Extra virgin olive oil phenols and markers of oxidation in Greek smokers: a randomized cross-over study

Objective: To examine the effect of a low phenol olive oil and high phenol olive oil on markers of oxidation and plasma susceptibility to oxidation in normolipaemic smokers. Design: Randomized single-blind cross-over trial with two intervention periods. Setting: The Medical School and University Hospital of the University of Crete, Heraklion, Crete, Greece. Subjects: Twenty-five healthy males and females completed the study. Interventions: Each intervention was of three weeks duration and intervention periods were separated by a two week washout. Seventy grams of extra virgin olive oil was supplied to each subject per day in the intervention periods. The olive oils supplied differed in their phenol content by 18.6 mg/day. Two fasting venous blood samples were taken at the end of each intervention period. Results: The markers of antioxidant capacity measured in fasting plasma samples (total plasma resistance to oxidation, concentrations of protein carbonyl as a marker of protein oxidation, malondialdehyde and lipid hydroperoxides as markers of lipid oxidation and the ferric reducing ability of plasma) did not differ significantly between the low and high phenol olive oil diets. Conclusions: No effect of olive oil phenols on markers of oxidation in smokers was detected. It may be that the natural concentrations of phenols in olive oil are too low to produce an effect in the post-absorptive phase. Possible reasons for period effects and interactions between diet and administration period need attention to aid further cross-over trials of this kind. Sponsorship: Unilever Research Vlaardingen, The Netherlands.