Purpose of review: Muscle protein synthesis (MPS) and muscle protein breakdown are simultaneous ongoing processes. Here, we examine evidence for how protein quality can affect exercise-induced muscle protein anabolism or protein balance (MPS minus muscle protein breakdown). Evidence is highlighted showing differences in the responses of MPS, and muscle protein accretion, with ingestion of milk-based and soy-based proteins in young and elderly persons.
Recent findings: Protein consumption, and the accompanying hyperaminoacidemia, stimulates an increase in MPS and a small suppression of muscle protein breakdown. Beyond the feeding-induced rise in MPS, small incremental addition of new muscle protein mass occurs following intense resistance exercise which over time (i.e. resistance training) leads to muscle hypertrophy. Athletes make use of the paradigm of resistance training and eating to maximize the gains in their skeletal muscle mass. Importantly, however, metabolically active skeletal muscle can offset the morbidities associated with the sarcopenia of aging such as type II diabetes, decline in aerobic fitness and the reduction in metabolic rate that can lead to fat mass accumulation.
Summary: Recent evidence suggests that consumption of different proteins can affect the amplitude and possibly duration of MPS increases after feeding and this effect interacts and is possibly accentuated with resistance exercise.