Vitamin E status and tissue fatty acid composition in rats fed a moderately oxidized soybean oil at low or high vitamin E supply

This study was performed to investigate the effect of feeding a moderately oxidized soybean oil on vitamin E status and tissue fatty acids in rats. Therefore, growing malt: rats were fed diets containing either a mixture of coconut oil and soybean oil (19:1, w:w), fresh soybean oil, or heated and air-treated soybean oil as sources of dietary fats over a period of 40 days. The lipids of those diets had a peroxide value of 5.1, 9.5, and 74 mEq O-2/kg, respectively, on average over the whole feeding period. Additionally, according to a bifactorial design, the vitamin E supply of the animals was varied (11 versus 511 mg alpha-tocopherol equivalents per kg of diet). In order to evaluate the effects of dietary fat and vitamin E supply on the vitamin E status, the tocopherol concentrations in plasma, liver, kidney, heart and adipose tissue were measured. As expected, the vitamin E supply had a marked effect on the vitamin E status. In contrast, feeding the moderately oxidized soybean oil did riot considerably affect the vitamin E status relative to feeding the fresh soybean oil. A slight drop in tocopherol concentrations was observed only in liver and plasma (at the low dietary vitamin E level) and in kidney (at the high dietary vitamin E level) whereas the tocopherol concentrations in the heart and adipose tissue remained completely unchanged by feeding the oxidized soybean oil in comparison to feeding the fresh soybean oil. The type of fatty acids ingested was a more important factor influencing the vitamin E status. In this respect, rats fed the coconut oil at both dietary vitamin E levels exhibited a slightly higher vitamin E status than those rats fed fresh or oxidized soybean oil. The fatty acid composition of liver total lipids was only slightly influenced by feeding the oxidized oil, and that of the erythrocyte membrane total lipids remained completely unchanged, by feeding the oxidized soybean oil in comparison with feeding the fresh soybean oil. This suggests that the dietary oxidized oil did not influence the fatty acid metabolism. On the other hand, among the groups fed soybean oil, a low dietary vitamin E level reduced levels of PUFA relative to a high dietary vitamin E level. This suggests a loss of PUFA by lipid peroxidation in rats fed a low vitamin E diet at a high intake of PUFA. Although feeding the oxidized soybean oil did not affect the fatty acid composition and the ratio between cholesterol and erythrocyte membranes, it increased the osmotic resistance against hemolysis during incubation in hypotonic solutions, regardless of the dietary vitamin E level. In conclusion, the study shows that a moderately oxidized oil has little effect on vitamin E status and fatty acid metabolism; however, as shown bt; the model of the osmotic fragility of erythrocytes, membrane properties can be influenced even by moderately oxidized oils.