Andrew Reynolds and David Appleby

After hitting the gym, playing sports, or even going for a run, many athletes turn to protein and amino acid (AA) supplements to enhance muscle recovery and growth. Multiple studies suggest that individuals who regularly exercise or partake in high intensity training require more dietary protein and AAs than sedentary individuals. This additional protein not only allows the human body to repair itself, but is also required for everyday metabolic activities and immune function. Of the twenty amino acids that comprise muscle protein, nine are considered essential amino acids. These essential AAs are not able to be produced by the body on its own, and therefore must be ingested through one’s diet. While it is possible to obtain the necessary protein and nutrients through a regular balanced diet, evidence shows that supplementation before and after exercise may prove advantageous. Among the most popular and cost efficient are powdered proteins, found most commonly in the form of whey and casein. Whey protein, often referred to as “fast” protein, has been shown to elicit a sudden, rapid increase of plasma amino acids following ingestion, providing immediate delivery to the body. Casein, however, is known as “slow” protein and induces a rather progressive and prolonged increase in plasma amino acids. While the digestion of these different proteins has been found to mediate protein metabolism and synthesis after exercise, it is debated whether the use of branched-chain amino acids (BCAAs) augments these processes on its own.

The branched-chain amino acids make up approximately one third of skeletal muscle protein in the body, and account for three of the nine essential AAs. Of the three BCAAs are leucine, isoleucine, and valine, which have laid the foundation for a multi-million dollar industry of nutritional supplements. Distributors of BCAA supplements rave of their anabolic capabilities and claim of their role in muscle recovery when taken post-exercise, particularly in regard to leucine. Leucine has been said to not only act as a precursor for muscle protein synthesis, but also a regulator of intracellular signaling pathways involved in the process of protein synthesis. A few studies have reported that the ingestion of BCAAs increases protein balance either by decreasing the rate of breakdown, increasing the rate of synthesis, or a combination of both. Additionally, it was observed that pairing leucine supplements with carbohydrates and protein before and after workouts led to a heightened level of protein synthesis in the body when compared to trials where leucine was not present. However, the credibility and repeatability of the research behind these claims is unclear, and has been rebutted by other scientific studies.

In this study assessing BCAAs and muscle protein synthesis in humans, the idea that BCAAs alone are capable of promoting muscle anabolism is questioned. This claim has been put forward for more than 35 years, but has been chiefly recorded in rat and other animal studies, with almost no studies being conducted regarding the response to oral consumption. The study involves a detailed literature search, and evaluates the theoretical and empirical data used to make these initial claims regarding BCAAs. It discusses how skeletal muscle in humans comprises a much larger portion of total body mass than in rats and therefore leads to several differences in the way muscle protein synthesis is regulated. Another problem with these previous studies is that they often use the “flooding dose” technique, which involves the administration of an amino acid tracer over a very short time period, therefore neglecting any possibility of sustained effects. With that being said, many of the results found in past experiments employ methods that make the extrapolation of the data to humans unfitting and reduce the physiological significance. In addition, this study displayed how only two studies were conducted analyzing the intravenous effects of BCAAs in humans, noting in both that BCAAs decreased both muscle protein synthesis and protein breakdown. However, the rate of the catabolic processes that broke down muscle protein exceeded the rate of protein synthesis in both cases during BCAA infusion. Due to these findings, the researchers refuted the claim that consumption of dietary BCAAs initiates anabolic activity and increases muscle protein synthesis.

Overall, it is evident that additional attention to diet and supplementation is essential for athletes and individuals who regularly exercise in order to promote the growth and repair of muscles, and to maintain a healthy body. While use of protein powders in the role of muscle protein synthesis has been backed by extensive scientific research, it is still unclear of the extent to which BCAAs are capable of carrying out these same processes on their own. More studies need to be conducted in human subjects observing the activity and metabolism of proteins when dietary BCAAs are ingested to better determine the effectiveness of their use. Many factors come into play when assessing the best supplements to take in regards to exercise, including intake quantity, timing of ingestion, and interaction effects. After observing the conflicting research claims, the use of BCAAs alone may not yield noticeable results, but seems to have little to no risk involved in taking them. Many trainers and workout regimens advise the combination of protein supplements and BCAAs to maximize benefits, but the scientific research is still lacking.

Questions to Consider

1. What would happen if an individual took more protein supplements/BCAAs than the body needed?
2. How could studies be better designed to assess the role of BCAAs in humans?

Further Suggested Reading

[1] https://www.ncbi.nlm.nih.gov/pubmed/20048505

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5568273/

[3] https://www.ncbi.nlm.nih.gov/pubmed/16365096/

[4] https://jissn.biomedcentral.com/articles/10.1186/1550-2783-4-8

[5] http://healthyeating.sfgate.com/primary-role-protein-diet-3403.html