Are BCAAs Essential For Muscle Protein Synthesis- Facts and Fallacies of Supplements

What are BCAAs: Branched Chain AminoAcids

Amino acids are building blocks of proteins. There are 22 amino acids in the body that carry out various functions especially protein synthesis. Among all amino acids, 9 are called Essential Amino Acids. These 9 essential amino acids must be obtained from external sources like animal food products (e.g. milk proteins).They cannot be produced in the body. Out of these 9 essential amino acids, 3 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: which means they break down into compounds that synthesize glucose. Leucine, on the other hand, is ketogenic: meaning it is degraded into constituents that make ketone bodies [1]. BCAAs make up for about one-third of muscle protein [2].

Functions of BCAAs (the three musketeers: Leucine, Valine, and Isoleucine)

  1. Protein synthesis
  2. Energy production [3]
  3. Involved (especially Leucine)  in various metabolic processes like muscle formation and repair [2].

Leucine: Everybody's favorite! 

Leucine has been most thoroughly studied because of the wide range of functions it carries out:

  1. has a high oxidation rate in comparison to its counterparts, namely Valine and Isoleucine.
  2.  stimulates protein synthesis in muscle, which makes this BCAA very attractive for further research.
  3. Leucine has been shown to be closely linked to the release of gluconeogenic precursors e.g. alanine from muscle.
  4. During exhaustive exercise, leucine concentration falls and there is a reduction in glycogen stores.

Adding leucine alone (76%) to a high protein supplement leads to

  1. a decrease in fat deposited in the abdominal cavity and near vital organs like liver, pancreas, and intestines.
  2. increases workout performance enormously
  3. repairs and leads to gain of additional muscle tissue [4]
  4. reduces the muscle soreness
  5. decreases the rate of degradation of protein
  6. has a sparing effect on glycogen stores in muscle, and
  7. might even improve both mental and physical perception

Why are BCAAs important

All amino acids other than BCAAs are broken down by the liver which are then transported to other parts of the body. However, BCAAs are metabolized by muscle which is not a gluconeogenic (or glucogenic) organ meaning it cannot synthesize glucose. Therefore, Valine and Isoleucine cannot be converted to glucose in muscle [5]. Thus, Leucine is the only BCAA that can recycle glucose in muscle [6].


Why do we feel tired after  exercise: The Scrutinizer Reveals The Mystery

There are two main factors behind fatigue during physical exercise:

  1. Peripheral Factors, and
  2. Central Factors

Both of these are affected by the nutrition, intensity and time of exercise, and the training status of the person [10].

Peripheral Fatigue: there have been numerous studies on this aspect of fatigue [11]. Some of the causes include:

  1. depletion of phosphocreatine in muscle
  2. reduction of muscle glycogen
  3. failure of neuromuscular transmission, and
  4. even buildup of protons

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

  1. depletion of liver glycogen during prolonged exercise which leads to a decrease in blood glucose levels
  2. an increase in the ratio of the concentration of free tryptophan: BCAA
  3. uptake of tryptophan (an amino acid) by the brain increases the release of neurotransmitter 5-HT (5- hydroxytryptamine) [12,12b] during sustained exercise. In other words, when BCAAs are taken up by muscle and their concentration decreases in plasma.

Why or how do BCAAs help

  1. BCAAs delay the central fatigue. As explained above the ratio of free tryptophan: BCAA increases during exercise. As a result, the levels of BCAAs decline in the plasma.Thus, if BCAAs are consumed, their levels in plasma will increase, and the ratio of free tryptophan: BCAA will become lower. This, in turn, decreases the 5-HT synthesis in brain and delays the central fatigue.
  2. BCAAs maintain glucose levels in the muscle (shown in above image), therefore, it’s important to consume a carbohydrate or protein drink during or after training to increase the insulin levels and transport BCAAs to the cells [7].
  3. BCAAs have been shown to reduce the exercise-induced muscle damage [9].
  4. Improvement in mental agility: BCAAs taken together with carbohydrates, shows improvement in mental agility during sustained competitive exercises [15].
  5. BCAAs lower the exercise-induced muscle damage and tissue breakdown in the body: 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. Thus, lower the levels of CPK and LDH, lower the level of exercise-induced muscle damage in the body [9].
  6. BCAAs exert a protein sparing effect [17] that allows the athletes to train harder during training cycles and recover faster by decreasing the exercise-induced damage [18].
  7. BCAAs improve skeletal muscle wasting even if not caused by training [19].

Timing is Everything: When to use BCAAs 

Lately, there is a plethora of literature on BCAAs and their use in sports and resistance training. There have been conflicting reports on when these amino acids should be used. Taking them both before and after the resistance training has shown an improvement in protein synthesis and thus prevent the muscle damage [14].

Recommended amounts of BCAAs 

An upper limit of 450 mg/Kg body mass/day is well tolerated [20] 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 estimate. For individual use, people will have to start from 5g/day and see the results.

Sources of BCAAs

Whey, milk proteins, beef, chicken, fish, soy proteins, eggs, baked beans, whole wheat, brown rice, almonds, brazil nuts, pumpkins seeds, lima beans, chickpeas, cashew nuts, lentils, and corn.

What is so special about Leucine?

Recent investigations have shown that Leucine is a 'hidden warrior' providing multiple benefits:

  1. Leucine is the most abundant of the three branched chain amino acids (BCAAs) in muscles (the other two are isoleucine and valine).
  2. It is the lead player in protein synthesis: thus, it has its own VIP entrance to the muscle. Once inside, it acts as an anabolic trigger. This means it enhances protein synthesis by providing an important building block. As a result, the magic happens and the process of building muscle is upregulated.
  3.  Stimulates protein synthesis: Regardless of the goal: building muscle or preventing muscle loss (during aging or dieting), the absolute key is to stimulate protein synthesis.Therefore, it is inadvisable to train or exercise during fasting or not eating afterward, as that will only cause loss of muscle (no protein, no muscle). Since BCAAs are the only amino acids metabolized in muscle, consumption of any protein with added BCAAs and especially Leucine is crucial [12]. Therefore, the most effective strategy is to supplement the diet with additional leucine to maximize muscle gain after resistance exercise.
  4. Leucine supplementation has been shown to even aid in the recovery of regenerating Tibialis Anterior Muscle (TA) when analyzed on day 10 post-injury [13].
  5. Leucine augments weight loss and preserves lean body mass:

     (a) Consuming food with high content of leucine leads to significant loss in weight and fat. In addition, it protects the  muscle from degradation and provides a better glucose control.

(b) Consuming a diet rich in Leucine, carbohydrates, and fat: also advances a significant weight loss [8], boosts better control of blood sugar, and reduces total and LDL “bad” cholesterol. This is a well-balanced diet since all three macromolecules are present together, which is ideal for a good metabolism to take place. Therefore, this is an ideal diet to consume in comparison to only a protein diet.

[Note: In recent years, there has been a significant misinformation regarding the consumption of fat and carbohydrates. The above findings and the structure of our cell membrane confirm that it is necessary to include all three macromolecules in our diet. The cell membrane is made up of both lipids and proteins (sometimes carbohydrates) which makes the lipid bilayer fluid. This fluidity is important for ions and molecules to be transported in and out of the cells. Additionally, the cell membranes have properties of both lipids and water-loving substances, which means fat is also a critical component of our diet].

6. Leucine increases resting metabolism by boosting levels of UCP3 (uncoupling protein 3). This causes the body to lose energy as heat rather than storing it as body fat.

7. Lastly, Leucine improves body composition, augments weight loss, and even corrects metabolic instabilities (e.g. elevated levels of glucose and cholesterol) [8].

Do BCAAs have side effects?

The dose recommendations in this article are for people not suffering from any pathological conditions. To the best of our knowledge from the entire peer-reviewed literature published so far on BCAAs, it seems they have no known toxicity in individuals who are healthy. However, there is no study on the long-term use of BCAAs.



Lately, supplements have emerged as vital components in the training regimen of athletes and even physical training enthusiasts to enhance their athletic performance. BCAAs are one of those supplements. However, at any given time there are thousands (30,000 approx.) of supplements crowding the shelves. Once again, confusion sets in the minds of consumer unable to decide which product is making the right promise and actually delivering it.

The aim of this article is to explain the biochemistry and metabolism of BCAAs in plain and simple language, so no one falls prey to false promises. In addition, they can make correct decisions i.e. in favor of improving their health. Taking all the peer-reviewed publications on BCAAs to date, and subjecting them to a meta-analysis validates the hypothesis that BCAAs can enhance muscle formation. The condition attached is to use at the recommended dosages and when no illnesses are present. In various health conditions, BCAAs would have interactions and the whole process would only backfire. However, I have not found any studies on long-term effects of BCAAs. This kind of study is an important study that would further provide an answer to the safety of these supplements taken every day.




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