Effect of Supplementing a Mixed Macronutrient Beverage With Graded Doses of Leucine on Myofibrillar Protein Synthesis
Condition: Muscle Protein Synthesis
Study type: Interventional

Summary: 
      Muscle mass is normally maintained through the regulated balance between the processes of
      protein synthesis (i.e. making new muscle proteins) and protein breakdown (breaking down old
      muscle proteins). Proteins are composed of amino acids and we know that amino acids increase
      muscle protein synthesis. However, not all amino acids are the same. Essential amino acids
      are ones that must be consumed through food, while non-essential amino acids can be made by
      our body. Interestingly, the essential amino acids are all that are required to increase the
      rate of muscle protein synthesis. In addition, the essential amino acid leucine appears to be
      particularly important in regulating protein synthesis. However, how leucine is able to
      increase protein synthesis is not entirely understood. Previously, it has been shown that
      20-25 g of high-quality protein, such as that found in milk (whey), appears to be the amount
      of protein that maximizes the rate of muscle protein synthesis after performing a bout of
      resistance exercise. Thus, we aim to measure the synthesis of new muscle proteins after
      ingesting different amounts of protein and amino acids. We will measure muscle protein
      synthesis after consumption of the beverage a participant is randomized to in a leg that has
      done no exercise ( ie. a rested leg) and in the other leg that has done resistance exercise.
      Amino acids are 'strung-together' to make protein. The 'essential' amino acids must be
      consumed through food because our body cannot make them, thus they are consumed when you eat
      protein rich foods like milk or chicken. Leucine, isoleucine, and valine are simply 3 of the
      8 essential amino acids that make up dietary protein. Unlike essential amino acids,
      'non-essential' amino acids may be synthesized by the body, however they are also present in
      protein rich foods like chicken or milk. We aim to determine if it is the leucine content
      found in 25 g of whey protein that is primarily responsible for maximizing muscle protein
      synthesis at rest and following resistance exercise. We also wish to determine how muscle
      genes and metabolism respond to this protocol.
    

Detailed description: 
      The processes of muscle protein synthesis (MPS) and muscle protein breakdown (MPB) occur
      concurrently. This constant protein turnover allows the muscle fiber to change its protein
      structure if loading demands or diet changes. The plasticity of skeletal muscle to respond to
      altered loading and contractile patterns is evidence of the capacity for remodeling that a
      fiber can undergo. It is quite well documented for example that mitochondrial content
      increases with endurance-type work. In contrast, heavier loading leads to less change in
      mitochondrial content but increases in myofibrillar proteins. All of the aforementioned
      phenotypic adaptations represent a re-patterning of the muscle's genetic expression patterns,
      protein translation, and processes for breakdown of existing protein structures to 'insert'
      the new proteins. A persistent muscle protein turnover also provides for a constant mechanism
      of protein 'maintenance' by removing damaged proteins and replacing them with new proteins.
      Damage to proteins can come about through oxidation or simply mechanical damage due to high
      forces during lengthening contractions. Regardless of the mechanism the balance between the
      processes of muscle protein synthesis (MPS) and muscle protein breakdown (MPB) will determine
      the net gain, loss, or no change of proteins in the myofiber.
    

Intervention name(s): Positive Control; Negative Control; Low Protein Low Leucine Spike; Low Protein High Leucine Spike; Low Protein + High Leucine + BCAA Spike
Intervention type(s): Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement
Intervention description(s): Subject consumes 25g of whey protein following unilateral exercise; Subject consumes 6.25g of whey protein following unilateral exercise; Subject consumes 6.25g of whey protein plus 3g of leucine following unilateral exercise; Subject consumes 6.25g of whey protein plus 5g of leucine following unilateral exercise; Subject consumes 6.25g of whey protein plus 5g of leucine plus valine and isoleucine (BCAA) following unilateral exercise
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Basic Science
Keywords: Protein Turnover; Resistance Exercise; Whey Protein; Leucine