Increased oxidative properties of gastrocnemius in rats fed on a high-protein diet.

It has been reported that a high-protein diet containing 30% protein partially prevents skeletal muscle fiber type changes (slow to fast) under atrophic conditions. No studies have examined the detailed effects of dietary protein on the oxidative properties of skeletal muscles. We examined the effects of a high-protein diet on the oxidative properties of rat gastrocnemius. Nineteen male Wistar rats (5 weeks old) were divided into the following groups: (1) control diet [15% protein (15P); n=6], (2) 25% protein (25P; n=6) and (3) 35% protein (35P, n=7). After 4 weeks of feeding, succinate dehydrogenase (SDH) staining and myosin isoforms were analyzed, along with the expression of the major transcription-related molecules for fast-to-slow fiber transition, i.e., peroxisome proliferator-activated receptor gamma coactivator (PGC) 1 alpha and nuclear factor of activated T cells (NFAT) c1. SDH staining showed that the relative oxidative fiber content of the 35P group was significantly higher than that of the 15P group. The slow myosin heavy chain content in the 35P group was also higher than that in the 15P group. Western blotting analysis showed that the gastrocnemius of the 35P group contained significantly higher amounts of PGC1 alpha and NFATc1 than that of the 15P group. We conclude that a high-protein diet, i.e., 35% protein, induces oxidative properties in rat gastrocnemius.