There seems to be no doubt that the Mediterranean diet can help stave off heart disease. How it does so has not been fully understood, but a new study may shed some light on the question.

The mainstays of the Mediterranean diet include generous amounts of fruits, vegetables, whole grains, legumes and olive oil, along with moderate portions of fish, dairy products, and wine.

So once again, Mom’s advice to eat your vegetables stands the test of time. Only now we know that adding a splash of olive oil may make them even better for you.

It’s the combination of vegetables and unsaturated fats, which appears to help manage blood pressure and reduce the risk of heart disease, the researchers found.

When nitrogen-containing vegetables, such as leafy greens, celery, or carrots, are combined with unsaturated fats, like those present in olive oil, nuts, and fish oils, the combination produces a group of nitro fatty acids that block an enzyme and help to lower blood pressure.

The study compared normal mice with mice genetically engineered to be resistant to the effects of nitro fatty acids. When given an enzyme inhibitor, normal mice experienced a decrease in blood pressure, while the experimental mice did not. And despite being fed foods that combine to make nitro fatty acids, the experimental mice maintained their high blood pressure. However, when normal mice were fed the same diet, the nitro fatty acids lowered their blood pressure.

According to a statement by researcher Philip Eaton, Professor of Cardiovascular Biochemistry at King’s College, London, “The findings of our study 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.”

Though the discovery was made in mice, humans have the same key enzyme — soluble epoxide hydrolase. Eaton is hopeful the results will be replicated in human studies.

Approximately a third of American adults have high blood pressure, sometimes dubbed the "silent killer" because there are usually no signs or symptoms. Having high blood pressure increases the risk for heart disease and stroke. Increasingly, experts are pointing to diet as a way to help manage the disease.

So once again, Mom’s advice to eat your vegetables stands the test of time. Only now we know that adding a splash of olive oil may make them even better for you.

The study is published in the Proceedings of the National Academy of Sciences.