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The Switch That Controls Lean Body Mass

Posted by Dr. Robert Portman on 9/5/2018
The Switch That Controls Lean Body Mass
Most of the muscle adaptations that increase strength and endurance occur in the interval following moderate to intense exercise. Central to these adaptations is the repair and rebuilding of muscle protein. Although your muscles have multiple mechanisms to activate muscle protein synthesis the central mechanism involves a protein called mTOR. mTOR is a critical cellular switch that activates the cellular machinery responsible for repairing and building new muscle mass.

Over the last decade researchers have defined the role nutrition plays in mTOR activation. As one would expect, consuming a protein beverage should turn on the mTOR switch and that is what studies have shown. The key amino acid in protein responsible for turning on mTOR is leucine, a branch chain amino acid. Other branch-chain amino acids such as valine and isoleucine have a more modest effect on mTOR activation. It’s logical to ask, why not just consume a protein beverage after a workout for maximum recovery?

Many people do and there are a number of problems with this regimen. One, after a hard workout, muscle energy stores, particularly glycogen, are depleted. If these are not replenished, recovery is negatively impacted. That’s why carbohydrate is an essential part of any recovery drink. Two, protein slows gastric emptying. Since recovery nutrition should be consumed with a 30-45 minute window after exercise for optimum effect a protein drink slows absorption and nutrition may not be available while the recovery window is open. The result- a less complete recovery. However one of the important reasons is that carbohydrate has a major impact on mTOR activation. When carbohydrate is consumed, insulin is released. Although we think of insulin as primarily involved in carbohydrate metabolism, insulin plays a major role in turning on protein synthesis and activates mTOR. Because insulin plays a central role in protein synthesis as well as replenishment of energy stores it is termed the master recovery hormone.

The dual activation of mTOR by protein as well as independently by carbohydrate via insulin release is a primary reason why a protein drink actually is less effective than a carb-protein drink in building lean body mass. Studies have shown that a carb-protein drink is 37% more effective than a protein drink alone in stimulating protein synthesis and building lean body mass. Understanding how specific nutrients affect key cellular processes enables us to optimize our recovery nutrition.

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