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

If it is good enough for Mr Olympia, then it may be good enough for you.

Phil Heath is the reigning, now 5 time Mr Olympia; making him the current best professional bodybuilder in the world. The dietary supplements used by the man with the worlds best body should therefore be considered by all folks interested in optimising their nutrition and training.

In a breakdown with the Bodybuilding magazine Flex[1], “The Gift” describes that alongside the standard whey protein and branched chain amino acids, during his pre-contest prep he will consume another supplement up to three times per day: L-Glutamine.

And Phil is not on his own, MyProtein ambassadors Owen and Lewis Harrison also list l-glutamine as one of their favourite supplements.

But what is glutamine? What does it do and how can it help you to improve your performance and physique? Read on to learn more…

What Is Glutamine?


Glutamine (often called l-glutamine or 2,5-diamino-5-oxo-pentanoic acid) is the most abundant amino acid found in our blood[2] and makes up approximately 60% of the amino acid pool in our muscles[8]. It is constructed by combining an amine acid compound and glutamic acid.

It is considered conditionally essential, meaning that in certain situations its synthesis can be limited (e.g. in premature infants or those in intensive care). In this circumstance it means that it would need to be consumed in the diet via food or supplementation.

It is synthesized predominantly in skeletal muscle (approximately 90%) by a process facilitated by the enzyme glutamine synthetase from the amino acid glutamate and glutamic acid[3].

In healthy individuals it can be produced with no problem in the muscle, which is able to produce, store and release glutamine as required to maintain the appropriate glutamine blood concentration[4].

However, during some situations the production of glutamine homeostasis is threatened, glutamine reserves in skeletal muscle are depleted, and the important functions of this amino acid are inhibited. Such situations would include various forms of catabolic stress ranging from infection, surgery and, importantly, exhaustive exercise!

What Does Glutamine Do? Muscle Growth!


gym wear

Glutamine is an amino acid known for its role as a substrate for protein synthesis[5]. This means it is used during skeletal muscle contraction when we exercise, and without its presence our gut wrenching exercise sessions may be hampered.

This amino acid is an important anabolic precursor for muscle growth following exercise[6]. In fact it the anabolic effects of glutamine include both an increase in protein synthesis (muscle hypertrophy or increased number of muscle cells)[9] and increases in muscle cell expansion and filling with creatine, water and carbohydrate (muscle cell volumisation or “the pump”)[10].

The specific mechanisms of these benefits have not been fully explained, however certain physiological actions have been attributed to glutamine concentration in muscle.


Important Amino Acid: Leucine


Firstly, increased glutamine content in muscle allows glutamine to suppress the oxidation (breakdown) of the branched chain amino acid leucine, and enhances the disposal of leucine without release of free radicals[9]. Remember, free radicals are atoms with an unpaired electron which reL Glutamine | What Is It and What Does It Do? Benefits? Side Effects?act with oxygen to reek havoc and result in cell damage.

The presence of leucine is key for muscle growth as it regulates the initiation of protein synthesis, acting as a trigger for muscle tissue de
velopment[11]. Therefore, if glutamine can prevent leucine breakdown, it can be put to better use to facilitate muscle synthesis.

The concentration of glutamine also ensures a positive nitrogen balance which is required for muscle protein synthesis[12]. There is also evidence that glutamine can also reduce muscle tissue catabolism (breakdown) by counteracting the effects of the stress chemical cortisol. Cortisol is an adrenal stress hormone which can lead to proteolysis (protein tissue breakdown) and reduced physical performance[13].

What Does Glutamine Do? Immune Boost!


The various other physiological roles of glutamine include facilitation of nitrogen metabolism; balance of acid-base levels in the kidney; and its position as an important fuel source for the immune system[7].

In situations of reduced glutamine production (as seen in critical illness) a subsequent reduction in the glutamine concentration of muscle and plasma occurs[7]. Research has demonstrated that supplementation of glutamine in such circumstances can lead to improvements in immune system function[14].

This is due to the fact that immune system cells (e.g. lymphocytes and macrophages) are fuelled either in equal measure, or more so, by glutamine (rather than glucose)[15-16]. Therefore, if glutamine levels are reduced, immune system cells will have a reduction in fuel source to work efficiently.

How Does Exercise Effect Glutamine Levels?


gym training

Training intensely (as we all try to do) or performing exhausting exercise such as marathon running, has a profound effect on the glutamine levels in your body. In fact levels may decrease even as much as 20-30%[4].

It has been shown that a significant reduction (24%) in plasma glutamine concentration was caused by day 3 following an intense eccentric strengthening session for the biceps, triceps, hamstrings and quadriceps[18] which lasted until at least day 9 following the session.

Another study demonstrated that two hours following 40 repetitions of a leg press at 80% 1 rep max, glutamine levels in the quadriceps had been reduced by 34% in the type I muscle fibres, and 29% in the type II fibres[19].

Natural glutamine reduced = limited muscle growth!

As such if glutamine homeostasis is altered, it is likely that the aim for muscle growth during these exercises will be limited! The resulting effect on performance will be reduced strength, reduced power, reduced endurance and longer time to recovery.

It is postulated that the reduction in glutamine levels is a result of increased glutamine removal by the liver and increased use of glutamine by the kidneys and the immune system. It is also thought that such reductions of glutamine may contribute to a susceptibility to infection[20]. The effect of over-training has also shown that this susceptibility may continue after several weeks of rest[21].

What Are The Benefits Of Glutamine To Me?


We have established the role of glutamine in our muscles, and discussed the risk of glutamine depletion following intense exercise.

Now we need to ask- can this be rectified with increasing glutamine intake and if so what are the specific benefits I can expect?

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

Below I outline these potential benefits.

✓ More gains!
In combination with protein (casein or whey) glutamine assists an increase of muscle protein synthesis by 8.3% (compared to protein alone, or protein with other essential amino acids)[22].

✓ Quicker Recovery!
Reduces time to full muscle recovery of strength following exercise [23-24] and protects against the negative effects of oxidative stress chemicals following intense exercise, therefore improving the beneficial effects of high intensity training on muscle protein synthesis[25].

✓ Less Muscle Wastage!
When part of an amino acid stack glutamine contributes to the suppression of the loss of muscle following periods of extended rest (e.g. post injury or surgery)[26].

✓ Feel less tired!
Glutamine reduces the perception of fatigue in football players (in combination with l-carnitine and carbohydrate)[27].

✓ More lean muscle!
In combination with intense training glutamine can assist increases in body mass and, more importantly to us all, lean body mass[28].
✓ Improved Power!
Improvements in initial rate of power production as demonstrated by an improved vertical jump performance compared to a placebo supplement[28].

✓ Better Endurance!
Increases running performance by increasing the time until muscular exhaustion[29].

✓ Less DOMS!
Diminishes post work out soreness[23-24].

✓ Better Immunity!
Reduces the incidence of infection in trauma and surgical patients and reduces the length of time spent in hospital[30-32].Also, improves intestinal function and reduces susceptibility to infection in athletes during the post training period[17]; and assists restoration of key immune system markers (e.g. T cell counts, immunoglobulin A serum) following heavy load resistance training reducing risk of infection post training[33].

✓ Quicker reactions!
Improves reaction time following exhaustive endurance exercise[34].

✓ A Stronger heart!
Enhances cardiac hormone levels to assist better management of heart function and blood pressure[35].

✓ Improved Power!
Improvements in initial rate of power production as demonstrated by an improved vertical jump performance compared to a placebo supplement[28].

Where From & How Much?


As stated previously glutamine is considered “conditionally essential”- meaning at most times the body will produce enough for our muscles to function. However, the “condition” is that we do not place ourselves in a position where we are catabolic.

We have also shown that intense exercise sessions CAN place us in such a position, leading our gains to be inhibited and increasing our potential to get sick! As such we should aim to up our glutamine levels when ever we train intensely.

Obviously there are dietary sources of glutamine, which include beef, chicken, fish, eggs, beans, dairy products, cabbage, spinach and beets. However, many of us may also like to supplement glutamine in powder or tablet forms, as consuming sufficient food stuffs may be impractical immediately following exercise- during the window when our glutamine is depleted the most.

L-Glutamine Dosage

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

In order to sustain a positive net protein balance and ensure the above listed benefits of supplementation, orally ingested glutamine can start with 0.1g/ kg of body mass (e.g. 7g for a 70kg individual) and result in a 50% rise in the plasma glutamine concentration 30 minutes following exercise. Return to pre-exercise baseline concentration should occur 1-2 hours following ingestion[32].

Ingestion alongside a protein source (whey or casein) and a BCAA supplement seems to provide even more superior advantages to glutamine alone[22, 26], which is perhaps another reason to add a glutamine powder directly to your post exercise shake.

Studies have shown that oral ingestion of up to 28g PER DAY for 6 weeks result in no adverse effects[36]. Furthermore, increasing post exercise dose to 0.65g/ kg of body mass (e.g. 45.5g for a 70kg individual) was also tolerated well by healthy individuals[36].

Take Home Message


Glutamine is an important component of our muscles and if we aim to exercise and improve the size, look and function of our muscular system we should be wary of keeping glutamine concentration in check.

If you are exercising with sufficient intensity and often you run the risk of over-training, leading your prone to limiting your gains and increasing your susceptibility to getting sick.

Use a glutamine supplement as part of your post work out stack to minimise the detriment of glutamine loss and keep your progression from plateauing.

If it’s good enough for Phil… who are we to argue!




Writer and expert