Branched chain amino acids (BCAAs) are a group of three essential amino acids (leucine, isoleucine, and valine) that account for 35–40% of the essential amino acids in body protein, and 14–18% of the total amino acids in muscle proteins.1-3


Proteins are nitrogen-containing compounds that are vital for life. Their name refers to their importance, because the word “protein” is derived from the Greek word “protos”, meaning “primary” or “first”.

Proteins are chains of amino acids, the building blocks of tissues in the body. The human body is comprised of 16-19% of protein.26-29

In terms of human health and nutrition, there are 20 amino acids coded by our DNA and involved in protein synthesis. Nine of these 20 proteinogenic amino acids are classified as indispensable or essential amino acids meaning they cannot be synthetized in the human body from naturally occurring precursors at a rate to meet the metabolic requirement.26, 27

Of the nine essential amino acids, three are so-called branched-chain amino acids (BCAAs) (leucine, isoleucine and valine). “Branched-chain” refers to the chemical structure of BCAAs, they are the only three amino acids to possess a branched side chain.



Their main function is building blocks for the body’s protein. But, in addition to their function as structural components of proteins, BCAAs also exert regulatory control of a number of metabolic and physiological processes. These include the regulation of protein turnover, the metabolism of fats and carbohydrates, energy production, synthesis of neurotransmitter, as well as the functioning of the immune system.40

Let’s see some of the main benefits rot BCAAs regarding our performance, body composition, and health.

IMROVED PHYSICAL & MENTAL PERFORMANCE – Increase endurance capacity, muscle strength, reduce ratings of perceived exertion, and mental fatigue during prolonged exercise.

During intense exercise, and in conditions of a relative lack of energy, the metabolism of BCAA is accelerated in skeletal muscle. 1-4, 11-14 This is why BCAAs are receiving considerable attention as a helpful supplement for those who enjoy exercise and sports.2

Unlike other amino acids which are primarily metabolized in the liver, BCAAs tend to bypass the liver and pass into systemic circulation where more than 60% are utilized directly by skeletal muscle. 1-5, 9

In studies, BCAA supplementation, particularly before and/or during exercise, has been shown to improve endurance exercise capacity, skeletal muscle strength, increase resistance to fatigue, reduce ratings of perceived exertion, reduce mental fatigue during prolonged exercise, and improve cognitive performance after exercise. 2-15, 33-35

Central hypothesis of fatigue: The amino acid tryptophan is the precursor of peripherally and centrally produced serotonin. During intense physical activity, the plasma ratio of BCAAs to tryptophan is altered in favor of the latter. As BCAAs share the same transporter protein as tryptophan for transport into the brain, this decrease in plasma BCAA-to-tryptophan ration increases tryptophan uptake into the brain. That may lead to increase in synthesis of the related neurotransmitters such as serotonin, which is associated with induction of fatigue.

According to this theory, supplementation of BCAAs prior to vigorous exercise, replenishes oxidized BCAAs to preserve the BCAA-to-tryptophan ratio. This can attenuate fatigue, and may be beneficial for maintaining a high level of performance.35, 40

In addition, BCAA loading before exercising (beyond the above mentioned serotonergic mechanisms) may also reduce glycogen depletion rates and interact with ammonia in serum, a possible promoter of fatigue associated with muscle breakdown. 33-35



Decrease the net rate of protein degradation caused by heavy exercise, and promote muscle protein synthesis.

BCAA supplementation before, during and/or after exercise has been reported to decrease exercise-induced protein degradation, possibly by promoting an anti-catabolic hormonal profile. In addition, BCAA (leucine in particular), is recognized as a keystone that promotes protein synthesis by activating the so-called mTOR signaling pathway. 31, 32, 36-39 Thereby, BCAA supplementation in combination with intense training may lead to greater gains in fat-free mass.

A study from University of Verona reported that BCAA supplementation (10 grams per day) over 21-days increased fat free mass by 1.5%, while subjects ingesting a placebo had no change in muscle mass.31, 36

In another study published in the Journal of the International Society of Sports Nutrition ingestion of a supplement containing BCAAs when combined with resistance training, resulted in a greater increase in lean mass, and greater strength gains on the bench press and squat compared to placebo. This was observed even when compared to ingestion of a whey supplement or a carbohydrate based sports drink. 5



Improve fat loss, increase leptin release, energy expenditure, fat oxidation rate, and support glucose metabolism.

Dietary surveys found that higher dietary BCAA intake is associated with lower prevalence of overweight status/obesity among apparently healthy adults.42, 43

Several potential mechanisms may account for the inverse association between BCAA intake and body weight, including increased leptin production, enhanced energy expenditure, and fat oxidation rates via increased expression of uncoupling proteins, and improved insulin sensitivity.40-45

In a study from France, elite wrestlers consumed 1 of 4 energy-restricted diets comprised of high protein, high BCAA, low protein, or control diet for 19 days. Significantly, the highest body weight loss (-4 kg) and decrease in the percent of body fat (-17.3%) were observed for subjects of the high BCAA group, while there was no change in aerobic capacities, anaerobic capacities, or muscular strength.41

In another study from Brazil, researchers found that BCAA supplementation (at level of 300 mg/kg/day) for 3 days combined with an exercise-induced glycogen depletion protocol not only resulted a greater resistance to fatigue compared to the placebo, but also enhanced lipid oxidation during exercise.45



Promote recovery, and mitigate muscle soreness.

As mentioned earlier, one the main benefits of BCAAs is their ability to attenuate the breakdown of muscle proteins and mitigate consequences of surrounding muscle damage. In this regard, studies have investigated and offered support for BCAA’s ability to promote recovery, mitigate soreness and attenuate losses in force production.32

A particular study from Japan found that BCAA supplementation before exercise (at dose of 9.6 g/day) significantly suppressed delayed onset muscle soreness (DOMS) and exercise-induced muscle damage (EIMD) (measured by serum levels of creatine kinase (CK), lactate dehydrogenase (LDH), and aldolase) in the days following the exercise, compared to control group. 46



Helps keep your immune system strong, combating immunosuppression associated with highly intense physical activities.

BCAAs play an important role in the growth and proliferation of immune cells, (including lymphocytes, and neutrophils), as well as natural killer cell activity.40 Studies showed that restriction of any BCAA may impair host defense systems, while BCAA supplementation leads to higher immune parameters, and better recovery in surgery patients.40

For athletes and physically active individuals, it is also important to note that intense long-duration exercise has been associated with immunosuppression. According to related investigations, BCAAs are crucial for the maintenance of immune function under highly demanding situations. Related trials found that BCAA supplementation modified the immune suppression engendered by sport activity, attenuated higher inflammatory responses and muscle soreness induced by severe exercise, and increased the expression of genes involved in the antioxidant defense.16-20 It may reduce the fall of plasma L-glutamine concentrations that is observed after prolonged intense exercise. This reduction in plasma L-glutamine has been paralleled by an increased incidence of symptoms of infections.16-20



The richest dietary sources of BCAAs are eggs, meat, fish and dairy products, but we can also obtain them from plants. Those with the highest amounts include:30

  • Beef, round – 6.8 grams/100grams
  • Chicken breast – 5.9 grams/100grams
  • Turkey breast – 4.6 grams grams/100grams
  • Canned tuna – 5.2 grams/100grms
  • Salmon – 4.9 grams/100grams
  • Eggs – 3.3 grams/2 eggs
  • Milk – 2.2 grams/1 cup (240 ml)
  • Beans and lentils – 2.5-3 grams/1 cup depending on the variety
  • Nuts and seeds – 0.7-1 gram/28 grams depending on the variety
  • Whey protein isolate – 6.5 grams/1 serving (30grams)
  • Soy protein isolate – 5.5 grams/1 serving (30grams)
  • Wheat protein isolate – 4.5 grams/1 serving (30grams)



Optimal dosage of BCAAs before and/or during training may be between 5-12 grams of combined BCAAs (0,1 grams/kg of bodyweight).

This may help minimize protein degradation and lead to greater gains in (or limit losses of) fat-free mass, while improve exercise performance, as well as psychological perception of fatigue.

In addition, as mentioned earlier, leucine has been shown to play a unique role in stimulating muscle protein synthesis, serving as a signal to initiate the rate-limiting translation initiation step of muscle protein synthesis.

Thus, after workout leucine may exert additional beneficial effects to improve muscle protein synthesis, and recovery, when provided in the correct amounts (i.e. 3–6 grams).

It should be noted that although BCAAs exhibit the capacity to stimulate muscle protein synthesis, a full spectrum of essential amino acids could be necessary to stimulate a maximal response of protein synthesis following exercise, and thus facilitate skeletal muscle hypertrophy in response to resistance exercise training. According to clinical investigations, ingestion of BCAAs promoted a 22% greater increase in muscle protein synthesis compared to a placebo. The reported rates , however, were 50% lower than what was found when a dose of whey protein containing similar amounts of BCAAs was consumed.22-25

In summary, oral supplementation with BCAA following exercise stimulates protein synthesis more potently than ingestion of leucine alone, but not as effectively when full spectrum of essential amino acids is provided.

Thus, after a workout, it is best to opt for a source that contains the full spectrum of essential amino acids, with at least 3-6 grams of leucine (0,05 grams/kg of bodyweight). In addition, supplement with a combined BCAA or a leucine formula if needed.

It has also been noted that although only an optimal dose of a complete protein or a full spectrum of free form essential amino acids can sustain and maximize exercise-induced rates of muscle protein synthesis, a suboptimal dose of intact protein with additional leucine has been shown to increase the response of muscle protein synthesis equivalent to an optimal protein dose at rest. 22-25


References ▼