Effects of dietary protein and fat level on oxidative phosphorylation in rat heart mitochondria

The effect of dietary protein and fat levels on cardiac mitochondrial oxidative phosphorylation was assessed polarographically. Weanling rats were fed on semi-purified diets containing different protein levels (10, 30, 50 and 70%) on a gross energy basis (PGE) for 9, 23 and 58 d. Cardiac mitochondria isolated from rats fed on a 70% PGE diet for 23 d exhibited significantly reduced ADP:oxygen (ADP:O) values compared with mitochondria from rats fed on a low-protein diet. Feeding low-protein diets for 58 d increased the ADP: O value. When the dietary fat level was altered to provide (% PGE: % fat-energy): 30:14, 30:30, 70:14, 70:30, feeding 70% PGE diets reduced the ADP:O value compared with the 30% PGE level, but no difference was observed between low-fat and high-fat groups. These results indicate that the impaired ADP: O value for rats fed on very-high-protein diets was not due to the dietary fat level but that the level of dietary protein is an important determinant of oxidative phosphorylation in rat heart mitochondria.