Myofibrillar Protein Synthesis Following Ingestion of Soy Protein Isolate at Rest and After Resistance Exercise in Elderly Men

Knowledge of the capacity of proteins from different sources to stimulate myofibrillar protein synthesis (MPS) in the elderly is warranted in view of the importance of preserving skeletal muscle mass in ageing. This chapter shows that ingestion of 20 g and 40 g of soy protein isolate does not stimulate increased rates of MPS under resting conditions in the elderly. The mechanism(s) underpinning differences in the capacity of these proteins to support increased rates of MPS has not been fully elucidated. The greater rates of MPS observed with equivalent doses of whey as compared to soy protein suggest that protein source is an important factor in reaching and surpassing the anabolic threshold the higher leucine content and more rapid leucinemia with whey as opposed to soy may in part explain the observed differences in resting and post-exercise MPS between the two proteins.