Eur J Nutr (2004) 43: 140 –147 DOI 10.1007/s00394-004-0452-8 ORIGINAL CONTRIBUTION Jaume Marrugat María-Isabel Covas Montserrat Fitó Helmut Schröder Elisabet Miró-Casas Eva Gimeno M.Carmen López-Sabater Rafael de la Torre Magí Farré and the members of the SOLOS Investigators* Effects of differing phenolic content in dietary olive oils on lipids and LDL oxidation A randomized controlled trial EJN 452 Received: 4 April 2003 Accepted: 19 September 2003 Published online: 6 January 2004 J. Marrugat · M.-I. Covas () · M. Fitó · H. Schroeder Lipids and Cardiovascular Epidemiology Research Unit Institut Municipal d’Investigació Mèdica Carrer Dr Aiguader 80 08003 Barcelona, Spain Tel.: +34-93/221-1009 Fax: +34-93/221-3237 E-Mail: mcovas@imim.es J. Marrugat · M. Farré Universitat Autònoma de Barcelona Barcelona, Spain E. Miró-Casas · R. de la Torre · M. Farré Pharmacology Research Unit Institut Municipal d’Investigació Médica Barcelona, Spain E. Gimeno · M. C. López-Sabater Dept. of Nutrition and Bromatology Pharmacy Faculty. University of Barcelona 08028 Barcelona, Spain R. de la Torre Universitat Pompeu Fabra Barcelona, Spain * Participants of the SOLOS-Investigation are listed in the Appendix. ■ Summary Background Evidence from in vitro studies suggests that antioxidant olive oil phenolic com- pounds can prevent LDL oxidation. However, in vivo evidence in sup- port of this hypothesis is sparse. Aim of the study to establish the antioxidant effect of olive oils with differences in their phenolic com- pounds content in humans Meth- ods A controlled, double blind, cross-over, randomized, clinical trial using three similar olive oils with increasing phenolic concen- tration (from 0 to 150 mg/Kg) was conducted in 30 healthy volunteers. Olive oils were administered over three periods of 3 weeks preceded by two-week washout periods. Re- sults Urinary tyrosol and hydroxy- tyrosol increased (p < 0.020), in vivo plasma oxidized LDL de- creased (p = 0.006), and ex vivo re- sistance of LDL to oxidation in- creased (p = 0.012) with the pheno- lic content of the olive oil administered. After virgin olive oil administration, an increase (p = 0.029) was observed in HDL cholesterol levels. Conclusions Sus- tained consumption of virgin olive oil with the high phenolic content was more effective in protecting LDL from oxidation and in rising HDL cholesterol levels than that of other type of olive oils. Dose-de- pendent changes in oxidative stress markers, and phenolic compounds in urine, were observed with the phenolic content of the olive oil ad- ministered. Our results support the hypothesis that virgin olive oil con- sumption could provide benefits in the prevention of oxidative processes. ■ Key words olive oil – phenolic compounds – tyrosol – oxidized LDL – Mediterranean diet – HDL cholesterol Introduction There is a growing evidence that the Mediterranean diet, in which olive oil is the main source of fat, has a benefi- cial effect on diseases associated with oxidative damage such as coronary heart diseases (CHD) and cancer, and on aging [1–3]. The Mediterranean type diet has been shown to reduce the number of recurrences in patients with myocardial infarction [3] and is assumed to ac- count in part for the low CHD incidence and mortality rates observed in southern European Mediterranean countries [4]. Phenolic compounds are antioxidant agents present in several foods of the Mediterranean diet among which virgin olive oil stands out. The biological benefits of olive oil consumption in preventing low-density lipoproteins (LDL) from oxidation could be linked both