A deeper look into L-glutamine and athletic performance - by Michelle Reed

L-glutamine (Glu) is a well-known amino acid in the sports nutrition world for its various physiological functions, but do athletes actually know why they supplement with it?

In this article, I will shed some light on the benefits of supplementing with Glu.

Let’s start with the basics: amino acids are constituents of proteins, which are highly important for all physiological processes in the body to occur. Glu is a non-essential amino acid (the body is able to make it itself), it is the most abundant of amino acids in the body, and approximately 60 per cent of skeletal muscle is made up of Glu.

Glu is constantly utilised by the body and is in particularly high demand during times of stress or when completing a high-intensity training session or big training block. Although the body can make it, our supply is often limited.

Glu is found in foods such as animal and plant proteins (highest in casein and whey protein) or as a powdered or capsuled supplement. It is important to be aware that many people (especially athletes) do not get enough Glu from food alone.

The most common uses that science has shown for Glu in the sporting world are weight loss and building muscle mass. While this remains the case, science is now providing insights into how Glu improves athletic performance on a deeper level through immunity, digestive health and recovery.

Other functions of Glu include it being a desired nutrient during gluconeogenesis. This is the formation of carbohydrates within the body during the transformation of glucose to lactate when limited amounts of oxygen are available. It is therefore a valuable resource for short and intense exercise.

Glu is also essential for acid-base balancing, it serves as a nitrogen donor in the formation of nucleic acids and the maintenance of nitrogen transfer between organs, and it is required for the detoxification of ammonia (a toxic waste product created when the body breaks down protein).

Let’s take a deeper look into how Glu may support an athlete: 

Body composition

A double-blind study (1) tested 30 male subjects for performance and blood hormone concentrations before and after an 8-week period, with 15 subjects supplementing with Glu and the other 15 with a placebo.

The study showed that both groups increased their performance; however, the Glu group showed significantly greater increases in upper and lower body strength, explosive muscular power and blood testosterone.

The Glu group also had significantly lower cortisol concentrations compared to the placebo group. This is important for increasing performance and body composition because a prolonged increase in cortisol can cause hormonal imbalances and disrupt inflammation regulation. 

Immune support

As an athlete, immune support is fundamental. During training, inflammation is naturally increased and immune system cells have higher glutamine requirements, meaning that the bloodstream and tissue concentrations of Glu can fall. These lower Glu concentrations limit the ability of immunological tissues to achieve optimal function. 

Research has shown that there is a decrease in plasma Glu concentrations during prolonged exercise and high-intensity training (2). This reduction commonly results in exercise-induced immune impairment and, therefore, the inability to fight infections.

The immune strength of an athlete is a key factor for ensuring the athlete can get the most out of their training, train consistently and be fit and strong when it matters the most.

Glu strengthens immunity by acting as a precursor of the antioxidant glutathione, along with amino acids cysteine and glycine. Glutathione is a master detoxifier and maestro of the immune system.

This information provides a key motivation for Glu supplementation; reducing the likelihood of an athlete becoming ill during large blocks of important training and supporting their immunity during the competitive season. 

Digestive health

Long-term Glu supplementation has also been shown to reduce exercise-induced intestinal permeability. Research shows this is due to its ability to inhibit the NF-κB pro-inflammatory pathway in human peripheral blood mononuclear cells (3). Since inflammation is an important process in creating adaptation during and after exercise, the NF-κB pathway is naturally increased.

However, when inflammation is constantly being created due to daily and multiple training sessions, poor dietary habits (high consumption of dairy, meat, coffee, processed foods and sugar), lack of sleep, stress and heat shock activation, it is difficult for the body to regulate the inflammation efficiently. This rise in inflammation can slow down recovery time and cause undesired health issues.

A common effect of increased inflammation is impaired digestion or intestinal permeability (leaky gut). Tight junctions, which are found along the mucosal lining of the gut, regulate what is absorbed. When these tight junctions are damaged, causing an inflamed and irritated gut lining, our ability to absorb vital nutrients from food is heavily reduced.

This can place a huge burden on an athlete’s performance through loss of energy, mood and hormonal imbalances, illness, allergies or weight gain.

Research suggests that an acute dose (5g) of oral Glu prior to exercise reduces intestinal permeability and decreases heat shock activation (produced due to a rise in temperature), leading to inhibited pro-inflammatory markers and gut lining repairs. Glu is also the preferred source of fuel for enterocytes (cells of the intestinal lining), making it an essential nutrient for digestive health. 


Supplementing with Glu may help speed up recovery by aiding the protein synthesis important for muscle regeneration, balancing pH (acid/base) levels and reducing the delayed onset of muscle soreness.

Glu also helps to regulate inflammation, an important aspect of speeding up recovery. A study (3) showed that the inflammatory marker TNF-α was lower four hours post-exercise in the Glu group compared to a placebo group, showing its potential to lower post-exercise inflammation. 

Dosage, usage & warning

The most researched dosage of Glu is 5g/day and for athletes to consume it twice per day.

Directions for use:

  • - First thing in the morning on an empty stomach
  • - After high-intensity training or prolonged exercise periods
  • - Ensure usage throughout heavy training periods

Warning: The up-regulation of glutamine supplementation may be excitatory in some individuals.


  1. Hakimi M et al (2012). The effects of glutamine supplementation on performance and hormonal responses in non-athlete male students during eight week resistance training. J Hum Sport Exerc. 7(4):770–82.
  2. Rao R & Samak G (2012). Role of Glutamine in Protection of Intestinal Epithelial Tight Junctions. J Epithel Biol Pharmacol. 5(Suppl 1-M7):47–54.
  3. Zuhl M et al (2015). The effects of acute oral glutamine supplementation on exercise-induced gastrointestinal permeability and heat shock protein expression in peripheral blood mononuclear cells. Cell Stress Chaperones. 20(1):85–93.

To view more from Michelle, visit her Facebook page and Instagram.