Branched Chain Amino Acids (BCAAs) – All you need to know


BCAA stands for Branched Chain Amino Acids because of their chemical structure or formula. Each amino acid (as the name shows) has an amino group (NH2) and an acid group (COOH), and rest in between is a chain of groups like ––CH2 defines the name and function of the particular amino acid. Of all the amino acids (there are 22 in total), only 3 are called Branched Chain Amino Acids, namely Valine, Leucine and Isoleucine. These three amino acids have a branched chain rather than a linear chain thus the name.


Exercise leads to a depletion of liver glycogen and muscle glucose levels decrease. BCAAs are the only amino acids that are metabolized in muscle and go direct to circulation. The rest of the amino acids are metabolized in liver. BCAAs delay central fatigue and maintain glucose levels in muscle. They also delay exercise induced muscle damage and tissue breakdown. BCAAs let the athletes train harder because of their protein sparing effect.


BCAA supplementation is beneficial in relation to sports and exercise. The requirement of BCAAs is increased after exercise due to muscle degradation. Thus, athletes or even people exercising regularly would benefit from BCAA supplements. BCAA supplementation, before and after exercise promotes muscle protein synthesis and decreases exercise related muscle damage. However, the results for endurance performance with BCAA are inconsistent and are more for sprinting or weight training.


Numerous toxicity studies have been performed in rats and mice, however no toxicity has been reported with BCAA supplementation. There have been no reports on BCAA related toxicity in sports and exercise.


  • Pregnant and lactating women
  • Anyone who is on medication for illnesses like diabetes, high blood pressure, Parkinson’s and so on
  • Children under the age of 16yrs





Amino acids are building blocks of protein. There are 22 amino acids that are required in the body to carry out various functions especially protein synthesis. Among all amino acids, 9 are called essential amino acids as they are not produced in the body and must be obtained from external sources like animal food products (e.g. milk proteins). Out of these 9 essential amino acids, three are called branched chain amino acids (BCAAs), named as such because of their chemical formulae, these three are: Leucine (Leu), Isoleucine (Isoleu) and valine (Val).

Of the three BCAAs, isoleucine and Valine are glucogenic (make precursors to synthesize glucose) and leucine is ketogenic (makes precursors for ketone bodies and fatty acid synthesis)1. BCAAs make up for about one-third of muscle protein2. They are involved in protein synthesis and energy production3, thus BCAAs (especially leucine) have important function in various metabolic processes like muscle formation and repair 2. It has been shown that adding leucine (76%) to a high protein supplement leads to reduction of visceral fat, high-level performance, repairing and building of muscle tissue4.


All amino acids other than BCAAs are broken down by liver and then transported to other parts of the body. However, BCAAs are metabolized by muscle and muscle is not a gluconeogenic organ meaning it cannot synthesize glucose. Therefore, valine and isoleucine cannot be converted to glucose in muscle5, rather leucine is the only BCAA that can recycle glucose in muscle6.


Fig 17: shows leucine gets converted to alanine in the skeletal muscle. Alanine then reaches liver where it is converted again to glucose. This is calledglucose alanine cycle. However, in low energy state, leucine augments glucose stimulation via getting converted to glutamate, which is then converted to alanine and thus re-synthesizes glucose. This mechanism keeps a stable glucose supply when there is low insulin and less available energy8,9. At the same time, leucine can stimulate insulin secretion and protein synthesis when enough energy is available. This insulin then enters the glutamate pathway thus modulating the glucose metabolism. Thus, leucine is the only BCAA that can control glucose metabolism via both insulin and non-insulin pathways10. At the same time, BCAAs are all unique as they are metabolized in muscle where they can be broken down when energy is needed quickly.


There are two main factors behind fatigue during physical exercise:

Peripheral and Central factors.

Both of these are affected by the nutrition, intensity and time of exercise, and the training status of the person.

Peripheral fatigue: There have been numerous studies on this aspect of fatigue. Some causes described are depletion of phosphocreatine in muscle, reduction of muscle glycogen, failure of neuromuscular transmission and even buildup of protons11.

Central fatigue: Two main reasons have been described for central fatigue.

  • There is depletion of liver glycogen during prolonged exercise leading to a decrease in blood glucose levels
  • The other factor is increase in the ratio of concentration of free tryptophan / BCAA, uptake of tryptophan (an amino acid) by the brain and increase in the release of neurotransmitter 5-HT (5 hydroxy tryptamine)12, 12b during sustained exercise. In other words, BCAAs are taken up by muscle and their concentration in plasma becomes less.


As explained above the ratio of free tryptophan/BCAA increases during exercise, therefore, if BCAAs are consumed, then their levels in plasma will increase, which in turn reduces the free tryptophan/BCAA ratio. This in turn decreases the 5-HT synthesis in brain delaying the central fatigue. In addition, BCAAs maintain glucose levels in the muscle (Fig 1), therefore, it’s important to take a carbohydrate or protein drink during or after training to increase the insulin levels and thus transport of BCAAs in cells. However as explained above, leucine is the lead player in protein synthesis, thus building muscle. Therefore, it is inadvisable to train or exercise during fasting or not eating afterwards, as that will only lead to muscle loss. Leucine supplementation has been shown to even aid in the recovery of regenerating Tibialis Anterior Muscle (TA) when analyzed on day 10 post injury13.

There has been quite a bit of literature lately on BCAAs and their use in sports and resistance training. BCAAs have been shown to reduce the exercise induced muscle damage. There have been conflicting reports on when these amino acids should be used. However, taking them both before and after the resistance training has shown an improvement in protein synthesis and thus prevent the muscle damage14. It has also been reported that the use of BCAAs taken together with carbohydrates, shows improvement in mental agility during sustained competitive exercises15. In addition, BCAAs have been found to decrease the serum levels of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH)16 , which are indicators of muscle damage and tissue breakdown. This shows that BCAAs lower the exercise induced muscle damage in the body. Literature also shows that BCAAs exert a protein sparing17 effect that allows the athletes to train harder during training cycles. This allows for greater recovery time by decreasing the exercise-induced damage18. Recent studies have also shown involvement of BCAAs in improving skeletal muscle wasting even if not caused by training19.


An upper limit of 450 mg/Kg body mass/day is well tolerated20 and is not advisable to increase this limit as it would stress the kidneys and could lead to deleterious effects. Similarly, an upper limit of leucine has been reported as 500mg/Kg body wt/day or an approximation of about 35g/day is a cautious estimate21. For individual use, people will have to start from 5g/day and see the results.


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