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Branched-Chain Amino Acids: BCAAs (An Overview)

Updated: Aug 15

Evidence-Based. Scientifically Reviewed by Michael Sharpe, MSc.

Branched-chain amino acids (BCAAs) are an interesting supplement, some studies suggest an improvement in muscle growth, while other studies suggest a decrease.

In this article, I'll explain everything you need to know about BCAAs, their roles, how they work, their benefits, and more.

Table of Contents:

supplement bottle with BCAAs pouring out

What Are They?

BCAAs (Branched-Chain Amino Acids) are a group of three important amino acids that can promote muscular development.

Supplementation isn't required for most individuals since they're already found in high concentrations in foods like meat.

Leucine, isoleucine, and valine are the three amino acids that make up branched-chain amino acids. They are part of the 9 essential amino acids.

They may enhance muscle protein synthesis and boost muscular development in individuals who have a low dietary protein consumption.

Supplementation may also be utilised to keep inexperienced athletes from becoming fatigued.

Isoleucine stimulates glucose absorption into cells, while leucine plays an essential function in muscle protein synthesis. Valine's function in a BCAA supplement needs to be investigated further.

BCAA supplementation reduces the loss of amino acids in the bloodstream that happens during exercise. A drop in levels would usually result in an influx of tryptophan into the brain, followed by the synthesis of serotonin, which induces tiredness.

These amino acids are essential to consume on a regular basis, although many protein sources already include BCAAs, such as meat and eggs.

Supplementation is unnecessary for individuals who consume an adequate amount of protein (~50-100 grams per day).

Their Roles

The three BCAAs have specific roles and functions within the body. BCAAs help to increase protein synthesis and turnover, as well as signalling pathways and glucose metabolism. (4, 5)

BCAA oxidation may enhance fatty acid oxidation and contribute to obesity. (4)

They also have a role in the immune system and brain function in the body.

BCAAs are needed for lymphocyte development, proliferation, and cytotoxic T lymphocyte activity, and are efficiently broken down by dehydrogenase and decarboxylase enzymes produced by immune cells. (4)

Finally, BCAAs and aromatic amino acids share the same transport protein into the brain (Trp, Tyr, and Phe).

They may have a function in protein synthesis, neurotransmitter synthesis, and energy generation once they reach the brain. (4)


Leucine is a branched-chain amino acid that, like valine, is essential for protein synthesis and muscle repair.

It also aids in blood sugar regulation, wound healing, and the production of growth hormones. (1)


Isoleucine: The third and final branched-chain amino acid, isoleucine plays a role in muscle metabolism and is found in high concentration in muscle tissue.

Immune function, haemoglobin synthesis, and energy control are all dependent on it. (2)


Valine is one of three branched-chain amino acids, which means that one of its chains branches out to one side of its molecular structure.

Valine is involved in energy production and helps to promote muscle development and repair. (3)

How They Work

BCAAs are mainly oxidised in the skeletal muscle and other peripheral tissues, unlike other amino acids, which are oxidised in the liver. (4)

The effects of BCAAs on muscle growth in rats were investigated.

It was discovered that a mixture of BCAAs alone have the same effect on growth as a complete amino acid mixture, but an amino acid mixture containing all amino acids except BCAAs has no effect on muscle growth. (6)

Isoleucine or valine administration alone showed little impact on muscle development, while leucine administration alone seems to be almost as beneficial as the full BCAA combination.

Leucine promotes the formation of the eIF4F complex and indirectly activates p70 S6 kinase.

The mTOR signalling pathway (a major regulator of muscle growth) contains P70 S6 kinase, which has been demonstrated to enable hypertrophy and recovery of muscle (in animal studies).

A resistance exercise session without BCAA supplementation has no effect on mTOR phosphorylation and even causes a reduction in Akt phosphorylation after resistance training.

The phosphorylation of p70 S6 kinase has been found in certain cases.

Following a training session, sufficient phosphorylation of p70 S6 kinase and S6 showed that the signalling cascade had been activated.

I'll discuss BCAAs effects on muscle growth further down.

Benefits & Effects

BCAAs may have a multitude of benefits, however there are some very mixed results from studies.

I'll take a deep-dive into the research and see whether BCAAs are actually beneficial or if they are a waste of money.

Power Output (Strength)

Mixed effects on power production are seen, although when it does occur, it is due to decreased muscle soreness after repeated exercise rather than a direct increase in power output.

This may be due to anti-fatigue benefits rather than an increase in power production. (7)

From the research that has been conducted, it seems that BCAAs have no direct beneficial effect on strength improvement and instead any strength improvement may be from their beneficial effect on reducing fatigue and muscle soreness.

Muscle Growth

BCAAs, particularly leucine, have the theoretical ability to enhance muscle growth, however some studies suggest that supplementing with leucine, isoleucine, and valine sometimes decreases protein synthesis.

This is strange, I researched why this may be the case.

It turns out that all amino acid precursors must be available for a physiologically meaningful increase in the rate of muscle protein synthesis.

Muscle protein breakdown produces intracellular free EAAs that are ready to be incorporated into protein synthesis.

Approximately 70% of EAAs produced by muscle protein breakdown are reincorporated into muscle protein under normal circumstances.

The efficiency of returning EAAs from protein breakdown to muscle protein can only be improved to a certain degree.

Because of this, a dietary supplement of BCAAs cannot sustain an enhanced rate of muscle protein synthesis on its own.

The other EAAs' availability will quickly become a rate limiting factor for increased protein synthesis.

The few human investigations that have been done so far have shown that when BCAAs are consumed, muscle protein synthesis reduces rather than increases.

This leads me to conclude that BCAA supplements do not enhance muscle anabolism on their own and instead must be combined with a source of EAAs / protein.

Adverse Effects & Safety

When taken by pill, liquid, or powder form, branched-chain amino acids are likely safe for consumption.

Tiredness and a reduction in coordination can occur with supplementation of BCAAs. Before or during tasks requiring motor coordination, such as driving, branched-chain amino acids should be taken with caution.

Nausea, vomiting, diarrhoea, and stomach bloating are all possible adverse effects of branched-chain amino acids.

They may also induce elevated blood pressure, headaches, and even skin whitening in rare instances.

There isn't enough trustworthy evidence to determine if branched-chain amino acids are safe to consume during pregnancy or breast-feeding.

To be on the safe side, avoid using it if you're pregnant or breastfeeding.


Listed below are the known interactions of branched-chain amino acids with specific diseases and medications, etc.

  • Amyotrophic Lateral Sclerosis (ALS, Lou Gehrig disease): Branched-chain amino acids have been related to lung failure and increased mortality rates in people with Amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig disease). If you have ALS, avoid using branched-chain amino acids.

  • Branched-Chain Ketoaciduria: Consumption of branched-chain amino acids can cause seizures and severe mental and physical impairment. If you have this disease, avoid using branched-chain amino acids.

  • Diabetes: Branched-chain amino acids may alter blood sugar levels. Blood sugar is also controlled using diabetes medicines. If you combine BCAAs with diabetic medication, your blood sugar may drop too low. To be safe, avoid taking BCAAs if you have diabetes and take any type of diabetes medications.

  • Levodopa: Branched-chain amino acids may reduce the amount of levodopa absorbed by the body, reducing the efficacy of levodopa. BCAAs and levodopa should not be taken at the same time.

  • Diazoxide (Hyperstat, Proglycem): Branched-chain amino acids are utilised in the body to aid in the production of proteins. When Diazoxide is combined with BCAAs, the effects may be reduced. More information regarding this interaction is required and should be avoided.

  • Corticosteroids: Branched-chain amino acids are utilised in the body to aid in the production of proteins. When corticosteroids are combined with BCAAs, the effects may be reduced. More information regarding this interaction is required and should be avoided.

  • Thyroid Medications: Branched-chain amino acids aid in the production of proteins in the body. Some thyroid medications may reduce the breakdown of BCAAs in the body. More information regarding this interaction is required and should be avoided.


The three BCAAs are leucine, isoleucine, and valine. They’re considered the most anabolic of the nine EAAs. However, leucine taken alone may be more anabolic than if it's taken with isoleucine and valine, due to competition for absorption in the gut and entry into muscle tissue.

  • The typical leucine dosage is 2-10 grams (2,000-10,000 mg)

  • The typical dosage for isoleucine is 48-72 mg per kilogram of bodyweight.

  • The typical dosage of combined BCAAs is around 20 grams (20,000 mg), with a balanced ratio of leucine and isoleucine.

BCAA supplementation is not necessary if enough BCAAs are provided through the diet. Further research is needed to determine valine’s optimal dosage and effects of supplementation.

Note: It seems as though BCAAs taken alone is not effective and may in fact be detrimental, this is why we recommend the consumption of EAAs alongside BCAAs or leucine.

Other Dosages

Below is the dosage of BCAAs used for other applications, such as liver disease and a movement disorder caused by antipsychotic drugs.

  • For reduced brain function in people with advanced liver disease (hepatic encephalopathy): 240 mg/kg/day (up to 25 grams) of branched-chain amino acids daily for three months. In some instances, the dosage is split into three daily doses.

  • For a movement disorder often caused by antipsychotic drugs (tardive dyskinesia): Three times daily for three weeks, a branched-chain amino acid drink comprising of valine, isoleucine, and leucine at a dosage of 222 mg/kg.

More Information

Below is more technical information about branched-chain amino acids, such as other names, functions and roles, synergies, etc.

Other Names: BCAAs, BCAA

Primary Role: Exercise performance, muscle gain

Confused With: Leucine, Isoleucine, Valine

Things to Note

  • Although BCAA supplementation has been claimed to have a stimulatory effect, the placebo effect cannot be ruled out as a reason owing to a lack of study on the subject.

  • BCAAs are believed to be ineffective and possibly detrimental to muscle growth when taken on their own, it is now recommended to take BCAAs with other amino acids (such as EAAs or a source of protein).


This section contains links to research, studies, and sources of information for this article, as well as authors, contributors, etc. All sources, along with the article and facts, are subjected to a series of quality, reliability, and relevance checks.

Real Muscle primarily uses high-quality sources, such as peer-reviewed publications, to back up the information in our articles. To understand more about how we fact-check and keep our information accurate, dependable, and trustworthy, read more about us.

This evidence based overview of branched-chain amino acids (BCAAs) features 7 references, listed below.

1. PubChem Compound Summary for CID 6106, Leucine. ✔

2. PubChem Compound Summary for CID 6306, l-Isoleucine. ✔

3. PubChem Compound Summary for CID 6287, Valine. ✔

4. Monirujjaman M. Metabolic and Physiological Roles of Branched-Chain Amino Acids. Advances in Molecular Biology. (2014)

5. Babchia N, Calipel A, Mouriaux F, Faussat AM, Mascarelli F. The PI3K/Akt and mTOR/P70S6K signaling pathways in human uveal melanoma cells: interaction with B-Raf/ERK. Investigative Ophthalmology & Visual Science. (2010, Jan)

6. Scot R. Kimball, Leonard S. Jefferson. Signaling Pathways and Molecular Mechanisms through which Branched-Chain Amino Acids Mediate Translational Control of Protein Synthesis. The Journal of Nutrition. (2006, Jan) ✔

7. Shimomura Y, Inaguma A, Watanabe S, Yamamoto Y, Muramatsu Y, Bajotto G, Sato J, Shimomura N, Kobayashi H, Mawatari K. Branched-chain amino acid supplementation before squat exercise and delayed-onset muscle soreness. Int J Sport Nutr Exerc Metab. (2010, Jun) (Randomised Controlled Trial) ✔

Citations with a tick indicate the information is from a trusted source.


The information provided in this article is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the guidance of a physician or other competent professional before following advice or taking any supplement. See our terms and conditions.

Real Muscle leads the way in terms of transparency and privacy, which is why we want to let you know that some of the outbound links in this article may be affiliate links in which we may earn a small commission through. Despite this, our product recommendations are completely unbiased.

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