Written by Ben Carlisle
Last updated on: Sep 17, 2022
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Branched Chain Amino Acids (BCAAs) are a popular supplement taken by fitness enthusiasts, bodybuilders and athletes. This supplement can help improve muscle growth, recovery and endurance. But what are BCAAs? How do they work, and are they the right supplement for you?
Branched chain amino acids are three of the nine essential amino acids which the body cannot produce on its own, leucine, isoleucine, and valine. They aid the body with several functions which affect athletic performance. This includes muscle growth, fatigue, recovery, and even cognitive functionality.
For this reason the branched chain amino acids are extensively used by individuals to enhance their performance at the gym, in competitive sports, and even for weight loss programs. But what is it about BCAAs which makes them so important? Let’s take a look at the three BCAAs individually to understand them in more detail:
Branched chain amino acids provide the body with a natural means to enhance the process of muscle protein synthesis (13). These three amino acids are part of the group of nine amino acids considered the essential amino acids. They are called branched chain amino acids because of their structure. This includes a "side chain" of 1 carbon atom and 3 hydrogen atoms, which gives a branch like appearance. Supplementing with BCAAs can enhance several of the body’s functions which can improve both athletic and exercise performance.
Leucine is a branched chain amino acid (BCAA) which plays a major role in regulating muscle protein synthesis. Following a workout, the body will synthesise protein at a slower rate than the breakdown of protein. This negative balance occurs due to several factors which cause muscle protein synthesis to be inhibited (1). For the recovery of protein synthesis the body requires dietary protein or branched chain amino acids to increase tissue levels of leucine.
This is the reason why taking a supplement which contains leucine leads to several changes in the body due to reduced intercellular leucine concentrations and mTOR activation, a protein complex that limits eIF4E and eIF4G. Limiting the formation of the eIF4E and eIF4G complex leads to an increase in protein synthesis. By increasing the levels of leucine in your body, post-exercise protein synthesis is stimulated (1).
Isoleucine plays a critical role in maintaining your immune system’s basic functions (2). Studies show isoleucine is a key determinant of physiological functions throughout the body, such as growth, protein metabolism, immunity, fatty acid metabolism, and glucose transportation. The branched chain amino acid (BCAA) isoleucine can also improve the immune system via immune organs, cells, and reactive substances. And by increasing the expression of β-defensins, administering isoleucine can restore some pathogens’ effects on your basic health indicators (2).
The branched chain amino (BCAA) acid valine stimulates muscle growth and tissue repair (17). Valine can help delay fatigue as it competes with tryptophan for transportation to the brain, decreasing brain 5-HT synthesis (3).
5-HT, also known as serotonin, can create the feeling of fatigue during exercise, and the presence of valine will delay its release. The reason for this is 5-HT will be released at a later stage, this will enable an individual to maintain a higher output for a longer period during physical exercise. This will ultimately lead to better results and improved performance (3).
Now we have explained each branched chain amino acid, let’s take a look at how they can improve your performance during exercise:
During exercise, there is an increase in the brain’s tryptophan levels, which leads to the synthesis and release of 5-HT. 5-HT causes fatigue, and your body will struggle to continue exercising at its current rate. However, a study on BCAAs and central fatigue (5) showed the oral intake of BCAAs may reduce tryptophan levels by competing with tryptophan for transportation through blood cells to the brain. This means taken a supplement with these 3 amino acids will reduce the 5-HT synthesis and therefore delay fatigue.
Another study on found BCAA supplementation would lead to a lower rate of perceived exertion (RPE, which allowed the study participants to sustain higher workouts, which increased training impulse (TRIMP) and time to exhaustion (TTE) (6). In other words, BCAAs reduce the perception of physical exertion, which allows individuals who take it to handle higher workloads and to feel exhaustion far later than they would without supplementation.
Your body’s muscle mass is determined by the rate of muscle protein synthesis and the rate of muscle protein breakdown. BCAAs activate key enzymes which stimulate muscle protein synthesis after your workout. Leucine, in particular, can have anabolic effects which increase the rate of protein synthesis and reduce the rate of protein breakdown in resting muscles. This is also observable during endurance exercise (7). These effects occur due to the changes to signalling pathways which control protein synthesis.
BCAAs have been identified as an effective supplement for muscle recovery and immune regulation when combined with regular exercise (8). Supplementing your exercise routine with BCAAs before and after your workout decreases exercise-induced muscle damage (EIMD) and promotes muscle protein synthesis. This includes the reduction of delayed onset muscle soreness (DOMS) (8).
This means the effects of muscle soreness, which occur between 24 and 48 hours after a workout, which can inhibit your performance, will be reduced and, therefore, allow you to get back into the gym, performing at your optimal levels within a shorter timeframe.
As is the case with muscle preservation, how BCAAs activate key enzymes in protein synthesis and reduce the rate of muscle degradation will enable you to grow your muscle mass faster and more resiliently through the anabolic effects they have during recovery (7).
Additionally, when BCAAs are taken in conjunction with a low dose whey protein supplement, they stimulate postprandial muscle protein synthesis. However, whey alone was able to sustain increased rates of muscle protein synthesis post-exercise. This means it may be the supplement most suited to increase exercise-induced muscle protein accretion. This is likely due to containing all of the essential amino acids (9). Therefore, to maximise muscle growth whey supplementation taken alongside BCAA supplementation may be the best approach.
Studies have shown that BCAAs play a role in reducing central fatigue (10). Supplementation can improve cognitive functionality after extended periods of activity in endurance sports. They decrease mental fatigue and perceived exertion.
While the mechanisms behind central fatigue are relatively hard to examine, multiple factors have been identified to cause peripheral fatigue while exercising. Changes in 5-HT or serotonin levels are one such factor. The presence of leucine, isoleucine and valine limits the rate at which the body transports tryptophan across the blood-brain barrier, which is transported through the same carrier system that transports BCAAs.
This means there will be a reduced or delayed release of 5-HT and an increased plasma concentration. In addition to this, due to the lower perceived exertion during exercise, athletes have more capacity to focus mentally, as exemplified by a study of athletes before and after a 30km cross country race (10).
Ingesting BCAAs has been found to increase post-exercise stimulation of myofibrillar muscle protein synthesis and mTORC1 signalling. A study found BCAA supplementation after resistance exercise resulted in muscle protein synthesis being raised by 22% (11).
Furthermore, leucine aids in producing the optimal rates of protein synthesis during recovery periods (1), which leads to a positive protein balance, making it possible to grow muscle mass at an optimal rate.
A study on the effects on myofibrillar protein synthesis after resistance exercise shows whey protein should be taken as a fuel for this process and yield optimal outcomes to maximise the effects of protein synthesis, this is likely due to whey containing all nine essential amino acids (9).
Another study investigated the effects of free leucine supplementation (3g per day after training). It found the supplementation does not increase muscle strength or the cross-sectional area during resistance training in untrained young adults who consume an adequate amount of protein in their diets (12).
This study suggests you can achieve the best results by following a balance diet (hitting all the dietary references intakes) and supplementing it with BCAAs and protein shakes to elevate protein levels (12).
In a study the essential amino acids were found to increase muscle protein synthesis to a greater degree than other supplements. This highlights the importance of consuming all the essential amino acids not just the BCAA's to maximise the stimulation of protein synthesis (13). This need for all the essential amino acids is further credited by a study on amino acids and protein synthesis which found BCAAs alone are unlikely to increase protein muscle synthesis (14).
Regarding your diet, many foods contain high levels of BCAAs which can provide more than enough supplementation for you if you’re consistent and pay close attention to what you eat. Here’s a look at some of the best food sources for BCAAs:
3.5 ounces (100 grams)
1/2 cup (50 grams)
1 cup (235 ml)
1/2 cup (140 grams)
One of the big questions when it comes to BCAA supplements surrounds the issue of dosage. How much branched chain amino acid supplementation is recommended, and is there a right time to take them?
A study on BCAA supplementation and effective nutrition strategies found a dosage of between four and 20 grams (at least three BCAA capsules) per day is advised for optimal results including combating muscle protein breakdown (15). It also found that using supplements for longer periods while carrying out a strict training plan will increase athletic performance.
An intake of more than 200mg for each kilogram of body weight per day taken over ten days was found to be the most effective way to reduce EIMD, particularly when consumed before your workout.
While the earlier study shows that exercise-induced muscle damage effects are minimised when the dosage is taken before your workout, other studies have not demonstrated the correct timing for consuming BCAAs. There simply isn’t enough academic literature out there that has produced clear results (16).
BCAAs are an effective performance-enhancing supplement. Leucine, isoleucine, and valine can reduce muscle fatigue, combat muscle protein breakdown, promote protein synthesis, reduce recovery periods and enhance cognitive functionality. When taken in conjunction with a protein-rich diet or protein shakes, the effects of your BCAA supplements and leucine, in particular, are maximised, leading to increased protein synthesis, delayed release of serotonin, and reduced DOMS and EIMD. A dosage of 20g or three BCAA capsules is sufficient to achieve optimal results, but studies into the correct timing of dosages have, thus far, been inconclusive.