A new study from the University of Granada shows that cooking with extra virgin olive oil increases the phenol content over that of the raw vegetable. Some in the past have thought that the cooking process destroys the polyphenols in EVO where this study shows the polyphenols are absorbed by the vegetables. The cooking method that displayed the highest level of increase was deep frying, at the same time it showed the highest increase in fat content. Sauteing in EVO showed a moderate increase in phenol content. While boiling in water showed a decrease in phenol content. While not addressed by the study, the water from boiling vegetables is generally considered to be full of nutrients and can be used beneficially in other ways, such as for soup.
They also found that cooking in EVO actually breaks some bonds that free up more polyphenols. This shows evidence that disputes the theory that the polyphenols in real extra virgin olive oil are destroyed during the cooking process.