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Things you didn’t know branched-chain amino acids do for your immune system

Branched-chain amino acids (BCAAs) are well known for their abilities to prevent muscle degradation and promote protein synthesis.

With this article, I’d like to talk about some fewer known benefits of BCAA supplementation. That is, their effects on the immune system.

For a more complete guide to BCAAs (i.e. uses, doses, timing, etc.) check out an earlier article I wrote here.

What are BCAAs?

Amino acids are biological units that make up proteins. Together with proteins, the two are often referred to as the building blocks of life.

Branched-chain amino acids (BCAAs) are a group of amino acids – leucine, isoleucine, and valine – essential to the diet.

They are essential because our body lacks the ability to produce them itself. Therefore, the only way to get them is by ingesting them in food or from a supplement.

While most amino acids that arrive in our system from the diet are broken down in the liver, BCAAs can be fully metabolized within the mitochondria of skeletal muscle. The products of their breakdown can be used to generate energy and it was long ago observed that exercise increases BCAA metabolism.

Because of these findings, many people started looking at the use of BCAAs to increase athletic performance.

A lot of the research looking at BCAAs directly influencing athletic performance have not shown anything conclusive.

The best people have found is an increased time to exhaustion during aerobic exercise, decreased mental fatigue, increased processing accuracy, decreased perceived exertion, and decreased reaction time.

There is better scientific evidence regarding BCAAs as being able to prevent protein degradation during exercise and stimulate protein synthesis.

But, these topics have been covered extensively in other articles (“5 Proven Benefits of BCAAs (Branched-Chain Amino Acids”, “BCAAs: The Many Benefits Of Branched-Chain Amino Acid Supplements”).

I’m going to spend some time talking about some aspects of BCAAs that don’t get as much attention: their ability to influence the immune system.

Exercise and the immune system

Exercise, from the point of view of your body, is a form of trauma. In fact, mild trauma to the muscle is absolutely necessary for adaptation (i.e. getting stronger) to occur.

If, however, you go too hard too fast, don’t allow sufficient time to recover between workout sessions, or participate in a really strenuous athletic event – like a marathon or a tournament of some kind – you can develop a chronic form of tissue trauma.

As a general rule of thumb: anything chronic usually isn’t good. In this case, chronic mild tissue trauma isn’t good for your muscles and it’s not good for you on the whole.

To prevent trauma from crossing into the chronic “no fun zone”, your body mounts an immune response.

An immune response is the same thing that happens when your body tries to defend itself against bacteria, viruses, and anything else that your body comes into contact with and recognizes as harmful.

In little doses, the immune response is a good thing. It helps stimulate the repair required to get stronger.

If you push your body too far and constantly stimulate the immune response without giving it a chance to shut off, you can develop a persistent immune response that throws off the balance of immune cells within the body.

Besides delaying strength building and adaptation to exercise, this can have negative effects elsewhere in the body too: you get sick easier because your ability to defend against microorganisms invading the body goes down.

BCAAs regulate the immune response by maintaining glutamine levels in the blood

Glutamine is another amino acid. In humans it is the most abundant amino acid found circulating in the blood.

Certain types of immune cells, like lymphocytes for example, use glutamine to function properly.

Prolonged periods of intense exercise – the kind that puts you into the category of chronic trauma and a chronic immune response – may cause working muscles to dump less glutamine into blood circulation.

Less glutamine in the blood means there is less available for cells like lymphocytes and they may then not be able to function properly when a little invader enters your body. The result: you get sick easier.

BCAA supplementation has been shown to prevent the decrease in glutamine circulating in the blood associated with intense exercise bouts.

BCAAs maintaining blood glutamine levels means they support your immune system and keep your defenses up so you don’t kick sick as a result of over-exercising.

BCAAs regulate the immune response by keeping things balanced

Overly strenuous exercise can cause certain cells in the body to release a specific combination of signaling molecules called cytokines.

These cytokines cause immune cells in the blood to skew towards humoral immunity and suppress cell-mediated immunity.

Humoral immunity is a type of immune response where immune cells secrete molecules into the space around them. These molecules tag invaders for death or damage the invaders so badly that they die.

Cell-mediated immunity is a type of immune response where immune cells deal with invaders directly.

Knowing the differences between humoral and cell-mediated immunity isn’t as important as knowing that cell-mediated immunity is suppressed as a result of over-strenuous exercise.

This can leave you more susceptible to infections, which is why some researchers think athletes are more susceptible to upper respiratory tract infections than the general population.

BCAA supplementation is associated with regulating the signaling molecules (cytokines) that throw the balance of humoral and cell-mediated immunity out of whack.

Regulated cell-mediated immunity means you’re less susceptible to unwanted infections as a result of strenuous exercise.


BCAAs have been researched and used in sport and workout supplementation for over 40 years. In that time, we’ve learned lots about their ability to promote muscle building and prevent muscle degradation as a result of exercise.

But, BCAA supplementation has important effects on the immune system that will help keep your body able to defend itself against things that could potentially make you sick.

Be sure to check out my other article on BCAAs to learn more about dosing and more information about the other uses of BCAAs. If you have any more questions, post them in the comments below, I’d love to help you out!

Sources and further reading

Branched-chain amino acid supplementation does not enhance athletic performance but affects muscle recovery and the immune system


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