Effects of Varying Energy Deficits on Protein Turnover At Rest and Carbohydrate Oxidation During Steady-state Exercise

This randomized, parallel study will examine the effects of energy balance and varying magnitudes of energy deficit on 1) the protein kinetic responses to consuming high quality protein and 2) carbohydrate oxidation during steady-state exercise. Healthy adults, representative of active duty military personnel, will complete a 2 d energy balance phase followed by a randomly assigned, 5 d energy deficit phase (n=15 per group; 20%, 40% and 60% energy deficit). At the end of each energy phase the effects of energy balance and energy deficit severity on resting postabsorptive (fasting) and postprandial (after consuming ~34 g protein) muscle protein synthesis (MPS) and whole-body protein synthesis, breakdown, and balance (synthesis - breakdown) will be determined. On the next day, the effects energy balance and energy deficit severity on carbohydrate oxidation during steady-state exercise will be determined. Primary study procedures include anthropometric and body composition measures, resting metabolic rate measures, aerobic exercise, tightly controlled diet and exercise interventions, repeated blood sampling, stable isotope infusion, stable isotope ingestion, and percutaneous muscle biopsies. The following hypotheses will be tested: 1) Δ (postprandial - postabsorptive) MPS and Δ whole-body protein balance at rest will progressively decrease as magnitude of energy deficit increases and 2) exogenous carbohydrate oxidation will be higher and endogenous carbohydrate oxidation will be lower during steady-state exercise as magnitude of energy deficit increases.