and building.1 L-glutamine’s role in controlling glucose (energy) usage during workouts means it can be useful to take it before a workout instead.6


Potential Side Effects of L-glutamine Supplementation

The only time when L-glutamine supplements might not be safe is for those with liver disease, or people taking anticonvulsants, or on chemotherapy.2,11 Glutamine is partially metabolized to ammonia, which can increase blood ammonia and blood glutamate levels in high doses.2

Studied doses of glutamine ranged from 5-28 grams per day, with a published observed safe level of a maximum of 14 grams per day, and no increase in plasma ammonia levels.1,2

Because L-glutamine is both made by the body and present in many foods we eat on a daily basis, there are limited potential side effects even when taking it every day. 1,2


Take Home Message

L-glutamine is an important amino acid that plays many roles in our body regardless of our level of exercise. However, the stress that exercise puts on our body can deplete our l-glutamine levels, making it a useful supplement for athletes.

It shows many potential benefits to performance, recovery, and body mass with limited side effects. It can also be useful to boost our immune system and help sustain adequate levels in those who follow low protein diets.

Our articles should be used for informational and educational purposes only and are not intended to be taken as medical advice. If you’re concerned, consult a health professional before taking dietary supplements or introducing any major changes to your diet.

  1. Gleeson, M. (2008). Dosing and efficacy of glutamine supplementation in human exercise and sport training. The Journal of nutrition138(10), 2045S-2049S.
  2. Operation Supplement Safety. (2019). Uniformed Sciences University Consortium for Health and Military Performance. Glutamine. Retrieved from https://www.opss.org/glutamine
  3. Hall, J. C., Heel, K., & McCauley, R. (1996). Glutamine. British Journal of Surgery83(3), 305-312.
  4. United States Department of Agriculture Agricultural Research Service. (2019, January 29). USDA Food Composition Databases Nutrient List. Retrieved from https://ndb.nal.usda.gov/


  1. Legault, Z., Bagnall, N., & Kimmerly, D. S. (2015). The influence of oral L-glutamine supplementation on muscle strength recovery and soreness following unilateral knee extension eccentric exercise. International journal of sport nutrition and exercise metabolism25(5), 417-426.
  2. Iwashita, S., Williams, P., Jabbour, K., Ueda, T., Kobayashi, H., Baier, S., & Flakoll, P. J. (2005). The impact of glutamine supplementation on glucose homeostasis during and after exercise. Journal of applied physiology.
  3. Lehmkuhl, M., Malone, M., Justice, B., Trone, G., Pistilli, E. D., Vinci, D., … & Haff, G. G. (2003). The effects of 8 weeks of creatine monohydrate and glutamine supplementation on body composition and performance measures. The Journal of Strength & Conditioning Research17(3), 425-438.
  4. Street, B., Byrne, C., & Eston, R. (2011). Glutamine supplementation in recovery from eccentric exercise attenuates strength loss and muscle soreness. Journal of Exercise Science & Fitness9(2), 116-122.
  5. McCormack, W. P., Hoffman, J. R., Pruna, G. J., Jajtner, A. R., Townsend, J. R., Stout, J. R., … & Fukuda, D. H. (2015). Effects of L-alanyl-L-glutamine ingestion on one-hour run performance. Journal of the American College of Nutrition34(6), 488-496.
  6. Melis, G. C., ter Wengel, N., Boelens, P. G., & van Leeuwen, P. A. (2004). Glutamine: recent developments in research on the clinical significance of glutamine. Current Opinion in Clinical Nutrition & Metabolic Care, 7(1), 59-70.
  7. Shao, A., & Hathcock, J. N. (2008). Risk assessment for the amino acids taurine, L-glutamine and L-arginine. Regulatory toxicology and pharmacology50(3), 376-399.

Claire Muszalski

Claire Muszalski

Registered Dietitian

Claire is a Registered Dietitian through the Academy of Nutrition and Dietetics and a board-certified Health and Wellness Coach through the International Consortium for Health and Wellness Coaching. She has a Bachelor of Science in Biology and a Master’s degree in Clinical Dietetics and Nutrition from the University of Pittsburgh.

Talking and writing about food and fitness is at the heart of Claire’s ethos as she loves to use her experience to help others meet their health and wellness goals.

Claire is also a certified indoor cycling instructor and loves the mental and physical boost she gets from regular runs and yoga classes. When she’s not keeping fit herself, she’s cheering on her hometown’s sports teams in Pittsburgh, or cooking for her family in the kitchen.

Find out more about Claire’s experience here.

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