PLASMA AND LIPOPROTEIN LIPID-PEROXIDATION IN HUMANS ON SUNFLOWER AND RAPESEED OIL DIETS

The effects of natural mixed diets on lipid peroxidation were investig ated in humans. In the first study, 59 subjects were fed a rapeseed oi l-based diet rich in monounsaturated fatty acids (MU FA) and a sunflow er oil-based diet rich in polyunsaturated fatty acids (PU FA) in a cro ss-over manner for three and a half weeks. The lipid peroxidation prod ucts in plasma were determined by measuring conjugated dienes and malo ndialdehyde (MDA). In a second study, plasma thiobarbituric acid react ive substances (TEARS), lipid hydroperoxides, and the susceptibility o f very low density lipoprotein + low-density lipoprotein (LDL) to in v itro oxidation were measured from subjects fed similar MUFA and PUFA d iets for six week diets. No significant differences in plasma MDA or c onjugated diene concentrations were found after the rapeseed oil diet or the sunflower oil diet in Study 1. In the second study, a small but significant decrease (P < 0.05) in both lipid hydroperoxides and TEAR S was observed in the LDL fraction after the sunflower oil diet. The i n vitro oxidation gave opposite results, showing increased oxidation a fter the sunflower oil diet. Despite a high intake of alpha-tocopherol during the oil periods, no increase in plasma alpha-tocopherol was no ticed in either study. The results suggest that moderate changes in th e fatty acid composition in the Western-type diet may be adequate to a ffect lipoprotein susceptibility to oxidation in vitro, but there is c onsiderable disparity with some indices of in vivo lipid peroxidation.