L-Glutamine: Benefits, Side Effects, Best Time to Take It & More

L-Glutamine

(Glutamine)

Evidence: High
Possible Benefits: Low
Safety: Reasonable

What is L-glutamine?

L-glutamine is a conditionally essential amino acid. It becomes essential during periods of physical trauma or certain diseases. As a supplement, it is often used for improving exercise performance. While glutamine is not very effective in this regard, supplementation can be beneficial in other areas. This article is about the main benefits of L-glutamine, its potential side effects, the best time to take it, and more.

What does L-glutamine do for the body?

Glutamine is a conditionally essential amino acid. It becomes essential during periods of certain diseases or muscle wasting. Even when you do not need to consume it to survive, this amino acid still plays an important role in human health.

L-glutamine is a building block for proteins, amino acids, and glucose. It mainly plays a role in immune and intestinal health.

While this amino acid is believed to be great for building muscle mass, this is mostly a myth. When ingested by a healthy adult, glutamine gets taken up by the small intestine, and very little reaches the muscles.

Doses beyond 0.75 g/kg of body weight have been shown to increase serum ammonia.

Possible benefits

All of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.

Major benefits

Healing physical trauma – While glutamine is ineffective for building muscle mass in healthy individuals, it can help those suffering from physical trauma such as burns or muscular wounds to regain muscle mass. This also applies to people with diseases in which muscle wasting occurs, such as AIDS.
Reduced symptoms of sickle cell disease – The supplement can reduce sudden complications of sickle cell disease.

Minor benefits

Improved intestinal health – The vast majority of glutamine in the body is utilized in the intestines. Supplementation can improve intestinal health in those who do not consume or synthesize enough glutamine.
Reduced symptoms of Crohn’s disease – Unfortunately, this benefit is minor and unreliable.
Increased exercise capacity with heart conditions – One study has noted acute benefits in chronic stable angina with 80mg/kg oral glutamine supplementation.

Possible side effects

These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.

Increased blood glucose – Glutamine can be directly converted into glucose after ingestion, which results in an increase in blood glucose.
Toxicity – While acute toxicity has never been reported, taking high amounts of L-glutamine could lead to chronic toxicity and cause some health problems. For example, doses beyond 0.75 g/kg of body weight have been shown to increase serum ammonia. To prevent chronic toxicity, it is best to stay below 20 grams a day unless you have a great reason to take more.
Amino acid imbalance – Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.

Who should not take L-glutamine?

You should probably avoid taking the supplement if you:

get enough L-glutamine from food
experience a severe adverse reaction after taking the amino acid
suffer from a disease in which muscle wasting occurs, such as AIDS

Who will benefit the most?

You should consider taking the supplement if you:

suffer from sickle cell disease
suffer from physical trauma (such as burns or muscular wounds)
suffer from a disease in which muscle wasting occurs, such as AIDS
are on a vegan or a vegetarian diet
don’t eat dairy
consume very little protein (less than 0.3 grams/pound of body weight)
do lots of prolonged endurance exercise

How much L-glutamine should you take?

Since this amino acid can be found in food or synthesized in the body, you may already get sufficient amounts without taking it as a supplement. About 0.36 grams of protein/pound of body weight should generally be enough to prevent any symptom deficiency.

If you plan to take L-glutamine as a supplement, 5-10 grams appears to be the best daily target for most people. This amount should provide most of the benefits without meaningful side effects.

Some people may benefit from doses higher than 10 grams. These include people with intestinal issues and those with severe physical trauma (such as burns or muscle wounds from stabs).

The upper safety limit for glutamine is not well-established. The “observed safety limit” for glutamine has been set at 14 grams per day.

To stay on the safe side, don’t take more than 20 grams daily unless you have a great reason to do so. Higher amounts may cause problems if you take the supplement for a prolonged period.

Food sources of L-glutamine

Glutamine is found in all whole foods that contain dietary protein.

The amount of L-glutamine per gram of protein varies from food to food but a general rule of thumb is that the more protein you eat, the more glutamine you are getting from food.

Best time to take L-glutamine

Like most other amino acids, L-glutamine is water-soluble, so you don’t have to take it with food to absorb it well. Taking the supplement with food is better if it causes stomach upset when you take it on an empty stomach.

Whether you take the supplement in the morning or the evening doesn’t matter much. It should not interrupt your sleep in any way.

If you practice time-restricted eating, take this amino acid during your eating window to guarantee it won’t break your fast.

Unless it feels too impractical, spread the daily dose into 2+ smaller doses throughout the day.

Interactions

Other amino acids
Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.

Glutamic acid vs glutamine

L-glutamine and glutamic acid are related to each other but they are not the same.

Glutamine can be derived from glutamic acid. However, most glutamic acid turns into glutamate in the body.

Glutamine and glutamate have distinctly different biological functions, purposes, and benefits. They are both necessary for optimal human health, but the terms should not be used interchangeably.

While glutamine is a popular supplement, neither glutamate nor glutamic acid is taken very often.

Where to buy L-glutamine

Amazon is the best option for ordering glutamine supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.

Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.

FAQ

You can take the amino acid daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it daily. Not taking the supplement every once in a while could lead to better absorption. That is yet to be proven or disproven.

All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatin, which rarely comes from an ethical source.

Yes. Most amino acids, including glutamine, absorb and digest well if you take them before falling asleep. The supplement should not impact sleep quality in any significant way.

This amino acid should not become harmful once it exceeds the expiration date but can lose potency over time.

Keep the supplement in a cold, dark, and dry place, and it should remain just as potent for many months or even years.

While toxicity is rare, too much glutamine in the system can cause some health problems, often related to increasing serum ammonia. It is best to stay below 20 grams a day to prevent these side effects.

You may need more of this amino acid if you:
– suffer from physical trauma (such as burns or muscular wounds)
– suffer from a disease in which muscle wasting occurs, such as AIDS
– do lots of prolonged endurance exercise
– eat very little protein (less than 0.3 grams/pound of body weight)
– are on a vegan or a vegetarian diet
– don’t eat dairy

The half-life of glutamine in the body is about 1.8 hours. This amino acid stays in your system for about 10 hours after you consume it.

In the long term, you need to take the supplement for about 2-4 weeks to begin noticing the benefits.

You can easily find vegan-friendly L-glutamine pills and powders but always check the label to be sure. If you buy the amino acid in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.

Like most other amino acids, L-glutamine is water-soluble, so you don’t have to take it with food to absorb it well.

L-glutamine should not break a fast unless you take a very high dose at once. If you practice time-restricted eating, take this amino acid during your eating window so it doesn’t break your fast.

References

Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.

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