Dietary fiber reduces the antioxidative effect of a carotenoid and α-tocopherol mixture on LDL oxidation ex vivo in humans
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Background: Antioxidant concentrations in low density lipoproteins (LDL) are an important determinant for their susceptability to oxidation and can be modulated by dietary intake. Aim of the study: In the present study, the influence of dietary fiber on the antioxidant enrichment and the oxidation resistance of LDL after antioxidant supplementation is investigated. Method: An antioxidant supplement consisting of β-carotene, lycopene, lutein, canthaxanthin and α-tocopherol was given to six young women together with a standard meal. Using a cross-over study design, each subject received the standard 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 measured. Results: Eight, 10, and 24 hours after antioxidant supplementation the isolated LDL revealed significantly (p < 0.05) increased antioxidant concentrations; addition of pectin, guar, or cellulose to the meal depressed this increase. Concomitantly, the observed increase in the resistance of LDL against oxidation (measured as lag phase) was lower with dietary fiber supplementation 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%, 22%, and 18%, respectively. Conclusions: These results indicate that dietary fiber supplementation decreases the antioxidative effect of a supplement consisting of carotenoids and α-tocopherol in LDL, an effect that is likely to be mediated by a reduced bioavailability of these antioxidants in the gut.
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