Glutamine is one of the body’s most-utilized amino acids. It’s the primary fuel source for several different types of cells including those lining the intestinal tract (enterocytes) and a variety of immune system cells (leukocytes).

Glutamine is the most abundant amino acid found in the blood stream and the muscles, which serve as reservoirs in times of need. ‘Need’ can be defined as instances like prolonged exercise, trauma, infection and starvation, to name a few. In other words, glutamine is a quick energy source for the cells during stress.

Because of its widespread use in the body, glutamine has been very heavily researched. In the area of sports medicine, glutamine has been shown to be an important supplement that endurance athletes should consider as part of their nutrition regimen.

It’s well known that excessive training depletes both the blood and muscle reservoirs of glutamine. Glutamine is a key factor in these areas:

Muscles

Excess or overtraining causes plasma (blood) levels of glutamine to drop, as tissue demand drastically increases from the stress of training.

This is part of why, in an overtrained or overreaching state, recovery is prolonged – the muscles are left with low reserves after attempts at recovery from ‘normal’ bouts of exercise.

Once overtraining starts happening, the muscular system doesn't have the amount of glutamine it needs for repair.

GI System 

Insufficiency of glutamine can lead to serious consequences in the gut as well.

If the enterocytes main energy source is inadequate, the intestinal barrier as a whole may be weakened, allowing for easy passage of inadequately digested food proteins, bacteria and other toxins.

Once this occurs, the immune system (located on just the other side of the intestinal wall), is now primed for an inappropriate allergic response, irritable bowel syndrome or GI illness.

In other words, this sets the stage for leaky gut and all of its sequela.

Immune Function

Additionally, lower plasma stores of glutamine also contribute to immune dysfunction, as decreased availability of the leucocytes’ main fuel source may compromise optimal immune function.

While studies are conflicting as to the direct benefits of glutamine supplementation and illness prevention, we do know that the rates of illness are accurately linked to an athlete’s levels of plasma glutamine.

Endurance training is associated with several biochemical and hormonal changes that are known to alter immune function. 

Because of this relationship, all athletes should be encouraged to eat a diet with balanced (and adequate!) amounts of the macronutrients (carbohydrate, protein and fat), as well as the essential micronutrients (vitamins and minerals), at the very minimum.  

I would also add glutamine supplementation to this list because of its relationship to immune, gut and muscle health.

Ensuring Adequate Glutamine Levels

The richest dietary sources of glutamine include fish, meats, beets, raw cabbage and legumes. Unfortunately, glutamine is easily destroyed by heat, and the aforementioned foods are best consumed after some degree of cooking, which may negate their use a direct supply of glutamine.

Despite this, consuming protein and more specifically proteins that contain branched chain amino acids (leucine, valine and isoleucine) is the most ideal way to augment glutamine stores. Branched chain amino acids are recruited to create glutamine; this is how most of the body’s glutamine needs are met. 

However, it’s important to remember that due to the widespread use and demand for glutamine, it may be advantageous to supplement with it to prevent the previously mentioned issues in the muscles, gut and immune system.

Remember, exercise isn’t the only factor that can contribute to low glutamine levels – infections, injuries, and suboptimal nutrition (inadequate protein intake) can also consume your glutamine stores!

I recommend supplementing with glutamine if any of the above situations pertain to you. A dose of 1500 mg twice daily should do the trick, as long as you’re eating a balanced diet; other situations may be cause for greater amounts.