The Justice League is composed of a bunch of jacked up super heroes each with special powers put together to fight crime and maintain order.  Each member of the Justice League plays his role but the league is centered around one superhero, Superman.  The Amino Acids are just like the Justice League they are there to build muscle and fight the bad guys (cortisol, myostatin, muscle atrophy, ect).  If there is one amino acid that stands out and is more powerful than any other amino, Leucine is the Superman of the Amino Acids.  Several studies published this month documents leucine has both the ability to increase muscle growth and lose bodyfat.  Obviously, all Amino Acids are required to make proteins, but remarkably a large dose of leucine alone can stimulate human muscle protein synthesis1.  In fact, it has been reported that muscle protein synthesis responds linearly to plasma concentration of leucine14.  In other words, the more leucine you consume, the greater the muscle protein synthesis rates.  In this months Journal of Molecular Reproduction and Development, leucine does a whole lot more than just stimulating protein synthesis, it activates satellite cell activity. When muscles undergo intense exercise, as from a resistance training bout, there is trauma to the muscle fibers. This disruption to fibers activates satellite cells, which are activated to the injury site. In essence, a biological effort to repair or replace damaged muscle fibers begins with the satellite cells fusing together and to the muscles fibers, often leading to increases in muscle fiber hypertrophy. It has previously been documented that resistance exercise stimulates satellite cell activity; it is also well documented that insulin-like growth factor-1 (IGF-1) stimulates satellite cell activity. Leucine has some similarities to IGF-1 as both IGF-1 and leucine increase muscle size by stimulating mTOR signaling in skeletal muscle.  Researchers examined the effects of adding either leucine or IGF-1 to muscle satellite cells and found that both IGF-1 and leucine upregulated mTOR signaling in satellite cells8. In addition, there was no difference between IGF-1 and leucine for increasing satellite cell activation.  Activation of mTOR signaling is necessary for the protein synthesis in satellite cells stimulated by IGF-1 and leucine. This study was performed with muscle cell in test tubes but it makes you wonder could large dosages of leucine be just as effective as IGF-1 for stimulating muscle growth?  Adding a few scoops of leucine powder to your protein/carbohydrate beverage may increase the anabolic drive in muscle.  The coingestion of leucine (1 gram per kg of bodyweight) and protein with carbohydrate has been found to increased whole body protein synthesis compared with a combined ingestion of carbohydrate and protein. Interestingly, the combined ingestion of leucine and protein with carbohydrate may enhance IGF-1 levels as the insulin response of leucine, protein, and carbohydrates rose by ~250% compared with the ingestion of only carbohydrate25.  Adding some leucine to your post exercise drink may be the missing ingredient to enhance muscle growth.

Leucine: A Fat Loss Agent?
You have heard of myostatin knockouts mice, well get ready for the new genetically altered super leucine mouse.  Scientists disrupted the branched chain aminotransferase gene, which is the enzyme which breaks down BCAA in muscle.  In essence, the mice have genetically elevated levels of leucine. So is there anything unusual about these super leucine mice?  What interesting is that these mice exhibit elevated plasma BCAA’s but also decreased adiposity, despite eating more food, along with increased energy expenditure, remarkable improvements in glucose and insulin tolerance, and protection from diet-induced obesity12.  High dosages of leucine may be the able to prevent excess fat gain in the offseason when calories are high.  Another article of interest was published in the journal of Diabetes in which they fed rats a high fat diet but also doubled their leucine intake by adding it to their drinking water.   Even though the rats ate the exact same calories on the high fat diet increasing leucine intake resulted in up to 32% reduction of weight gain and a 25% decrease in adiposity. The reduction of adiposity resulted from increased resting energy expenditure associated with increased expression of uncoupling protein 3 in brown and white adipose tissues and in skeletal muscle10. Consider being like a rat for a while during the weeks leading up to the competition and adding leucine to your water supply.  The final article of interest was published in Journal of Life Sciences which they took rats and put on leucine and phenylalanine and then put them on a calorie restricted diet by 50% for 1 week.  The scientists then let the rats eat whatever they wanted for 2 weeks after that.  Compared to the group of rats that received nothing, chronic supplementation with leucine and phenylalanine was able to improve the body composition by increasing lean body mass and by reducing, although modestly, the accumulation of body fat11.  This means that bodybuilders may be able to prevent putting on excess bodyfat after dieting for a competition by taking leucine.  So based on these studies, bodybuilders should be taking leucine especially during the competition phase to reduce bodyfat but also stimulate protein synthesis rates.  I even suggest adding it to your drinking water like the lab rats!!!