BCAAs and Protein Synthesis
All muscle is made up of protein, and more specifically, amino acids. When you eat protein, it’s broken down into amino acids, which are then sent to tissues all around the body. There, they are reassembled into new proteins: muscle tissue. The body is constantly breaking down old muscle tissue (protein degradation) and building up new tissue (protein synthesis).
An anabolic state happens when protein synthesis is greater than protein degradation. When this happens, you gain muscle and enhance performance. There are a few ways of increasing protein synthesis; BCAAs have long been thought to do this. If true, BCAAs would be an invaluable supplement in gaining lean mass.
How do BCAAs Increase Muscle Protein Synthesis
Ingesting essential amino acids following strength training has been shown to increase protein synthesis in numerous studies. Other research says this can also be accomplished through the use of the BCAAs. Leucine alone is also thought to have a special role in increasing protein synthesis1.
The manner in which BCAAs increase protein synthesis is not entirely understood; here’s what we know. Leucine acts as the substrate or foundation for the creation of new muscle tissue and initiates the first step of protein synthesis. There are also various signaling proteins which begin and increase synthesis. BCAAs stimulate these signaling proteins. Some studies suggest leucine alone has this effect1 while others show the absence of valine and isoleucine reduces the effects of leucine on protein synthesis2.
BCAAs, and perhaps leucine on its own, may also have a role in decreasing protein degradation. Put together, these two actions increase muscle mass and enhance performance in a wide variety of activities.
What does the research say about BCAAs promoting protein synthesis?
Study 1: Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?3
This article looked into 13 studies examining the effects of BCAAs on protein synthesis. Because protein synthesis relies on the availability of all of the essential amino acids rather than only three, any increase in synthesis attributed to BCAA intake is quickly limited by the unavailability of the other essential amino acids. The body cannot build tissue from BCAAs alone. Authors stated, “dietary BCAA supplements alone do not promote muscle anabolism.” They concluded BCAAs alone cannot increase protein synthesis.
Study 2: A high proportion of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly4
This study looked at the effects of leucine on protein synthesis in both elderly and young subjects. Subjects were split into two groups. One group received whey protein (26% leucine) while the other group received a protein higher in leucine content (41% leucine). Researchers measured protein synthesis using various markers taken from blood samples and muscle biopsies.
Researchers concluded that higher leucine content has an important role in increasing protein synthesis in elderly individuals. Elderly subjects saw increased protein synthesis with the 41% leucine supplement. The younger subjects did not see this increase. The authors state that essential amino acids (rather than leucine alone) are a more important factor in increasing protein synthesis. They concluded that leucine may have a role in preserving muscle mass in the elderly population.
Study 3: Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men5
These researchers looked at the effects of leucine and essential amino acids on protein synthesis following a low dose of whey protein. They wanted to know whether certain amino acids compensated for a smaller dose of protein after strength training.
Researchers made a few conclusions. They found that a dose (0.75 grams) of leucine plus 6 grams of whey protein was as effective as a 25 gram serving of whey protein alone in increasing protein synthesis for a period of 1-3 hours following exercise. Still, a 25 gram serving of whey protein was able to sustain protein synthesis for a longer post-exercise period (3-5 hours) than leucine.
The authors stated that this longer sustainment of protein synthesis made a 25 gram dose of whey protein a better choice. These findings show that for those who are unable to tolerate a large post workout meal, smaller doses of whey protein combined with leucine can have similar anabolic effects.
The Bottom Line – Do BCAAs increase protein synthesis?
The first article looked at 14 studies and did not find any evidence to backup the claim. The second study found a very limited population in which leucine increased protein synthesis. The final study showed that leucine could stimulate protein synthesis, however a standard serving of whey protein did a better job.
At this time, the research does not support the claim that BCAAs increase protein synthesis for the vast majority of individuals. There is evidence that certain population groups or those who are unable to tolerate large meals may benefit from BCAA supplementation. However, when all of the essential amino acids are included in a meal, BCAAs do not seem to provide any further increase to protein synthesis.
References
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Jackman, S. R., & Witard, O. C. (2017). Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans. Frontiers in Physiology,8. doi:10.3389/fphys.2017.00390
- Zheng, L., & Wei, H. (2017). Effects of Supplementation of Branched-Chain Amino Acids to Reduced-Protein Diet on Skeletal Muscle Protein Synthesis and Degradation in the Fed and Fasted States in a Piglet Model. Nutrients,9(1), 17. doi:10.3390/nu9010017
- Wolfe, R. R. (2017). Branched-chain amino acids and muscle protein synthesis in humans: Myth or reality? Journal of the International Society of Sports Nutrition,14(1). doi:10.1186/s12970-017-0184-9
- Katsanos, C. S., & Kobayashi, H. (2006). A high proportion of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly. American Journal of Physiology-Endocrinology and Metabolism,291(2). doi:10.1152/ajpendo.00488.2005
- Churchward-Venne, T. A., & Burd, N. A. (2012). Supplementation of a suboptimal protein dose with leucine or essential amino acids: Effects on myofibrillar protein synthesis at rest and following resistance exercise in men. The Journal of Physiology,590(11), 2751-2765. doi:10.1113/jphysiol.2012.228833