Discussion
CVD
The present double-blind, cross-over, randomised controlled trial investigated the effect of 3-week daily consumption of either raw extra virgin HPOO (320 mg/kg, phenolic content; 60 ml, daily dose) or LPOO (86 mg/kg, phenolic content; 60 ml daily dose) on HDL-cholesterol efflux capacity and serum lipids in Australian adults with no previously diagnosed medical condition. Our results showed no significant differences in any of the examined biomarkers between the two treatment arms. A non-significant mean increase in HDL-cholesterol efflux capacity was observed within both the LPOO and HPOO groups for the total sample, while serum HDL-cholesterol increased significantly within both treatment arms. A small but significant increase in circulating LDL-cholesterol was also observed in the HPOO arm.Although an increase in HDL-cholesterol efflux capacity was observed within both arms in our study (+0·54 %, LPOO; +0·10 %, HPOO), this did not reach statistical significance which is inconsistent with previous studies. For example, Hernaez A beneficial effect of HPOO intake on HDL-cholesterol efflux capacity was also supported by a recent systematic review and meta-analysis, which examined the effect of HPOO The molecular mechanisms by which phenolic compounds promote cholesterol efflux still require further elucidation. These mechanisms involve the passive diffusion process as well as pathways that are mediated by the transmembrane transporters ABCA1, ABCG1 and the scavenger receptor B1. Specifically, ABCA1 facilitates cholesterol efflux from cells to lipid-poor apolipoproteins while ABCG1 and the scavenger receptor B1 receptor are responsible for the efflux of cholesterol from macrophages to HDLThe effect of the two kinds of OO on serum lipids was also examined in the current study. Results demonstrated that both extra virgin HPOO and LPOO consumption significantly increased circulating HDL-cholesterol after 3 weeks. There is evidence supporting the effect of OO polyphenols on serum HDL-cholesterol; however, the data are once again inconsistent. In 2015, a meta-analysis reported no effect of EVOO intake (150 mg/kg, phenolic content) on circulating HDL-cholesterol in both healthy and adults with CVDIt has been reported that the daily consumption of OO rich in polyphenols reduces LDL-cholesterol and improves lipoprotein-associated atherogenic ratiosWith regard to the dietary intake changes and any potential confounding effect caused by differences in dietary intake, the OLIVAUS study showed that both treatment oils equally increased the intake of energy and macronutrients (i.e. fatty acids), while no significant within-group changes or between-group differences were observed in the intake of foods high in polyphenols (online Supplementary Tables The findings of the present study should be interpreted in light of its strengths and limitations. A strength of this study was its randomised, cross-over double-blind, controlled design, which confers strong inter-individual variability. Another strength was that study participants retained their habitual diet, hence allowing us to directly assess the effects of OO intake. Furthermore, our findings indicate that a moderate concentration of OO polyphenols (i.e. 86 mg/kg) can still induce positive effects on CVD risk markers. These results, if verified in future studies, might have a direct impact on the OO industry and human nutrition. One of the study’s limitations is that although participant compliance to the intervention was overall high, measurements of compliance relied on self-reporting methods and were therefore subjective. Another limitation is the fact that there was only a 4-fold difference in the phenolic content between the HPOO and LPOO (320 mg/kg 