MICHAEL MAZZULLA, SIDNEY ABOU SAWAN, JEFFREY E. PACKER, DANIEL R. MOORE*
*Corresponding author
University of Toronto, Faculty of Kinesiology and Physical Education, 55 Harbord St., Toronto, Ontario, M5S 2W6, Canada

Abstract

Skeletal muscle is a dynamic tissue that is critical to the physical health and function of humans. The maintenance of muscle mass is largely dependent on the process of muscle protein synthesis (MPS), which is nutritionally regulated by the provision of amino acids in the form of dietary protein and can be augmented by prior contractile activity (e.g. exercise). However, not all proteins are created equally in their ability to enhance MPS. Contemporary research has revealed that to optimally stimulate MPS in young and old adults, ~0.25g/kg and ~0.4g/kg, respectively, of leucine-rich, rapidly digested protein should be consumed at rest and/or after exercise. The present review will briefly discuss current science that underpins these “muscle-centric” recommendations for dietary protein.

INTRODUCTION

In humans, skeletal muscle mass is a critical determinant of physical health and function. In addition to its obvious role of converting chemical energy to mechanical work, skeletal muscle is also an important metabolic tissue contributing significantly to the basal metabolic rate (and hence energy balance) and the postprandial metabolism of glucose and fat. As such, an adequate quantity and quality of muscle mass is important for individuals of all ages to maintain metabolic health and functional capacity.

Similar to all proteins in the body, skeletal muscle is a dynamic tissue that is constantly being remodelled through the continuous and simultaneous processes of protein synthesis (MPS) and protein breakdown (MPB). This “turnover” functions to break down old and/or damaged proteins and synthesize new ones in their place. The net protein balance (i.e. the algebraic difference between MPS and MPB) determines whether there is a gain, no change, or loss in muscle protein and, ultimately, lean body mass.

MPS is the more highly regulated variable in healthy humans and is responsive to both the nutrient environment and the ac ...