These days, branched-chain amino acids (BCAAs) have become a popular beverage to sip during training. They're easy to digest, so they get to your muscles quickly, and they help minimize breakdown. And for people who don't like to drink plain water, they offer a more enticing, flavorful way to hydrate.

BCAAs are made up of three essential amino acids (EAAs): leucine, isoleucine, and valine. Of these three, leucine has been shown to have the most positive impact on muscle growth and repair. So BCAAs are obviously the choice to build muscle, right? Well, maybe not.

There's evidence to suggest that there's more to muscle protein synthesis (a measure of the extent to which muscle building is stimulated) than leucine-rich BCAAs. It may be that choosing a complete protein (a protein that contains all nine essential amino acids) is the better choice.

Understanding The Role Of Leucine

In a rat study published in The FASEB Journal, researchers observed elevated leucine levels in the blood well after muscle protein synthesis (MPS) had returned to baseline. If muscle building stops while there is still leucine in the blood, then there may be more to stimulating maximum MPS that leucine alone.

Creating optimum muscle protein synthesis is an energy-intensive process. And while leucine has been shown to optimize peak muscle building, it may not be so good at sustaining it. In other words, leucine is great at flipping the switch to "turn on" MPS. But if muscle building starts to fade shortly afterward, that's not an ideal solution, especially during longer workouts. After all, you want MPS to continue for as long as possible!

Choosing A Better Whey

Research in rats and human models has demonstrated that muscles can more efficiently utilize "intact" leucine (the kind found in whey protein) than free-form leucine (found in BCAA supplements). This suggests that whey may provide a superior MPS response than BCAAs.

In a similar study, elderly subjects were provided either an EAA supplement or whey protein supplement (with the same amount of EAAs). At the conclusion of the study, the whey protein group experienced a greater muscle-protein balance. But why?

Looking Beyond Leucine

Mike Roberts, PhD, and his team at Molecular and Applied Sciences Laboratory at the University of Auburn has been conducting preliminary research into the role other bioactive compounds in whey protein play in stimulating MPS. In particular, the researchers have been examining something called "whey-protein-derived exosomes."

Exosomes are nanoparticles in our blood, saliva, and other body fluids. Their role is to carry protein and other compounds throughout the body. Using a sophisticated methodology, Roberts' team found that these nanoparticles had a distinct, positive impact on muscle protein synthesis.

"When you consume whey protein, a 1-4-hour increase in muscle protein synthesis will result from the leucine content," says Roberts. "However, you may also experience a modest and continued elevation in protein synthesis thereafter due to whey-protein-derived exosomes stimulating this process in skeletal muscle."

Making The Smart Move

As of today, there's not enough definitive research to say that a complete, fast-acting protein such as whey is superior to a BCAA supplement. However, the research seems to be leaning in that direction. If you're looking to maximize muscle growth—or to maintain it during a fat-loss phase—the smart move would seem to be the "whey way."