We’ve all heard that the Mediterranean diet—rich in olive oil and vegetables—is good for our hearts, and now researchers believe they’ve finally found the “secret ingredient” that gives this diet such a powerful effect on health and longevity.

When the unsaturated fat in olive oil meets the naturally occurring nitrates and nitrates that many Mediterranean vegetables are rich in (like tomatoes, eggplant, garlic and leafy greens), a special kind of molecule is produced: “nitro fatty acids.” Beneficial omega-6 fats are normally broken down in the body by an enzyme called epoxide hydrolase, but these nitro fatty acids block the action of this enzyme. As a result, the “good fats” stay in the blood longer, where they lower blood pressure.

Researchers from King’s College London and the University of California, Davis used genetically engineered mice to figure out how the biochemical process worked. But they think it’s very likely that a similar mechanism occurs in people, because the epoxide hydrolase enzyme is virtually identical between mice and humans. To put nitro fatty acids to work in your diet, eat as many veggies as possible, especially lettuce and other salad greens. Nuts and avocados can fill the same role as olive oil.

(Source: Proceedings of the National Academy of Sciences, 2014; doi: 10.1073/pnas.1402965111 [link].)