Shaun Ward MSc ANutr
Muscle protein is comprised of 20 different amino acids. 9 of these amino acids are labeled essential amino acids, meaning they cannot be synthesized in the body from other substances and are necessary to consume through the diet.
Further to this, 3 of the essential amino acids are named branched-chain amino acids, commonly termed BCAA’s, which are leucine, valine and isoleucine.
“Branched-chain” refers to the slight difference in their chemical structure compared to other amino acids, as they possess a branched side chain on their molecular structure.
Metabolically, BCAA’s are mostly known for promoting protein synthesis (cell generation of new proteins) and stimulating anabolic signaling pathways (cell communication for growth).
Out of the 3 essential amino acid, leucine is by far the most well-researched and seems to have the most significant impact on these metabolic functions.
Leucine serves as a substrate for the synthesis of new muscle proteins, and is also crucial for signaling and initiating the rate-limiting step in the production of new muscle proteins.
In fact, leucine is even looked at as the regulator of muscle protein synthesis due to its huge impact on modulating the activity of mTOR pathways - central regulators of cell metabolism, growth, and proliferation.
In turn, although they have other uses, the overriding goal of consuming BCAA supplements is to maximize the anabolic state.
The Benefits of BCAA
Below we've listed all the potential benefits of BCAA based on credible scientific studies:
BCAA May Help Signal Muscle Growth
BCAA’s have repeatedly demonstrated to increase intracellular anabolic signaling, and activate the key processes involved in the initiation of protein synthesis .
In general, an increase in the signaling for cells to generate new muscle protein usually leads to an increase in muscle mass, provided there are sufficient ‘building blocks’ for these proteins to be produced.
Specifically, there needs to be an adequate quantity of all the essential amino acids to build new muscle tissue.
When all the essential amino acids are available, this increase in anabolic signaling essentially works to accelerate the process of muscle protein synthesis - although it is not a necessity.
Due to this, BCAA’s may enhance the anabolic effect of a protein meal, especially when the given meal may not contain enough leucine to maximally signal anabolic processes. For example, the addition of 5 grams of BCAA’s to an insufficient amount of whey protein (6.25 grams) can increase muscle protein synthesis to the same level as seen with 25 grams of whey protein alone .
Thus, supplementing BCAA’s can induce a greater potential for an anabolic response of a protein-containing meal by activating the initiation factors for muscle growth.
BCAA May Improve Endurance Performance
BCAA’s taken during endurance exercise may help to prolong the onset of fatigue by reducing the accumulation of serotonin - a central fatigue substance .
It is also theorized that BCAA’s can act as an alternative fuel source during endurance exercise which may attenuate the rate of glycogen use - the bodies primary source of energy . As fatigue is so closely linked to muscle glycogen depletion in the later stages of endurance exercise, BCAA’s may help to prolong the time it takes to reach the point of exhaustion.
More research is needed in this area for a better analysis.
BCAA May Reduce Muscle Damage From Exercise
Consuming BCAA’s pre-exercise has shown to lower the increase in creatine kinase and lactate dehydrogenase, which typically reflect the degree of muscle damage from an exercise bout .
The positive effects of BCAA’s supplementation have been mainly reported for low-to-moderate muscle damage induced by exercise, whereas no significant benefit is seen for recovering highly damaged muscle tissue .
This effect is also thought to stem from BCAA’s ability to lower serotonin production during exercise.
However, more recent evidence has proposed that it may reduce markers of muscle damage by helping to scavenge reactive oxygen species during exercise - chemically reactive species that damage cells.
It should be noted that reducing muscle damage is not always necessarily positive, especially for athletes during training phases, as many adaptations to training are as a result of increases in the products of muscle damage.
BCAA May Promote Longevity
It has been demonstrated in animal models that long-term dietary supplementation with a BCAA-enriched amino acid mixture increases the average lifespan . How well this translates to human longevity is yet to be determined.
The mechanistic reasons for this could potentially be tied to the supposedly heightened reactive oxygen species defense system, speculated to reduce muscle damage during exercise, which may also lead to reduced oxidative damage in cardiac muscles.
The only other viable explanation for increased longevity would be due to upregulating mitochondrial biogenesis – the process of increasing the number of functional mitochondria.
Do BCAAs Actually Cause Muscle Growth By Themselves?
One of the main reasons why athletes and gym enthusiasts consume BCAA’s is in hope that they will facilitate their muscle growth.
However, far more studies actually find a net increase in muscle protein breakdown as opposed to a net increase in muscle protein synthesis when BCAA’s are consumed – at least when they are taken in isolation.
This is because BCAA supplementation alone will only cause a transient increase in muscle protein synthesis before becoming quickly limited by the availability of the remaining 6 essential amino acids which are all required to synthesize new muscle proteins .
For this reason, the stimulation of protein synthesis from BCAA’s alone cannot be sustained and will therefore not have a physiologically significant effect on muscle growth.
To worsen matters, as BCAA’s signal for muscle protein synthesis to occur, but are void of the other 6 essential amino acids, the body will release the other essential amino acids stored from within muscle tissue – causing muscle protein breakdown. In other words, when BCAA’s are taken alone, muscle protein breakdown is required to sustain muscle protein synthesis. Clearly, this is extremely counterproductive.
Not only this but it is estimated that BCAA use alone causes 30% more muscle protein breakdown compared to synthesis, resulting in a net loss of muscle tissue .
Therefore, foods or supplements which contain a good amount of the other essential amino acids are necessary to consume alongside BCAA supplementation for there to be a beneficial effect on muscle growth.
As stated earlier, BCAA supplementation can increase the anabolic response of a protein-containing meal if it does not already contain an adequate amount of BCAA’s to maximize anabolic signaling, but supplementation use for muscle growth outside of this scenario is negligible.
A Great Supplement for Vegans?
Although vegans are able to consume a protein sufficient diet, the slightly inferior amino acid compositions of plant-based foods mean that these foods will not create the same anabolic response compared to animal-based products.
Current advice for vegans is to increase the normal protein recommendations for athletes by ~10% to compensate for this reduced anabolic response .
However, another viable option to induce the same effect is for vegans to consume a serving of BCAA’s with each meal that may not contain a significant amount of protein (<25 grams).
For reasons already mentioned, this will increase the signaling of the protein contained within each meal to help maximize the potential for generating new muscle proteins.
How To Use BCAA
The best way to consume BCAA’s is yet to be found. One thing that we can say with certainty is that if an individual has a goal to increase muscle mass, it is best not to consume BCAA’s without other protein-containing foods.
If muscle growth is the goal, the best way to consume BCAA’s is to consume ~2-4 grams with each meal that does not contain at least ~25-30 grams of protein . If athletes already consume adequate amounts of protein in each meal, there is no need for additional BCAA supplementation.
For endurance athletes, it is advised to take 2-5 grams of BCAA's per hour of exercise.
To consume BCAA’s, either mix BCAA powder in with the recommended amount of water, or alternatively, a tablet-based BCAA supplement can be purchased. No current evidence suggests one form of consumption is superior to another.
BCAA Safety and Side Effect Information
BCAA’s have the potential to cause stomach problems in susceptible people such as nausea, vomiting, diarrhea, and bloating. In very rare cases, BCAA’s may cause high blood pressure, headaches, or skin whitening.
BCAA supplements are not recommended for those suffering from amyotrophic lateral sclerosis , or for individuals with a congenital disorder called maple syrup urine disease which causes issues with processing BCAA’s .
BCAA’s are 3 of 9 essential amino acids which humans need to consume from the diet.
Supplementing with BCAA’s is mainly used to increase anabolic signaling but may also have benefits such as improving endurance performance, reducing muscle damage from exercise, and even promoting longevity.
However, BCAA use alone has limited benefits as the other essential amino acids are required in adequate amounts to sustain the increase in synthesizing new muscle proteins. In fact, consumption of only BCAA’s may even cause a net increase in muscle protein breakdown.
The main use of BCAA supplementation should be to increase the anabolic response to a meal, especially when the meal contains an inadequate amount of protein to stimulate maximum anabolic responses by itself. The may be especially important for those following a vegan diet.