Glutamine

What is glutamine and what does it do in the body?

According to NIH ODS, glutamine is the most abundant amino acid in muscle, blood, and the body’s free amino acid pool. It is synthesized in the body mainly from branched-chain amino acids (BCAAs); an adult takes in about 3–6 g of glutamine per day from protein-rich foods. Glutamine is an important molecule in metabolism and energy production and supplies nitrogen for many critical biochemical reactions. When the body’s glutamine need in severely ill patients exceeds its production capacity, glutamine behaves like an essential amino acid. ^[1]

In the Cochrane review, glutamine is described as a conditionally essential amino acid whose own production may not meet tissue needs in states of metabolic stress. ^[7] This conditional state is not the same as a healthy athlete benefiting from extra glutamine; the sections below address the two contexts separately.

In what forms and for what purpose is glutamine supplemented?

In sports studies, glutamine has been examined in the forms of free L-glutamine and glutamine dipeptide. ^[4] Some athletes use glutamine supplements in the hope of reducing exercise-induced immune suppression and lowering the risk of upper respiratory tract infection; ODS states that there is no research-based support for this benefit. ^[1] According to Gleeson, some athletes may already take high amounts of L-glutamine because of high energy and protein intakes, protein supplements, protein hydrolysates, and free amino acids. ^[5]

Does glutamine work for muscle gain and performance?

According to ODS, few studies have examined the effect of glutamine alone as an ergogenic aid. In the 2001 study by Candow and colleagues, 31 people aged 18–24 (17 in the glutamine group, 14 in the placebo group) did whole-body resistance training for 6 weeks and received glutamine or placebo (maltodextrin) in a double-blind fashion. With training, 1-repetition maximum squat and bench press strength, knee extension torque, lean tissue mass, and urinary 3-methylhistidine (a marker of muscle breakdown) increased; no significant difference was found between groups. The authors concluded that glutamine had no significant effect on muscle performance, body composition, or muscle protein breakdown in young healthy adults. ^[2]

A 25-study meta-analysis of glutamine supplementation in athletes (from a 47-study systematic review) concluded overall that glutamine had no effect on athletes’ immune system, aerobic performance, or body composition. The same analysis reported a mean reduction in body weight of −1.36 kg (95% CI −2.55 to −0.16) in glutamine users, a decrease in neutrophil count at doses above 200 mg/kg (WMD −605.77; 95% CI −1,200.0 to 52.1; P=0.03 is given in the abstract, but the interval includes zero), and higher post-exercise blood sugar with glutamine dipeptide (WMD 0.51 mmol/L; 95% CI 0.18–0.83); no association was found with other outcomes. ^[4] This row is therefore graded E.

Does glutamine speed recovery after exercise?

The 2015 study by Legault and colleagues is a double-blind, placebo-controlled, crossover study in 16 healthy participants (8 women, 8 men; age 22 ± 4). Participants took glutamine or placebo once daily for 72 hours and performed a single-leg eccentric knee extension exercise. Glutamine was associated with higher relative peak torque at 180°/s immediately after exercise (71 ± 8% vs 66 ± 9%) and at 72 hours (91 ± 8% vs 86 ± 7%), and with lower muscle soreness scores at 24, 48, and 72 hours. In men, torque was also higher at 30°/s; the authors state that the effect may be more pronounced in men than in women. ^[3] NIH ODS summarizes the same study as glutamine reducing strength loss, speeding strength recovery, and reducing soreness more quickly; the effects are more pronounced in men. ^[1]

This is a single, small study. Gleeson’s 2008 review states that the reasons proposed for glutamine supplementation (immune support, increased glycogen synthesis, prevention of muscle breakdown) receive very little support from well-controlled studies in healthy, well-nourished people. ^[5]

Does glutamine strengthen immunity?

Prolonged exercise and periods of intense training are associated with a drop in plasma glutamine concentration, and it has been suggested that this could be one cause of exercise-induced immune impairment and susceptibility to infection in athletes. According to Gleeson’s review, recent glutamine feeding studies show that, although plasma glutamine concentration can be held constant during and after prolonged intense exercise, supplementation did not prevent changes in various aspects of post-exercise immune function; moreover, although glutamine is required for lymphocyte proliferation, plasma glutamine does not fall after exercise enough to impair the rate of proliferation. ^[5] ODS also states that there is no research-based support for glutamine supplements reducing exercise-induced immune impairment and lowering the risk of upper respiratory tract infection. ^[1]

What has been shown for glutamine in severe illness?

According to ODS, many patients with serious catabolic illnesses such as infections, bowel diseases, and burns use glutamine safely as part of their medical care. ^[1] However, this context differs from the healthy athlete, and the results are not unidirectional.

Adults with multiple organ failure. The REDOXS trial randomized 1,223 adults with multiple organ failure on mechanical ventilation in 40 intensive care units in Canada, the US, and Europe in a 2×2 factorial blinded design to receive glutamine, antioxidants, both, or placebo; supplements were started within the first 24 hours of intensive care admission and given intravenously and enterally. Mortality at 28 days was 32.4% vs 27.2% in those receiving glutamine vs those not (adjusted OR 1.28; 95% CI 1.00–1.64; P=0.05; because the significance threshold was set at P<0.044 owing to the interim analysis plan, this result was reported as a “trend”); in-hospital and 6-month mortality were significantly higher in those receiving glutamine. Glutamine had no effect on organ failure or infection rates; antioxidants also did not affect 28-day mortality. The authors report that early glutamine or antioxidant administration did not improve clinical outcomes and that glutamine was associated with increased mortality in critically ill patients with multiple organ failure. ^[6] (A correction notice [erratum] was later published for the article.) ^[6]

Premature infants. The 2016 Cochrane review evaluated 12 RCTs (2,877 premature infants; 6 enteral, 6 parenteral glutamine). The meta-analysis found no effect on death (typical RR 0.97; 95% CI 0.80–1.17) or on major neonatal diseases such as invasive infection and necrotizing enterocolitis; three studies assessing neurodevelopment at 18–24 months also showed no effect. ^[7]

Sickle cell disease. In the phase 3 study by Niihara and colleagues, 230 patients (ages 5–58) with sickle cell anemia or sickle β0-thalassemia who had had at least two pain crises in the previous year were randomized 2:1 to receive pharmaceutical-grade L-glutamine or placebo; treatment lasted 48 weeks. The number of pain crises was significantly lower in the glutamine group than with placebo (median 3.0 vs 4.0; P=0.005), as were hospitalizations (median 2.0 vs 3.0; P=0.005); two-thirds of patients in both groups were taking hydroxyurea. Mild nausea, noncardiac chest pain, fatigue, and musculoskeletal pain were more common in the glutamine group. The study was funded by the company that developed the product; PubMed lists the same company as the affiliation of some of the authors. ^[8] This finding rests on a single RCT, is disease-specific, and was obtained with a pharmaceutical-grade product; it is not valid evidence for supplements in healthy people.

Are glutamine supplements safe?

According to ODS, no side effects were reported in the athlete studies in which glutamine was examined; no biochemical or clinical evidence of toxicity was found at doses of 0.21–0.42 g/kg body weight per day (15–30 g/day in a person weighing 154 lb ≈ 70 kg), and no safety problem was reported in a 6-week study with about 45 g/day. ^[1] According to Gleeson’s review, acute intakes of about 20–30 g appear harmless in healthy adults, no harm was reported in a study in which athletes consumed 28 g of glutamine per day for 14 days; doses up to 0.65 g/kg of body weight were tolerated in patients and did not produce abnormal plasma ammonia. ^[5]

In the risk assessment by Shao and Hathcock, a classical tolerable upper intake level (UL) could not be calculated for glutamine because there was no systematic pattern of side effects; instead, the “observed safe level” (OSL) method was used: according to published human studies, the evidence for the absence of side effects at supplemental intakes of glutamine up to 14 g per day in healthy adults was found to be strong. Intakes above this level were also tested without side effects and may be safe, but were not selected as the OSL because data on long-term safety were found to be insufficient. ^[9] The affiliation reported in PubMed for one of the article’s authors is a supplement industry association. The OSL is not an upper limit (UL); nor is it an institutional dose recommendation. ^[9]

How are glutamine supplements regulated in Türkiye?

For every dietary supplement to be placed on the market in Türkiye, approval from the Ministry of Agriculture and Forestry is mandatory; applications for approval of imported products can be made only to the Istanbul and Ankara Provincial Directorates. ^[11]

In the latest update of the Ministry’s Dietary Supplements Restricted Substances List (September 21, 2026), the source in the “L-Glutamine” row is “chemical synthesis”; in the daily intake column for ages 11 and over, a value of at most 10 g/day is written, there is no value in the ages 4–10 columns, and the publication date is May 2, 2016. ^[10] This list value (10 g/day) and Shao and Hathcock’s OSL value (14 g/day) belong to different institutions and different concepts.

Evidence table: claim, population, and limits

This guide does not recommend personal doses. In the contexts of severe illness and special clinical nutrition, use is evaluated under physician management.