Effects of Short-term Energy Deficit on Muscle Protein Turnover

Overview

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

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.