Leucine Triggers Muscle Growth Post Workout

by - 12:06 PM

From the first time athletes, bodybuilders, and fitness enthusiasts started slamming down chicken breasts, steak, raw eggs (I know...I've been there) the big question has been how much protein do we need.

But are we asking the right question or would the "how much?" be better followed up with "what kind?"

Let's begin with what we know about protein... 

  • Proteins form the basic machinery of all cells. 
  • Proteins are made of of amino acids. 
  • Each amino acid plays a different role in the body - nervous system function, blood sugar regulation, energy metabolism, and muscle muscle protein synthesis to name a few.
  • Many amino acids are essential- we cannot synthesize them, and therefore must ingest them as part of our diet. 
  • Since we have no way to store amino acids for later use, our bodies have a daily requirement for them. 
  • Therefore, we must ingest each amino acid, roughly in the proportion we require it, every day. 

Whether you’re interested in building muscle or preventing muscle loss that normally occurs during dieting and aging, stimulating protein synthesis is absolutely key. Most people know that consuming protein induces an increase in muscle protein synthesis, which is why protein supplements are popular to consume after exercise. Now researchers are refining their knowledge on why protein stimulates anabolism (building up) in muscle. Scientists have shown it is the level of amino acids in the blood that directly boosts protein synthesis in muscles. In particular, the amino acid leucine is most highly related to muscle protein synthesis.

Researchers recently examined muscle protein synthesis after feeding animals various formulations of amino acids and compared them to glucose ingestion. When a complete protein (one that contains all the amino acids) was consumed, protein synthesis increased. When just essential amino acids were consumed without non-essential amino acids, the same increase was noted indicating non-essential amino acids are not required to stimulate protein synthesis. When only BCAAs were consumed, there was again the same increase in protein synthesis. Finally when just leucine was consumed, protein synthesis still increased to the same magnitude. These findings provided strong evidence that leucine was the driving force behind the ability of dietary protein to stimulate protein synthesis.

The amount of leucine to take post workout is still a matter of debate, however most studies show a range of about 3.2 - 4.4 grams needed to reach the leucine threshold for muscle protein synthesis. This can be attained in one of two ways: eating higher amounts of proteins (chicken, beef, whey) to reach leucine needs or by supplementing with leucine itself. The following is a chart of protein sources needed to attain leucine threshold.

Bottom line...All protein sources aren't the same.  Whether 30% of your total caloric intake is protein or only 15%  make sure you are getting the most bang for your buck by reaching leucine threshold and maximizing muscle protein synthesis.

1. Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men J. Physiol. June 1, 2012 590:(11) 2751-2765
2. Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjectsAm. J. Physiol. Endocrinol. Metab. April 1, 2005 288:(4) E645-E653
3. Leucine triggers muscle growth. J. Volek. Retrieved from http://www.nutritionexpress.com/article+index/authors/jeff+s+volek+phd+rd/showarticle.aspx?articleid=807

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