Elevation of the Mitochondrial Oxidative Activity of Rat Liver by Long-Term Intake of a High-Fat Diet Based on Beef Tallow or Safflower Oil.

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Using rats we examined the effects on liver mitochondrial functions of the long-term intake of a high-fat diet based on beef tallow or safflower oil. Forty-eight rats were divided into three dietary groups: a low-fat diet group and two high-fat ones (beef tallow and safflower oil). The low-fat diet provided 7, 73, and 20% of the total energy as fat, carbohydrate, and protein, respectively; and two high-fat diets, 45, 35, and 20% of energy, respectively. Rats were isoenergetically fed the appropriate diet for 4 months. The state-3 respiration of the mitochondria was significantly higher in the two high-fat diet groups than in the low-fat diet group, when both succinate and β-hydroxybutyrate were used as substrates for the respiration. However, there was no difference between the two high-fat diet groups. The groups were ranked in terms of cytochrome a content in their mitochondria as follows: low-fat diet group<beef tallow diet group<safflower oil diet group. The citrate synthase activity of the liver was also significantly higher in the two high-fat diet groups than in the low-fat one, but no difference was obtained between the two former. However, the mitochondrial DNA concentration in liver was not different among the three dietary groups. From these results, we conclude that long-term intake of high-fat diets increases the oxidative activity of liver mitochondria and that differences in the type of dietary fatty acids do not markedly alter mitochondrial functions.