If you’ve spent any time in a weight room lately, you’ve probably been asked if you’re taking branch-chain amino acid supplements—sometimes referred to as “BCAAs.” There is no hotter supplement right now among body builders or recreational athletes looking to maximize their strength gains. But is there science to back up the BCAA hype? Yes and no. Let's start with the basics.
What are amino acids?
Amino acids are the building blocks of proteins, which are the macromolecules that make up muscle. In order for your body to make protein, it requires 20 different amino acids—nine of which it has to get from the stuff you eat. These nine are known as “essential amino acids” because your body can’t make them and you can’t live without them, says Robert Wolfe, a professor at the Reynolds Institute on Aging at the University of Arkansas for Medical Sciences.
Wolfe has conducted three decades of NIH-funded research on muscle metabolism. He explains that the protein in your muscles is in a continual state of being broken down and reproduced. “In order to make protein—or muscle—all 20 of these essential amino acids have to be available to the body in adequate amount,” he says.
So what are branch-chain amino acids?
Among those nine essential amino acids, three are termed “branch-chain” amino acids because of their specific chemical structure. These three are leucine, isoleucine, and valine, and there’s evidence they play an outsize role in promoting muscle growth.
One 2006 study in the Journal of Nutrition found BCAAs can “activate key enzymes” that promote muscle growth. More research shows taking BCAA supplements can also help a person hold onto muscle mass even while eating a low-calorie diet.
One of these BCAAs in particular, leucine, seems to stand above the rest when it comes to kick-starting muscle growth. “Leucine can be looked at as the quarterback,” Wolfe says. “You need all nine players to form a team”—meaning you need all nine essential amino acids to produce muscle—"but leucine is the key.”
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Should I be taking BCAA supplements?
No. You should be taking supplements that contain all nine essential amino acids—albeit with an extra helping of leucine.
“The concept of taking BCAA supplements is that muscle protein synthesis is limited by biochemical processes, and that these supplements will initiate that process,” Wolfe says. “But that concept ignores the basic problem that you can’t make something out of nothing.”
He says taking BCAAs without the other six essential amino acids is unhelpful—like trying to start a grill with lighter fluid but no charcoal. “I’ve looked at this for many years, and there are really no beneficial effects in terms of muscle growth if you’re taking BCAAs alone,” he says.
There’s a growing body of research to back him up on this. One recent study from the UK found BCAA supplements alone do not maximize muscle growth. All nine essential amino acids are needed, that study concluded. “Athletes interested in enhancing muscle growth with training should not rely on these BCAA supplements alone,” the authors of that study said in a press release.
Todd Astorino, a professor in the department of kinesiology at California State University San Marcos, reiterates some of Wolfe’s points. He says supplements containing all nine essential amino acids “clearly enhance protein synthesis.” The same can’t be said of pills or powders that contain only BCAAs.
How beneficial are essential amino acid (EAA) supplements, and what should I shop for?
Based on his research, Wolfe says these supplements are, on average, around three times more effective at promoting muscle growth than whey protein, which is the former gold standard for athletes looking to safely maximize muscle growth using OTC supplements.
Wolfe says there are several easy-to-find EAA supplements on the market today. And, now that the research is tilting the scales away from BCAAs and toward more-complete amino acid supplements, many more are poised to drop later this year.
While he isn’t willing to single-out specific products, Wolfe says athletes who want to maximize muscle gains should look for EAA supplements that contain 20 percent to 30 percent leucine (which, again, is the muscle-synthesis-stimulating QB of amino acids).
EAA supplements should also benefit older adults in danger of losing muscle due to aging, Wolfe says. But for this population, he says a supplement with a higher proportion of leucine—something around 40 percent—is a better fit.
He recommends ingesting EAA supplements before or during a workout, and says that these supplements are not a replacement for whey protein. “I think if you take them together, you get the benefits of both,” he says. “They don’t compete with each other.”
Are EAA supplements safe?
“Based on the research we have to date, there are no known adverse effects,” Wolfe says. “The thing to understand is, these are essential nutrients—you’re not giving something to the body that it isn’t used to seeing already.”
He says there have been some concerns that overdoing it with EAA supplements could put an extra burden on a person’s kidneys. (Protein digestion can create a byproduct called urea, which your kidneys have to deal with. And too much urea can lead to kidney stones or kidney damage.) But essential amino acids alone do not increase urea in the kidneys. “They can actually reduce the urea load on the kidneys,” he says.
While there is some research linking BCAAs to insulin resistance and diabetes, the long-term effects of taking amino acid supplements really aren’t known. “I don’t freak out about these supplements, especially if the person taking them is healthy, but I might urge caution if you’re at high risk for diabetes,” says Mark Moyad, director of preventive and alternative medicine at the University of Michigan, and author of The Supplement Handbook.
Also—and this holds for any supplement—be sure to look for a product that doesn’t contain a bunch of add-on ingredients. “Protein and amino acid supplements are a billion-dollar industry, so all these companies are trying to differentiate their products,” Moyad says. To do that, they often throw in extra ingredients—antioxidants or vitamins or plant compounds. “But when they start adding other things, they get away from the science of what works, and there are a lot of unknowns,” Moyad says.
Those caveats aside, if you’re in good shape and looking for a safe, effective way to maximize your workout gains, essential amino acid supplements look like one of your best options.
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