Influence of dietary thermally oxidized soybean oil on the oxidative status of rats of different ages.

Young and aging rats were fed for different periods (10, 90, 180 and 365 days) diets containing 15% of fresh or heated soybean oil. Thiobarbituric reactive substances (TBA-RS), lipofuscin, superoxide dismutase (SOD), vitamin A, vitamin E and microsomal and mitochondrial fatty acids in liver, brain and serum were measured. Heated oil diets induced significant increase of TBA-RS levels in liver, with earlier effects in aging rats and affected SOD activity in aging rats only after a long period of feeding. Circulating and stored vitamin A were reduced in both young and aging rats, with earlier effects in young animals. Serum and liver vitamin E was significantly reduced in all test groups. The results indicate that heated unsaturated oil produces reduction in the antioxidative defense system and that vitamin E status is the earliest indicator of the oxidative effect regardless of age.