DIETARY NON-TOCOPHEROL ANTIOXIDANTS PRESENT IN EXTRA VIRGIN OLIVE INCREASE THE RESISTANCE OF LOW-DENSITY LIPOPROTEINS TO OXIDATION IN RABBITS

Consumption of a range of dietary antioxidants may be beneficial in pr otecting low density lipoprotein (LDL) against oxidative modification, as studies hale demonstrated that antioxidants other than vitamin E m ay also function against oxidation of LDL in vitro. In the present stu dy, the effect of polyphenol antioxidants on the susceptibility of LDL to copper-mediated oxidation was investigated after feeding semi-puri fied diets to 3 groups of New Zealand white (NZW) rabbits. All diets c omprised 40%; energy as fat with 17%, energy as oleic acid. Dietary fa tty acid compositions were identical. Oils with different polyphenol c ontents were used to provide the dietary source of oleic acid - refine d olive oil, extra virgin olive oil and Trisun high oleic: sunflower s eed oil. Polyphenolic compounds (hydroxytyrosol and p-tyrosol) could o nly be detected in the extra virgin olive oil. Vitamin E was equalised in all diets. LDL oxidizability in vitro was determined by continuous ly monitoring the copper-induced formation of conjugated dienes after 6 weeks of experimental diet feeding. The lag phase before demonstrabl e oxidation occurred was significantly increased in the high polypheno l, extra virgin olive oil group (P < 0.05) when compared with combined results from the low polyphenol group (refined olive oil and Trisun). even though the LDL vitamin E concentration in the high polyphenol gr oup was significantly lower. The rare of conjugated diene formation wa s not influenced by the presence of dietary polyphenols. Results demon strate that antioxidants, possibly phenolic compounds which are presen t only in extra virgin olive oil, may contribute to the endogenous ant ioxidant capacity of LDL, resulting in an increased resistance to oxid ation as determined in vitro.