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Expressway to image1

Posted in: Articles by ProSource, Featured Content, Supplement Articles
By Chad Kerksick, PhD | Jul 25, 2012



Leucine, Essential Amino Acids
and the mTOR Muscle Growth Pathway


Expressway to image Do you know what nutrients are best consumed in combination with your regular workouts?  A great many people consume increased amounts of protein because they know when combined with a consistent heavy resistance training program it can help facilitate greater adaptations to their training.  These desired adaptations are often increased strength and lean muscle tissue as well as improvements in body composition.  Another topic commonly discussed of late has been nutrient timing.  Do you know when you should be consuming these nutrients?  A number of published scientific articles and recent articles on the ProSource website have addressed this topic and this is an area that many sports nutrition researchers are working hard to better understand.

How many of you know why you should consume these nutrients?  I'm not just talking about, "Because they increase muscle growth!"  How many of you know what factors have been shown in scientific studies to be influenced inside your body as a result of taking nutrients like protein? This article will outline the key aspects of muscle growth which are thought to actually occur insider your muscles' cells.

For starters, a number of factors must be in place to stimulate positive changes in muscle growth and body composition.  The overall power and influence of a consistent, sound resistance training program cannot be understated.  If you aren't regularly hitting the gym, using intensity levels that challenge your muscles and selecting exercises that use a large amount of muscle, positive improvements in muscle mass and body composition will likely be difficult to achieve.

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Muscle growth and amino acids
Other key factors include getting enough calories in your diet and getting optimal amounts of key amino acids.  Consuming the right amount of calories day in and day out is critical to help stimulate favorable body composition changes and a full discussion is beyond the purpose of this article.  Cutting calories too much even with an intense resistance training program can create too much of an energy shortage that leaves your body starving for nutrients to fuel all of the internal processes needed on a daily basis.  Overeating, on the other hand, supplies enough calories for muscle growth, but also results in fat growth; not the outcome you were hoping to achieve.

That leaves the intake of key proteins and amino acids which have been shown to stimulate increases in lean tissue, strength and other favorable adaptations.  The best protein sources for muscle growth and recovery provide the greatest amounts of the essential amino acids (Phillips 2009); those shown by research to be exclusively required for muscle growth (Tipton 1999; Volpi 2003).  For no other reason, this is why protein products which contain whey protein isolate such as ProSource's NytroWhey Ultra Elite are invaluable.  But why?

The mTOR pathway to anabolism
A number of components inside muscle cells have been discussed, but no other molecule has been discussed as much as mTOR, which stands for the mammalian target of rapamycin.  Scientists have identified mTOR as a central nexus for cellular growth. A better picture to get in your head is that of the hub of a wheel with a number of spokes coming from the hub.  The spokes represent the many different factors which can increase or decrease the activity of mTOR, which in the end will all go on to impact the extent to which the cell in question grows.  Remember in this case we are most concerned with the growth of muscle cells.  

Interestingly, a number of factors have been suggested to impact the activity of mTOR and these factors are commonly referred to as "upstream" factors.  Two "downstream" factors or those factors which are impacted as a direct result of mTOR activity, however, have dominated the scientific literature.  These two factors are called p70s6k and 4E-BP1.  Come again?  p70 what?  4E-BP who?  Did you just sneeze while typing on the keyboard?  I realize it seems like alphabet soup and candidly a definition of the letters and numbers isn't important.  Remember this!  The first factor, p70s6k, helps to increase the production of key molecules called ribosomes which are "make or break" molecules in the process of building new muscle proteins.  4E-BP1 is closely involved in the process called translation where a complex code of molecules is translated resulting in the building of proteins.  When activated by mTOR, 4E-BP1 helps to initiate or begin the translation process, which contributes to the growth of new proteins.  Certainly, a number of other factors can be discussed resulting in a growing array of arrows being drawn to and from mTOR, but that would be overkill.  In summary, high quality dietary proteins like whey, casein, egg and other animal proteins contain high amounts of the essential amino acids which research has shown to stimulate positive changes in mTOR which then goes on to positively impact two key factors, p70s6k and 4E-BP1, leading to increases in muscle protein growth.

For reasons scientists have yet to fully understand, the essential amino acid, leucine has been shown to play a critical role in the process of muscle growth.  For example, a number of very detailed and specific studies involving just muscle cells and laboratory animals continually suggest that the mere presence and the overall amount of leucine can impact the extent to which anabolic process in muscles are impacted (Garlick 2005).  For example, when sixteen healthy male subjects consumed either no drink or a leucine-enriched drink containing carbohydrates and other amino acids one hour after completing a bout of resistance training, rates of muscle protein synthesis were increased to a greater extent after the leucine containing drink.  Moreover, when the researchers specifically examined the expression of key proteins such as mTOR, p70s6k and 4E-BP1, all of these key molecules were expressed to a greater extent after consumption of the leucine containing drink (Dreyer 2008).  Additionally, a recent scientific review of articles devoted specifically to the impact of resistance exercise and nutrients (with particular emphasis on leucine-enriched solutions of the essential amino acids) was published (Drummond 2009).  In this review, the authors reported that both resistance exercise and nutrients alone or in combination can stimulate positive changes in muscle protein growth as well as the activity of mTOR and signaling to its downstream targets (e.g. p70s6k and 4E-BP1).  In highlighting the available research, the authors concluded that the mTOR communication pathway within muscle cells is a key and central pathway which controls rates of muscle protein growth.  Furthermore, the authors recommended that essential amino acid ingestion occur shortly following a bout of resistance exercise to promote muscle protein growth (Drummond 2009).

The importance of protein intake, and specifically leucine and essential amino acid intake, cannot be overstated.  In this respect, a recent study had eight healthy adults cycle for 60 minutes at 60% of their capacity and consume a drink which contained either 1.87 or 3.5 grams of leucine.  Regardless of leucine content, both drinks contained a total ten grams of the essential amino acids, which would be similar to around 20 grams of a whey protein isolate.  In recovery from the exercise bout, rates of muscle protein synthesis were higher when greater amounts of leucine were ingested (Pasiakos 2011).

In closing, optimal protein intake and specifically the intake of the essential amino acids and in particular leucine continue to be shown in research to be a critically important first step in promoting an environment inside your muscles where they can grow.  While various protein sources exist, whey protein isolates regularly contain the highest amounts of these important nutrients. Among whey products, it's hard to do better than the ProSource's own NytroWhey Ultra Elite, which contains an elite-quality, growth-factor-rich CFM whey isolate combined with a premium, ultra-rapid action super whey hydrolysate (WPH) and Leuvonâ„¢ 590, a highly bioavailable Leucine- Bound Leucine Peptide with a remarkable capacity to help switch on anabolism.  Certainly, NytroWhey Ultra Elite contains impressive amounts of the essential amino acids, including up to four times the leucine content of competing protein formulations.  

In this respect, regularly supplementing your diet with supplements like NytroWhey Ultra Elite within an hour after each workout can help you take advantage of not only key nutrient timing considerations but also the latest scientific research which shows that the combination of physical exercise and essential amino acid availability can maximize your body's ability to grow bigger and better muscles.


References
Dreyer, H. C., M. J. Drummond, et al. "Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle." American journal of physiology Endocrinology and metabolism (2008) 294(2): E392-400.

Drummond, M. J., H. C. Dreyer, et al. "Nutritional and contractile regulation of human skeletal muscle protein synthesis and mTORC1 signaling." J Appl Physiol (2009) 106(4): 1374-1384.
Garlick, P. J. "The role of leucine in the regulation of protein metabolism." J Nutr (2005) 135(6 Suppl): 1553S-1556S.

Pasiakos, S. M., H. L. McClung, et al. "Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis." The American journal of clinical nutrition (2011) 94(3): 809-818.

Phillips, S. M., J. E. Tang, et al. "The role of milk- and soy-based protein in support of muscle protein synthesis and muscle protein accretion in young and elderly persons." Journal of the American College of Nutrition (2009) 28(4): 343-354.

Tipton, K. D., B. E. Gurkin, et al. "Nonessential amino acids are not necessary to stimulate net muscle protein synthesis in healthy volunteers." J Nutr Biochem (1999) 10(2): 89-95.

Volpi, E., H. Kobayashi, et al. "Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults." Am J Clin Nutr (2003) 78(2): 250-258.


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Disclaimer: The articles featured herein are for informational purposes only and should not be construed as medical advice. Specific medical advice should only be obtained from a licensed health care professional. No liability is assumed by ProSource for any information herein.





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