Equal Distributions of Dietary Protein Throughout the Day Maximizes Rat Skeletal Muscle Mass

Abstract

Americans consume small servings of protein early in the day, with over 60% of daily protein intake coming at dinner. How protein distribution effects muscle health is uncertain. This study evaluated effects of isonitrogenous whey protein diets in which the meal distribution of protein was either equal at breakfast, lunch, and dinner (16% protein at each) or unevenly distributed consisting of 8% whey protein at breakfast and lunch, and 27.5% at dinner. Adult rats (300g) were fed 3 meals/d for 10 wk. At 2 and 10 wk, rats were sacrificed after a 13hr fast or 90min afterconsuming the breakfast meal. Measurements included skeletal muscle weights, plasmainsulin, glucose, amino acids, muscle protein synthesis (MPS) determined by D5‐Phe incorporation and phosphorylation activation of initiation factors 4E‐BP1 and S6K. Results showed that the equally distributed whey protein group had significantly greater postprandial MPS after the breakfast meal and larger muscle mass than the unequally distributed treatment. MPS responses were closely related with changes in plasmaleucine and phosphorylation of 4E‐BP1 and S6K. These results suggest that protein distribution is a critical factor in determining efficiency of protein utilization and skeletal muscle health. Supported by the Egg Nutrition Center.