New Study Looks at Branched-chain Amino Acids for Muscle Hypertrophy


New Study Looks at Branched-chain Amino Acids for Muscle Hypertrophy

There’s little doubt that you need protein for muscle growth. The purpose of resistance training is to create microscopic damage within muscle fibers, thereby forcing the muscles to repair. To repair, muscle fibers call on satellite cells located just outside the muscle fibers. When the fibers are damaged from the stress of training, the satellite cells fuse with muscle fibers and donate their own nuclei. These additional nuclei help the damaged muscle fiber build new, myofibrils, or contractile elements. As a result, the fiber increases in thickness. So, it’s the repair process that ultimately leads to muscle hypertrophy and the toned, defined muscles you see when you look in the mirror.

Of course, repair of damaged muscle fibers won’t be very effective if your muscle cells lack the building blocks for forming new muscle fibers – amino acids from protein. Also important for muscle hypertrophy are hormones and growth factors that turn on muscle protein synthesis. You’re probably familiar with some of these anabolic hormones and signaling molecules, including testosterone, growth hormone, and IGF-1, a growth factor that acts directly on muscles cells to enhance muscle hypertrophy. Insulin plays a role too, as it promotes uptake of amino acids into cells, so the muscle cells can use them for repair and growth.

Not all amino acids are created equal with regard to their impact on muscle tissue. A group of amino acids you’ve probably heard about are the branched-chain amino acids. The branched-chain amino acids are leucine, isoleucine, and valine, three amino acids that have a chemical structure that branches, much like the branches on a tree. The three branched-chain amino acids are essential, meaning that you must get them through diet since your body can’t make them. These amino acids are abundant in muscle tissue where they play a role in muscle growth. One of the branched-chain amino acids, leucine, is especially important for ramping up muscle protein synthesis.

What makes leucine so special? This essential amino acid plays a pivotal role in activating a pathway involved in muscle protein synthesis called the mTOR pathway. Leucine works together with insulin to jumpstart the synthesis of new muscle proteins, the kind you need to thicken muscle fibers. Not that the other branched-chain amino acids aren’t important, leucine is just the “head honcho” when it comes to turning on the synthesis of new muscle proteins. It acts as a sort of on switch to get the process started.

What New Research Shows About Branched-chain Amino Acids

Because branched-chain amino acids, particularly leucine, play such a vital role in turning on muscle protein synthesis, a growing number of bodybuilders take a branched-chain amino acid supplement, one containing leucine, isoleucine, and valine. That might sound like a good idea, but a new study suggests that this may not be the best approach for building muscle.

In a recent study, researchers at the University of Stirling found that taking branched-chain amino acids alone was less effective than taking the full repertoire of amino acids your body needs after a workout. Much like isolating a particular beneficial component doesn’t always give the same health benefits as the whole food does, taking isolated branched-chain amino acids supplements may not be optimal either. Based on this study, you’d be better served to take a whey protein supplement or simply getting protein from food sources rather than taking isolated amino acids. In the study, the branched-chain amino acid supplement boosted muscle protein synthesis more than a placebo but a whey protein supplement in an equivalent amount more than doubled the response. The amount the participants took was 20 grams.

Are There Other Benefits of Branched-Chain Amino Acids?

One of the most unpleasant aspects of weight training is delayed-onset muscle soreness, the achy muscles, and stiffness you experience when you first start training or increase the stress you place on your muscles. Ouch! The stiffness and soreness make it hard to get around and train and it can last for up to a week. Some studies show that branched-chain amino acids could help prevent the symptoms of delayed-onset muscle soreness. In one study, participants who took a branched-chain amino acid supplement prior to doing squats reported less post-workout soreness and muscle fatigue than those who didn’t.

Some studies also show that branched-chain amino acids reduce central fatigue. When you do demanding exercise, one of the factors that limit your performance is central fatigue. Central fatigue is your nervous system’s attempt to slow you down, usually before your muscles have completely fatigued. (peripheral fatigue) One of the causes of central fatigue is excess tryptophan in the brain. Consuming branched-chain amino acids suppresses the uptake of tryptophan into the brain, thereby reducing central fatigue.

Getting Enough Protein for Hypertrophy

As this new study suggests, taking isolated amino acids, even ones that directly activate key muscle-building pathways may not be as effective as simply getting enough dietary protein and regularly consuming protein and carbohydrates after a workout. Meat and dairy contain substantial quantities of leucine, and even if you don’t eat animal products, soybeans and pea protein are excellent sources of branched-chain amino acids, including leucine. Branched-chain amino acids have benefits but they seem to work best in conjunction with other amino acids. If you prefer a quick and easy source of protein, drinking a whey protein shake or pea protein shake should supply your muscles with the branched-chain amino acids they need.

If you use any type of protein powder or supplement, including whey, buy from a reputable manufacturer as independent testing has detected contaminants in some powdered protein supplements, including contamination with heavy metals. Imagine if you use a protein supplement every day that contains heavy metals!

The Bottom Line

Branched-chain amino acids are still important, especially leucine, as they signal the muscles to synthesize more muscle protein. However, you don’t need branched-chain amino acid supplements and this study suggests that taking one may not be as effective as using whey protein. Keep that in mind before investing in an expensive container of branched-chain amino acids.



Eurekalert.org. “Not All Muscle Building Supplements Are Equal”
J. Nutr. February 2006. vol. 136 no. 2 533S-537S
WebMD. “Branched-Chain Amino Acids”
J. Nutr. February 2006. vol. 136 no. 2 529S-532S.
J. Nutr. January 2006. vol. 136 no. 1 333S-336S.


Related Articles By Cathe:

Buyer’s Guide to Amino Acid Supplements

Branched-Chain Amino Acid Supplements: Why You Don’t Need Them

Will Eating Protein at Bedtime Help You Build Muscle?

Can You Consume Too Much Protein?

Why Leucine is Key for Muscle Growth

Branched-Chain Amino Acids: Can They Help You Get Fit Faster?


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