Extra-virgin olive oil（初榨橄榄油） can protect the liver from oxidative（氧化的） stress. Researchers writing in BioMed Central's open access journal Nutrition and Metabolism exposed rats to a moderately toxic herbicide known to deplete antioxidants（抗氧化剂） and cause oxidative stress, finding that those rats fed on a diet containing the olive oil were partially protected from the resulting liver damage. Mohamed Hammami from the University of Monastir, Tunisia and King Saud University, Riyadh, Saudi Arabia, worked with a team of researchers to carry out the experiments in a group of 80 rats. He said, "Olive oil is an integral ingredient in the Mediterranean diet. There is growing evidence that it may have great health benefits including the reduction in coronary heart disease（冠心病） risk, the prevention of some cancers and the modification of immune and inflammatory（炎症的） responses. Here, we've shown that extra virgin olive oil and its extracts protect against oxidative damage of hepatic（肝的） tissue".

The researchers separated the rats into a control group, an olive oil group, and 6 groups that were exposed to the herbicide '2,4-Dichlorophenoxyacetic acid' with or without either whole olive oil, or one of two oil extracts – the hydrophilic（亲水的） fraction or the lipophilic（亲油的） fraction. All rats given the herbicide showed signs of significant liver damage. However, extra virgin olive oil and hydrophilic fraction intake induced a significant increase in antioxidant enzyme activity and a decrease in markers of liver damage.

Speaking about the results, Hammami said, "The hydrophilic fraction of olive oil seems to be the effective one in reducing toxin-induced oxidative stress, indicating that hydrophilic extract may exert a direct antioxidant effect on hepatic cells. However, more detailed studies about the effect of antioxidant compounds separately and/or their interactions are necessary to substantiate these observations".