Effects of Short-term Energy Deficit on Muscle Protein Turnover
Condition: Obesity
Study type: Interventional

Summary: 
      Weight loss through energy restriction results in the loss of both fat and muscle mass.
      Muscle mass is important for mobility, strength, glucose control and energy expenditure, and
      therefore the retention of muscle mass during energy restriction is an important goal. The
      retention of muscle mass depends on the balance between muscle protein synthesis (MPS) and
      muscle protein breakdown (MPB). It is well known that MPS is reduced during weight loss,
      however the effect of weight loss on MPB is currently a topic of debate. The purpose of this
      study is to assess the effect of short-term (10 day) weight loss (40% energy deficit) on both
      MPS and MPB in order to gain insight into the mechanisms causing muscle loss during energy
      restriction. In addition, the effect of resistance exercise and protein (both known to
      preserve muscle mass) on MPS and MPB will be examined
    

Detailed description: 
      An undesirable consequence of energy restriction is the loss of muscle mass. Muscle mass is
      determined by the the rates of two processes: muscle protein synthesis and muscle protein
      breakdown. It has been consistently shown that a reduced rate of muscle protein synthesis
      exists during energy restriction. However, it is currently unclear whether an increase in
      muscle protein breakdown also contributes to muscle mass loss. In addition, the effect of
      high protein diets and resistance exercise on muscle protein turnover during energy
      restriction, two interventions known to preserve muscle, remains to be investigated.We aim to
      demonstrate that the decrease in muscle protein synthesis is the main contributor to a
      negative protein balance during energy restriction. In addition, we hope to show that a
      higher-protein diet (2.4g/kg/d versus 1.2g/kg/d) and the addition of resistance exercise can
      help to maintain the muscle protein synthesis rate and thereby improve negative protein
      balance.The present study will be designed as a parallel group randomized controlled trial.
      Subjects will be given pre-packaged diets (Copper County Foods) to consume which will put
      them in a relative energy deficit of 40% per day. Based on random assignment, these subjects
      will either consume an adequate protein diet (1.2g/kg/d) or a high protein diet (2.4g/kg/d)
      for 10 consecutive days. Participants in the adequate protein diet will consume a ratio of
      50:35:15 (carbohydrates:fat:protein) while subjects within the high protein diet will consume
      a ratio of 50:15:35 (carbohydrates:fat:protein). Subjects will undergo testing at baseline
      and following a 10 day dietary and unilateral resistance exercise intervention. Testing will
      consist of muscle and blood samples. Muscle protein synthesis and muscle protein breakdown
      will be measured using stable isotope tracers that are orally ingested (deuterated water) or
      infused into an antecubital vein (labelled phenylalanine tracers) before and after the 10 day
      diet.
    

Intervention name(s): Energy Restriction
Intervention type(s): Other
Intervention description(s): All meals will be provided for the duration of the energy restriction intervention and the energy deficit will be calculated based on estimated energy requirements by indirect calorimetry to provide 60% of energy requirements. In addition, one leg will be assigned to perform resistance exercise for 5 days during the 10 day energy deficit.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Protein synthesis; Protein breakdown; Muscle; Energy restriction