The following article by Alice. G Walton is reprinted from Forbes, May 20, 2014.

New research in Proceedings of the National Academy of Sciences looks at the effect of the Mediterranean diet on heart health—and the verdict is favorable. But even more than that, the study lays out exactly why olive oil and greens are together so beneficial for the heart.

Until now, researchers hadn’t quite been able to explain why a diet as high in fat as the Mediterranean diet is linked to cardiovascular health. Researchers have wondered what exactly it is about the fats that helps the heart, and now they’ve arrived a pretty convincing mechanism to explain it.

The trick is to create a “fusion” of the healthy fats in, say, olive oil and the nitrites and nitrates in greens like spinach, celery, and carrots, which make up a large part of the Mediterranean diet. This fats–greens pairing, according to the researchers, creates a compound—nitro fatty acid—that has the effect of relaxing blood vessels and bringing down blood pressure, which are key components of heart health.

To test the theory, the team fed mice—with high blood pressure—the omega-6 fatty acids found in olive oil. They also added to their diets sodium nitrite, in order to mimic the pairing of olive oil and veggies. Indeed, not only was the level of nitro fatty acids higher in these mice, but their blood pressure was lower at the end of the 5-day intervention. And when the researchers used a strain of mice that were resistant to the effects of the nitro fatty acids, their blood pressure did not change.

Though the research was done in mice, the mechanism likely applies to people, too. Earlier research has pointed to the benefits of olive oil and nuts on cardiovascular health in humans.

“The findings of our study,” said study author Philip Eaton, “help to explain why previous research has shown that a Mediterranean diet supplemented with extra-virgin olive oil or nuts can reduce the incidence of cardiovascular problems like stroke, heart failure and heart attacks.” Avocados may work too, the team told the BBC, since they also contain healthy unsaturated fats.