If you search for “essential amino acids” on Google you will see many sites advertising branched-chain amino acids (BCAAs), and others advertising essential amino acids (EAAs). You may be left wondering: Are BCAAs and EAAs the same thing? If not, what’s the difference? Which is right for you?
The term branched-chain amino acids refers to the chemical structures of the amino acids leucine, isoleucine, and valine. These BCAAs are all essential amino acids, meaning they cannot be produced in the body and you have to get them via your diet or supplementation.
Of the three BCAAs, leucine, in particular, has been proposed to have a variety of regulatory roles in the body. Initial interest in the unique qualities of leucine concerned its primary role in stimulating muscle protein synthesis, or the building of new muscle tissue. We can trace this interest back to a 1975 study published in the Journal of Clinical Investigation that demonstrated leucine’s capacity to stimulate protein synthesis in isolated rat muscle.
The possibility that the same effect could be elicited in an intact organism was suggested by researchers Garlick and Grant, who showed in rats that a mixture of BCAAs increased the muscle protein synthesis response to insulin.
An important advance in the understanding of the potential mechanism by which leucine may play a role as a stimulator of muscle protein synthesis was made by Anthony et al. in a study published in the Journal of Nutrition in 2000. Investigators showed that leucine ingestion stimulated muscle protein synthesis in rats and that the increase in synthesis was accompanied by the activation of several molecular factors within the muscle cell that are required for initiation of the process of protein synthesis. These factors can collectively be referred to as the “initiation factors,” and the entire molecular processes involved in the initiation of protein synthesis can be referred to as “anabolic signaling.” Leucine, therefore, can activate anabolic signaling.
But an interesting phenomenon occurred when humans entered the research picture. When the study of leucine was extended to human subjects, it became evident that providing leucine alone disrupted the balance of plasma amino acids. Most notably, increased availability of leucine not only caused increased oxidation of leucine but the accelerated oxidation of the other branched-chain amino acids as well. Consequently, providing leucine alone was found to induce deficiencies in isoleucine and valine. As a result, all of the BCAAs are conventionally given as a nutritional supplement, although no special qualities of either valine or isoleucine have been identified.
So here’s what we know so far: Studies show that taking 2-4 grams of leucine as part of a complete BCAA dietary supplement may have beneficial effects on a variety of physiological endpoints, including recovery from exercise and mood and cognitive performance during prolonged exercise. There is no doubt that leucine can be considered a “nutraceutical,” a designation that honors its regulatory effects beyond its role as one of the building blocks of body proteins. Beneficial effects can be achieved by increasing the amount of leucine you consume each day.
Essential Amino Acids (EAAs) Explained
EAAs refer to the amino acids that are required in the diet because we cannot do without them and they cannot be produced in the body. As we’ve seen, the three branched-chain amino acids are categorized as essential amino acids, along with six other amino acids.
EAAs play a variety of important roles in the body, including acting as precursors for the production of brain neurotransmitters and supporting immune function. However, the main role of EAAs is as constituents of proteins, including muscle protein.
Since all proteins in the body are continually broken down and resynthesized, an adequate supply of all the EAAs is required or body protein will be lost. Most of the EAAs in body protein that are released as a result of protein breakdown is available for reincorporation into protein. However, approximately 15% of the EAAs released from protein breakdown are oxidized, which means they are irreversibly lost. The EAAs that are oxidized must be replaced through your diet since they cannot be produced in the body.
There are 9 essential amino acids:
Every single one of these is required to make muscle protein.
Muscle Protein Synthesis
The rate of muscle protein synthesis is determined by the availability of EAAs. If there are not enough EAAs, then muscle protein synthesis is limited. Following a meal containing protein, or ingestion of an EAA supplement containing all the EAAs, muscle protein synthesis is stimulated. The stimulation of muscle protein synthesis by EAAs is dose-dependent. The more EAAs ingested (up to 15 grams) the more potential for muscle building. Conversely, if levels of EAAs in the blood are reduced, then the rate of muscle protein synthesis is reduced correspondingly. You can learn more about this process in my book: A Guide to Amino Acid and Protein Nutrition: Essential Amino Acids for Everyone.
The most important takeaway is that all the EAAs are required to make new protein. This can best be understood by thinking about how proteins are made. Each protein in the body is a long string of amino acids linked together in a specific order. Protein is produced by hooking together amino acids one by one in the order dictated by messenger RNA in the cell. If a point is reached where the next amino acid due to be incorporated into the chain is not there, production of the protein will stop.
Where Do the Amino Acids for Protein Synthesis Come From?
Amino acids released from protein breakdown are the main source of amino acids for the synthesis of new proteins in the basal state. (The basal state is the resting metabolic state of the body in the morning after 12 hours of fasting.) On average, about 85% of amino acids from protein breakdown are re-used for protein synthesis. In order to increase the rate of protein synthesis to greater than the basal rate, the efficiency of reutilization of the amino acids from protein breakdown must be increased, and/or the availability of EAAs must be increased by additional consumption.
The bottom line is that all the EAAs must be available for muscle protein synthesis, and consumption is the primary source.
BCAAs and Muscle Protein Synthesis
What we’ve learned thus far is that leucine, valine, and isoleucine are all EAAs that are components of muscle protein. In addition, leucine can increase the efficiency of protein synthesis by activating the initiation factors. All the BCAAs are therefore important in the stimulation of the synthesis of new muscle protein.
However, if only BCAAs are consumed they are limited in their ability to stimulate muscle protein synthesis. That’s because all the EAAs are required for a complete protein to be produced, and in the basal state, the only source of EAAs is from protein breakdown. Since most of those EAAs are already reincorporated, the maximal increase in protein synthesis is limited by the availability of the other EAAs. For this reason, BCAAs alone have been found to have either no effect or a minor effect on the rate of muscle protein synthesis in human subjects.
BCAA or EAA Supplements—Which Are Better?
There is no question that BCAAs are important for many functions in the body, including protein synthesis. However, the full benefit of BCAAs cannot be achieved if they are taken by themselves, because you cannot make a complete protein out of just three amino acids. The maximal effectiveness of the BCAAs is only achieved when they are taken along with the other six EAAs. Only a mixture of all the EAAs can provide a sustained stimulation of muscle protein synthesis. The nonessential amino acids in protein can be made in the body and are therefore not required in a dietary supplement.
A non-scientific analogy might be helpful in understanding the difference between BCAAs and EAAs. Think of EAAs like different players on a football team. In this analogy, leucine is the quarterback that calls the signals and is the most important player on the team—what team wins without a good quarterback? However, a team of just quarterbacks wouldn’t be very successful, and neither is an amino acid supplement made up entirely of grams of leucine.
All the positions on the team have an essential role to play, and without enough players for each position, the team will fail. Similarly, all the EAAs are required for the effects of leucine to translate to increased production of muscle protein. Consumption of a dietary supplement containing a balanced mixture of all the EAAs that includes a generous proportion of leucine is necessary for maximal results.