The effect of BCAA: what these amino acids do and how they work

Die Wirkung von BCAA: Was diese Aminosäuren tun und wie sie wirken

In this article you will learn everything you need to know about BCAA. for Branch Chained Amino Acids. In this article we explain what is special about these amino acids, how BCAAs work in the body and what the current state of knowledge on the subject of BCAAs is.

You will learn why the effects of BCAA are important for certain body processes and how these processes affect training and muscle building.

We take into account studies that consider possible side effects. You will also learn what effect BCAAs have on losing weight and which foods are rich in BCAAs.

the essentials in brief

  • BCAA stands for the three essential amino acids leucine, isoleucine and valine. They are made available to the body exclusively through food and are important for metabolism, gut health and the immune system (4)
  • Due to the continuous build-up and breakdown of proteins in our cells, BCAA is always present in our body's amino acid pool with appropriate nutrition. BCAA in the form of capsules and powder is therefore only useful in special cases
  • Increased BCAA burning increases the amount of glutamine in muscle tissue, leading to the belief that BCAAs promote muscle growth. However, studies refute this effect and even prove the opposite (9)

The effect of BCAA: questions and answers about what BCAA is and what these amino acids do

In particular, the effect of BCAA as a supplement raises doubts in many people. The overarching question is often how effective or necessary BCAA supplements are, whether they change the body and psyche and what effects they have on our metabolism. What are BCAA and why do we need them? We answer these and other questions in this article.

What are BCAAs?

BCAA describes a group of amino acids that are found as part of the proteins in our cells (1). This particular group consists of the amino acids leucine, isoleucine and valine. These proteinogenic (protein-building) amino acids have a branched-chain structure, from which the English abbreviation BCAA (branch chained amino acids) is derived.

  • Leucine: is a proteinogenic α-amino acid. It crystallizes in white flakes, which is where the name comes from
  • Isoleucine: in its natural L form, is an essential proteinogenic α-amino acid
  • Valine: in its natural L form, is an essential proteinogenic α-amino acid found in small amounts in all major proteins

In contrast to most amino acids, BCAAs are largely stored in the skeletal muscles and are mainly found in muscle tissue and blood plasma, but also in the brain. About 70 percent of the increase in free amino acids in the blood plasma after a meal is due to BCAAs (2).

How do BCAAs work in the body?

In the intestine, BCAA are absorbed through the intestinal mucosa (2) and reach the target tissue directly through the blood. They play an important role in regulating energy homeostasis, nutritional metabolism, gut health, and the immune system (4).

BCAA have a special function for protein biosynthesis, which is responsible for cell healing or cell formation. Protein biosynthesis can only take place if our body receives protein that has a complete amino acid profile. Proteins are complete when essential amino acids are in the correct ratio to other amino acids (3).

Why are essential amino acids important?

Essential amino acids are so important to us because the body does not produce them itself, which means they have to be supplied to the body through food so that they accumulate in our cells.

In addition to the branched-chain amino acids, BCAAs also belong to the group of essential amino acids. “essential amino acids” (EAA) and are the most common essential amino acids.

A complete amino acid profile is necessary for protein biosynthesis to function in the body. If we do not add BCAAs to our body through food, our amino acid profile is incomplete and protein biosynthesis, which is responsible for cell formation and cell healing, does not take place.

When do BCAAs work in the body?

Due to the continuous build-up and breakdown of proteins in our cells, there is always enough BCAA in our amino acid pool, which we replenish through our diet and through the body's own processes throughout the day.

With this in mind, it doesn't matter when we take BCAAs, as our bodies always have enough essential amino acids with the right diet (5).

muscle training

BCAA supplements are commonly used in muscle training because of their effects (Image source: Anastase Maragos / Unsplash)

Since BCAAs, in contrast to other amino acids, reach the tissue directly via the blood, they act more quickly than other amino acids, which, like whey proteins for example, only reach the bloodstream via the liver with a delay.

That's why athletes who do intensive weight training like to use BCAA supplements before training. They suspect that the daily requirement for protein-building BCAAs is increased by the training and that the body does not have enough of these amino acids available during the workout due to the training intensity.

What effect do BCAA have on muscle building?

Studies consistently point out that BCAAs are an important source of energy for muscles (6). The effect BCAAs have on muscle building can be explained with protein biosynthesis, which, as mentioned at the beginning, is responsible for cell formation and cell healing in the body.

Increased BCAA burning is associated with increased synthesis of glutamine, which is secreted by muscles and makes up the major part of the amino acid pool in blood plasma at 20 percent (10). The increased amount of glutamine in muscle tissue is taken as a signal by the body to build more muscle (2,8).

The effect of BCAA in muscle building is controversial.

When BCAAs are broken down naturally in the cells, branched-chain, non-essential keto acids are also produced as an amino acid metabolism product that inhibit muscle breakdown. However, studies have shown that taking BCAAs can do the exact opposite, reducing muscle protein synthesis and protein breakdown, which means a reduction in muscle protein turnover (9).

According to another theory, the BCAA amino acid leucine should have a stimulating effect on protein biosynthesis in the mTOR gene, which is located in the muscle cells. According to one study, taking BCAAs alone increased post-workout stimulation of mTORC1 signaling (3). Other studies have already refuted this assumption (9).

How do BCCA affect training?

It has been scientifically proven that BCAAs have an effect on body and mind during and after training, with relevant studies relating primarily to endurance sports.

A clinical study of young college-age men demonstrated that BCAA supplementation during prolonged muscle endurance training reduces muscle damage (10). However, there is no scientific evidence that BCAAs improve physical recovery after endurance training (11).

At the beginning of the article it was already mentioned that BCAAs also get into the brain. Against this background, the effect of BCAA is attributed to a reduction in mental exhaustion during muscle training.

According to the current state of science, the brain messenger substance serotonin is responsible for the exhaustion processes associated with physical exertion (6).

Serotonin is made in the brain from tryptophan, which in turn competes for the same transport mechanism as BCAA. Now, when BCAA are ingested, these amino acids take away the vehicle from serotonin. This, in turn, according to this theory, leads to less fatigue (12).

What are the advantages of BCAA in the effect as a supplement?

BCAAs occur naturally in the foods we eat every day. The rule of thumb is that foods that contain a lot of protein are also rich in BCAA in almost all cases. Fish and meat in particular are excellent sources, but so are nuts, grains and legumes.

Our food determines our amino acid profile.

It is important for protein biosynthesis that our amino acid profile is complete. We can only achieve this if we take in all the essential amino acids through our food. In addition, the value of the food is also important, which indicates what percentage of the protein from the food can be converted into the body's own protein.

The table below gives you an initial overview of different foods in terms of BCAA amounts, biological value and amino acid profile.

Groceries Valine (g) per 100 g Leucine (g) per 100 g Isoleucine (g) per 100 g biological value Complete amino acid profile
rice 0.5 0.7 0.3 81-83 No
whey protein 6.2 11.6 7.0 104-110 Yes
whole egg 1.1 1.3 0.7 100 (reference value) Yes
Salmon 1.4 1.8 1.0 75 No
Peas 1.2 2.3 1.9 56 No

As you can see, only a few foods have a high biological value. So that you increase this, the combination of different foods is necessary. For example, legumes should be combined with beans and grains or rice with beans and nuts . This increases the biological value and also creates a complete amino acid profile.

Protein foods like salmon

Protein-rich foods are almost always rich in BCAAs (Image source: congerdesign / Pixabay)

So why take additional BCAA supplements? Very easily. On the one hand, taking these aminos in capsule or powder form has the advantage that the ratio of leucine, valine and isoleucine is in an ideal ratio (2:1:1 or 4:1:1). On the other hand, BCAA supplements offer advantages for vegans, who do not always achieve a complete amino profile with purely plant-based protein sources.

What side effects do BCAA supplements have?

BCAA has been shown to be present in muscle tissue, blood plasma and the brain. But does the supplemented intake of BCAAs negatively affect our body and mind? The fact that the effect of BCCA in the brain leads to reduced fatigue after intensive training may be positive (12), but we will also show you which side effects are currently known or are still unclear.

No study of BCAA intake has found that any dosage could have adverse effects on the brain. However, it has been proven that BCAAs increase the ArAA concentration in the brain. The functional effects of such neurochemical changes include altered hormone function, blood pressure , and mood state (13).

BCAA stimulate protein synthesis and inhibit protein breakdown in skeletal muscle and the liver . With this in mind, many nutritionists are arguing that future studies of BCAA adverse effects should focus more on insulin sensitivity, kidney function, and tumor growth, rather than changes in muscle tissue, as is often the case (8).

Do BCAAs have an effect on weight loss?

There is currently no scientific evidence of a direct connection between BCAAs and their effect on fat burning, except in specific cases of people with low glycogen deficiency during exercise (17). In one study, participants on a calorie-restricted diet failed to find that strength training maintained lean body mass by taking BCAA supplements (5).

Nevertheless, the effect of BCAA capsules and powder can help you lose weight, because the supplements are isolated amino acids that, unlike complete proteins, contain hardly any calories. In this way, your body gets these valuable essential amino acids without additional fats and carbohydrates.

Unlike fat burning, BCCA's inhibitory effect on muscle breakdown is well known but controversial (9). Many use this supposed effect when losing weight by considering how your body responds to a diet. A little digression on this:

Due to the reduced calorie intake, your body accesses muscles for energy. This breaks down muscles. However, muscles burn more calories than other cells. An excessively reduced calorie, short-term diet therefore often leads to the yo-yo effect.

The inhibition of muscle breakdown by BCAA is intended to counteract this effect. On the other hand, a cyclical intake of carbohydrates, such as carb cycling , is healthier than a "BCAA diet", in which the proportion of carbohydrates is adjusted to daily use.


The long-term effects of BCAA supplements on the body and mind are not fully understood. However, it has been proven that BCAAs stimulate processes in the body and psyche that lead to reduced exhaustion after training and weaken muscle damage during muscle endurance training.

While the inhibitory effect of BCAA on muscle breakdown is often used as an argument for including BCCA in diets, studies have cast doubt on this (9). However, BCCA is useful as a supplement if your diet requires it, especially if you are deficient in leucine, valine and isoleucine. This is often the case when you follow a vegan diet.


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  5. Dieter BP, Schoenfeld BJ, Aragon AA. The data do not seem to support a benefit to BCAA supplementation during periods of caloric restriction. J Int Soc Sports Nutr. 2016 May 11;13:21. doi: 10.1186/s12970-016-0128-9. PMID: 27175106; PMCID: PMC4865017. Source
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