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Olive oil is known as one of the best sources of monoun­sat­u­rated fatty acids, a type of fat that has been shown to improve blood cho­les­terol levels. It was thought that the pro­tec­tive qual­i­ties of olive oil were due mainly to the pres­ence of this type of fat, how­ever new research shows that its antiox­i­dant con­tent is equally impor­tant. According to new data pub­lished in Clinical Nutrition, daily doses of olive oil that is rich in polyphe­nols (a type of antiox­i­dant) may pro­tect from ath­er­o­scle­ro­sis (hard­en­ing of the arter­ies).

The results came from the EurOlive Study, which involved researchers from uni­ver­si­ties in five European coun­tries, and was aimed at assess­ing the ben­e­fi­cial effects of olive oil on human health. The researchers recruited 200 healthy men and ran­domly assigned them to one of three groups to con­sume 25 mls of olive oil every day with dif­fer­ent amounts of polyphe­nols.

The olive oils that were admin­is­tered included refined olive oil, which had a low polyphe­nol con­tent, common olive oil, which had a medium polyphe­nol con­tent and virgin, which had high polyphe­nol con­tent. The results showed that the con­sump­tion of polyphe­nol rich olive oil increased the levels of an anti­body that reduces levels of oxi­dized LDL cho­les­terol (bad cho­les­terol), and is con­sid­ered a risk factor of artery hard­en­ing and heart dis­ease.

This was not the first time that olive oil polyphe­nols have been found to have a pro­tec­tive effect against oxida­tive damage, pre­vi­ous stud­ies have also shown a pos­i­tive effect. However, there were ques­tions as to whether real life doses of olive oil can achieve this effect and whether the par­tic­u­lar olive oil con­sumed is in fact high in polyphe­nols.

In this study the researchers had the sub­jects con­sume about 2 table­spoons of olive oil a day, a rea­son­able amount for non-Mediterranean coun­tries. Inhabitants of Mediterranean coun­tries have a much higher intake. For exam­ple Greeks who have the high­est intake of olive oil per person in the world con­sume about 70 mls a day, while Spaniards and Italians include about 35 mls a day.

The other issue is the polyphe­nol con­tent. Studies have shown that extra virgin olive oil has more polyphe­nols than other olive oils that are processed. Storage con­di­tions also play an impor­tant role. Oil that is stored in a dark, cool spot in a dark con­tainer retains more of its antiox­i­dants. Long stor­age times reduce the antiox­i­dant con­tent as well; the longer olive oil sits in a bottle unused, the more polyphe­nols it loses.

• The effect of olive oil polyphe­nols on anti­bod­ies against oxi­dized LDL. A ran­dom­ized clin­i­cal trial Authors: O. Castaner, M. Fito, M.C. Lopez-Sabater, H.E. Poulsen, et al. for the EUROLIVE Study Group