A combination of unsaturated fats and nitrite-rich vegetables, including olive oil and lettuce, may help protect against hypertension, according to a new study. The study, which was led by King’s College London, helps to explain why prior studies have shown that a Mediterranean diet can be useful for reducing blood pressure.

The findings were published in the journal Proceedings of the National Academy of Sciences.

An average Mediterranean diet generally contains unsaturated fats, such as those that are found in olive oil, nuts, and avocados, as well as vegetables including celery, spinach, and carrots that contain high amounts of nitrites and nitrates.

According to the researchers, the pairing of fats and greens creates a compound called nitro fatty acid, which helps to relax blood vessels and lower blood pressure, both of which are crucial components of heart health.

The team tested their theory by feeding mice with high blood pressure omega-6 fatty acids that are found in olive oil. The researchers also added sodium nitrite to the mice’s diets to synthesize the pairing of olive oil and vegetables. By the end of the five-day intervention, the mice had lower blood pressure and higher levels of nitro fatty acids.

Philip Eaton, Professor of Cardiovascular Biochemistry at King’s College London, said in a statement, “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.”

According to the BBC, the Mediterranean diet is inspired by traditional cuisine in countries including Greece, Spain, and Italy, and has long been associated with good physical and heart health. The diet primarily consists of vegetables, fresh fruit, wholegrain cereal, olive oil and nuts, along with poultry or fish, with minimal amounts, if any, of red meat, butter, and animal fats.