Dietary fiber reduces the antioxidative effect of a carotenoid and alpha-tocopherol mixture on LDL oxidation ex vivo in humans

Background: Antioxidant concentrations in low density lipoproteins (LDL) ar e an important determinant for their susceptability to oxidation and can be modulated by dietary intake. Aim of the study: In the present study, the i nfluence of dietary fiber on the antioxidant enrichment and the oxidation r esistance of LDL after antioxidant supplementation is investigated. Method: An antioxidant supplement consisting of p-carotene, lycopene, lutein, cant haxanthin and a-tocopherol was given to six young women together with a sta ndard meal. Using a cross-over study design, each subject received the stan dard meal without additional dietary fiber and enriched with pectin, guar, or cellulose in a random order. To determine the resistance of LDL against copper ion-induced oxidation, the formation of conjugated dienes was measur ed. Results: Eight, 10, and 24 hours after antioxidant supplementation the isolated LDL revealed significantly (p < 0.05) increased antioxidant concen trations; addition of pectin, guar, or cellulose to the meal depressed this increase. Concomitantly, the observed increase in the resistance of LDL ag ainst oxidation (measured as lag phase) was lower with dietary fiber supple mentation than that found without. On average, pectin, guar, and cellulose reduced the increase of the lag phase (measured without addition of dietary fiber) by 38%, 21%, and 18%, respectively. Conclusions: These results indi cate that dietary fiber supplementation decreases the antioxidative effect of a supplement consisting of carotenoids and a-tocopherol in LDL, an effec t that is likely to be mediated by a reduced bioavailability of these antio xidants in the gut.