Leucine in Your Protein – What is it and Why Does it Matter?

I’m sure many of you have heard of Branched Chain Amino Acids, or BCAAs for short. These are the amino acids that people sip on during workouts to improve recovery and gain muscle. Leucine is the main BCAA; it’s the one that’s responsible for all of the muscle-building effects.

What makes leucine unique is that it’s not only a “building block” of muscles as most amino acids typically are. Rather, leucine acts as more of a signal in the body that new muscle protein should be built. It’s an anabolic trigger, if you will. But research shows that in order to activate this muscle-building trigger, you need to hit a threshold amount of leucine, roughly 3-5 grams depending on your bodyweight.

Why does any of this matter though? I mean, I drink my protein shakes and consume a lot of protein from whole foods. Does having more leucine really make that much of a difference?

The answer is yes. Studies in humans show that even in the presence of a high protein meal, adding leucine further augments protein synthesis [1]. Since protein synthesis is what creates new muscle tissue, it stands to reason that optimizing your leucine amount per meal, even if your meal is high in protein, may further boost muscle gain. In fact, recent studies suggest that the chief factor in determining how well a protein builds muscle is how much leucine the protein contains [2].

Now, 100% whey protein products are roughly 10% leucine by protein content, which means your average 20-25g scoop of protein only contains 2-2.5g of leucine, not enough to hit the threshold amount to activate the anabolic trigger. Translation: chances are your protein powder is short-changing you in the leucine department, especially if cheap forms of protein are being used to “bulk up” the total protein number. The solution? Add leucine to your diet. In Select Protein, you’ll find added PepForm™ Leucine peptides, which is one form of leucine we are big fans of. You can also take an amino acid supplement like Amino IV which contains 5g Leucine per serving.

By consuming extra leucine alongside the complete amino acid profile of a protein shake, you maximize all your bases for muscle gain: you provide both the building blocks and the anabolic trigger for creating new lean muscle.


  1. Rieu, I, et al. "Leucine Supplementation Improves Muscle Protein Synthesis in Elderly Men Independently of Hyperaminoacidaemia." The Journal of Physiology 575.1 (2006): 305-15. Print.
  2. Norton, L. E., G. J. Wilson, D. K. Layman, C. J. Moulton, and P. J. Garlick. "Leucine Content of Dietary Proteins Is a Determinant of Postprandial Skeletal Muscle Protein Synthesis in Adult Rats." Nutrition & Metabolism 9.1 (2012): 67. Web.
Leucine in Your Protein – What is it and Why Does it Matter?
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