Branched-Chain Amino Acids: What Are They?

There are nine essential amino acids, ‘essential’ meaning that our bodies cannot synthesize them endogenously. Therefore, we must obtain them from food or supplements.

Among these nine, three amino acids are especially popular in the supplements market; leucine, isoleucine, and valine. Collectively, they are known as the branched-chain amino acids (BCAAs), a name that stems from their distinctive chemical structures.

These molecules have many biological functions, and it is crucial to consume enough each day. This article explores the best-studied BCAA benefits, uses, side effects, and more.

Uses and Benefits

The BCAAs make up around 40% of our daily amino acid requirements. They have many vital functions and play a role in the following processes:

  • Protein synthesis
  • Energy production
  • Nutrient metabolism
  • Gut health
  • Immunity

They can also be useful as biomarkers for various diseases. For example, BCAA levels tend to be altered by insulin resistance, diabetes, cardiovascular disease, and some forms of cancer.


However, one of the most common BCAA uses is in workout supplements. Many professional and recreational athletes take BCAAs either before or after training. The purported benefits include:

  • Increased energy production
  • Reduced muscle fatigue
  • Increased protein synthesis, leading to muscle gain
  • Enhanced recovery from intense exercise

Leucine is thought to be particularly important as it directly stimulates protein synthesis. It also appears to promote insulin release, increasing cells’ uptake of glucose for energy production.

Therefore, it reduces the amount of muscle tissue that the body needs to burn as fuel, thus preventing muscle breakdown.

Unfortunately, though, research on the subject has produced inconsistent results, making the benefits of BCAA supplementation less clear.

One 2018 study found that taking BCAAs before and after exercise reduced the severity of delayed-onset muscle soreness (DOMS). However, the authors concluded that the effects on muscle damage were likely negligible.

Other research has indicated that taking the BCAAs alone is of limited benefit. The reason for this is that all nine essential amino acids are necessary for muscle synthesis.

A lack of amino acids during exercise causes the body to extract them from muscle to meet its needs. Therefore, according to one 2017 publication, taking BCAAs alone could actually lead to muscle breakdown rather than gains.

It seems that there could be several other downsides to taking a BCAA-only supplement. We will discuss these in more detail below. 

Side Effects

BCAAs can compete with other amino acids for uptake in the body, specifically, the aromatic amino acids; phenylalanine, tyrosine, and tryptophan.

Aromatic amino acids play a role in producing signaling chemicals, including the neurotransmitters serotonin, dopamine, and norepinephrine.

Therefore, competition between them and BCAAs could affect neurotransmitter synthesis, impacting brain function and behavior.

Of particular interest is the fact that BCAAs share a transporter with tryptophan, the precursor to serotonin. In fact, reduced serotonin production has been proposed as one of the ways in which BCAAs counter exercise-induced fatigue.

Some experts suggest taking a B3 supplement alongside high-dose BCAA supplements to prevent deficiency.

Tryptophan also acts as a precursor to vitamin B3 (niacin). Therefore, some experts suggest taking a B3 supplement alongside high-dose BCAA supplements to prevent deficiency.

Research on mice indicates that several other BCAA side effects could occur when taken as a standalone supplement. Animals that ate a diet with a high ratio of BCAAs to other amino acids had increased appetites, a tendency toward obesity, and shorter lifespans.

Further research is necessary to determine the effects of long-term, high-dose supplementation on humans. However, it seems that most people can tolerate doses far higher than the average dietary intake without adverse effects. 


The recommended daily intake for the three BCAAs is as follows:

  • Leucine: 4g
  • Isoleucine: 2.2g
  • Valine: 2g

However, it is advisable to take these amino acids together rather than individually. Therefore, the recommended daily BCAA dosage is 8.2g for all three combined.


Research suggests that long-term supplementation with doses above this amount could alter laboratory parameters and potentially lead to complications. 

Branched-Chain Amino Acid Supplementation

Many foods contain BCAAs, including meat, fish, eggs, dairy products, legumes, whole grains, nuts, and seeds. Therefore, most people can meet their nutritional needs by eating a varied diet and focusing on high-protein foods.

However, some people, especially athletes, may choose to take a supplement either pre-or post-workout.

Whey powder is a popular choice and is an excellent source of BCAAs. However, it is unsuitable for people following a vegan diet and those with milk allergies or intolerances. Plant-based protein powders tend to have lower levels of BCAAs but are rich in several other essential amino acids.

Some supplements feature the BCAAs alone, while others contain a full range of amino acids.

There are also numerous other amino acids supplements available, either in powder or capsule form. Some feature the BCAAs alone, while others contain a full range of amino acids. As we discussed earlier, the latter option may be more beneficial for muscle gain and general health.

Finally, it is essential to conduct thorough research when purchasing supplements to find a safe and reliable product. We’ve listed some of our favorite brands in our review: What Are the Best Amino Acids? Our Top Picks 

Summary on BCAAs

Leucine, isoleucine, and valine are collectively known as the branched-chain amino acids.

These are three of the essential amino acids we require to maintain good health. They have a range of critical functions in the body and are especially important for energy production and protein synthesis.

They are common ingredients in supplements, especially those geared toward athletes. However, the current evidence suggests that taking a full range of amino acids is safer and more beneficial than BCAAs alone.

Therefore, individuals looking for an effective product should choose carefully. If in any doubt, discuss the options with a qualified dietician or another healthcare professional.

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