Supplementation of protein-free diet with whey protein hydrolysates prevents skeletal muscle mass loss in rats

Abstract Muscle mass loss is induced by aging, several catabolic diseases, and malnutrition. It is well known that ingestion of whey protein and its hydrolysates (WPH) is effective in stimulating muscle protein synthesis. However, these studies focused on the acute up-regulation of muscle protein synthesis, and few studies have investigated the effect of whey protein and WPH on muscle mass during chronic malnutrition. The aim of the present study was to investigate the effect of 7 days supplementation of whey protein and WPH on muscle reduction in Wistar rats fed a protein-free (PF) diet. Wistar rats were fed either a standard diet (containing 20% protein) or a PF diet during the experimental period. Those fed a PF diet received a dietary supplement containing an amino acid mixture, whey protein, or WPH for 7 days. The weight of the extensor digitorum longus decreased in rats fed a PF diet supplemented with the amino acid mixture or the whey protein. However, this decrease was partially but significantly suppressed in the group fed the WPH supplement. Additionally, administration of WPH induced a postprandial increase in plasma essential amino acids, branched-chain amino acids, and leucine concentration compared with animals fed the amino acid mixture or the whey protein. These results suggest that 7 days supplementation of the diet with WPH suppressed muscle weight loss in rats fed a PF diet.