What is L-Glutamine (L-Glutamine)?
L-glutamine is the most abundant free amino acid in the body, found in the highest concentrations in blood and muscle tissue. It is considered 'conditionally essential' because it is sufficiently synthesized in healthy individuals; however, needs may increase during intense stress, trauma, or heavy training. It is an important fuel and nitrogen source for intestinal epithelial cells and immune cells.
- CAS number: 56-85-9
- Molecular formula: C₅H₁₀N₂O₃
What is L-Glutamine Used For? Why is it Used?
L-glutamine is preferred in sports recovery and clinical nutrition products because it is an important substrate for intestinal epithelium and immune cells. There is randomized evidence supporting its acute use for intestinal integrity during strenuous exercise in the heat; however, benefits on performance and immunity are inconsistent and should not be presented as 'definite' honestly.
Usage as a Sports Nutrition Product
The following information is based on sports nutrition research (ISSN position stands, randomized controlled trials, and meta-analyses); the level of evidence is clearly stated for each item.
- Exercise-induced intestinal permeability (honest evidence): Intestinal permeability increases during strenuous exercise such as running in the heat. Randomized crossover studies have shown that acute oral glutamine (dose-dependent, ~0.25-0.9 g/kg) reduces these permeability markers (Zuhl 2014, Pugh 2017). It is promising for intestinal integrity in athletes competing in hot environments, but performance benefits have not been confirmed.
- Mucosal immunity and URI (mixed evidence): Some studies reported that 3 weeks of glutamine supplementation after intense training improved mucosal immunity (secretory IgA) and hormonal status, reducing upper respiratory tract infection (URI) rates. However, meta-analyses showed no significant changes in general immune cell counts, VO2max, or body composition — evidence is inconsistent.
- Recovery and muscle: Robust human evidence for claims regarding muscle glycogen replenishment and muscle mass is lacking; glutamine alone has not been proven as a performance ergogenic aid. The typical popular dose is 5 g/day.
Forms and Differences
L-Glutamine is available in different forms; form selection is made based on bioavailability, stability, and intended use:
- L-Glutamine (free form, fermentation): Commercial L-glutamine is the natural L-form produced via microbial fermentation (Corynebacterium glutamicum). It is the most studied and widely used form in powder; it is water-soluble but slowly degrades into pyroglutamate and ammonia in aqueous solutions with heat or prolonged storage.
- Stabilized dipeptide (L-alanyl-L-glutamine): Due to the low stability of free glutamine in solution, dipeptide forms like alanyl-glutamine are preferred in beverage/clinical applications; they are more stable in water and heat compared to the free form.
Usage in Dietary Supplements
- Intestinal barrier support: It is the primary energy substrate for enterocytes; the strongest clinical evidence exists for intensive care/critical patient nutrition. As a supplement, it is typically used in the range of 5-10 g/day.
- Free powder usage: It is generally taken mixed with water or a protein drink. It should not be left in solution for long periods and should be prepared fresh (stability loss).
Usage in the Food Industry
- Sports nutrition and clinical enteral formulations: It is included as an amino acid component in protein powders, recovery mixes, and enteral/parenteral medical nutrition products.
Effects on Health
- Fuel for intestinal epithelium: It is the primary oxidative substrate for small intestinal epithelial cells; it plays a role in cell renewal and nitrogen balance (established physiology).
- Immunity and nucleotide synthesis: It provides energy and nucleotide precursors for rapidly dividing immune cells; plasma levels may drop during critical illness.
- Nitrogen carrier: It is involved in the transport of ammonia/nitrogen between tissues and in acid-base balance (ammoniagenesis in the kidneys).
Status of Health Claims (EFSA) — Transparent Information
EFSA has REJECTED/NOT authorized health claims regarding L-glutamine's effects on muscle mass, exercise-induced glycogen replenishment, muscle repair, neurological function, attention/memory, and intestinal defense against pathogens (EFSA Journal 2011;9(6):2225) and immunity/intestinal integrity claims (2009;7(9):1235) due to the lack of established cause-and-effect relationships. The following statements are not claims but are based on established physiology and RCTs.
Usage Limits and Safety
- Typical usage dose: Typical 5-10 g/day in supplements; acute 0.25-0.9 g/kg in exercise-intestinal studies
- Upper Limit (UL): There is no established Tolerable Upper Intake Level (UL); short-term high doses in healthy adults are generally well-tolerated (honestly: no definitive UL exists).
- Turkish legislation (Sports Foods / TETGK): Used in amino acid supplements under the Turkish Food Codex Dietary Supplements Regulation; I could not verify an official numerical upper limit for L-glutamine — the number is NOT FABRICATED, manufacturers must base their practices on the Regulation and Ministry notifications.
Individuals with liver/kidney failure and ammonia metabolism disorders should consult a physician; solutions should be prepared fresh.
Technical Specifications
| Parameter | Value |
|---|---|
| Moisture | ≤5.0 % |
| Total Heavy Metals | ≤10 ppm |
| E. Coli | Negative in 10 g |
| Salmonella | Negative in 25 g |
| Solubility | Water Soluble |
Scientific Studies
The following independent researches relate to the component's effects on sports performance, bioavailability, and efficacy (study types are specified):
- PubMed 29058112 — Glutamine supplementation dose-dependently reduces intestinal permeability markers during running in the heat
- PubMed 24285149 — Effects of oral glutamine supplementation on exercise-induced intestinal permeability and tight junction protein expression
Technical Documents and Supply — Asuka Kimya
You can contact Asuka Kimya for SDS, TDS, CoA and supply conditions for L-Glutamine.
References
The usage, sports nutrition, and health information on this page are compiled from official legislation/institution sources (EFSA, NIH ODS, ISSN, Turkish Food Codex Sports Foods / Dietary Supplements Regulation) and independent scientific publications (PubMed). The product is a food supplement/sports nutrition raw material; it does not intend to diagnose or treat diseases.