A Mediterranean diet high in olive oil, nuts, fish and fresh fruits and vegetables may help prevent heart disease and strokes, according to a large study from Spain.
Past research suggested people who eat this type of diet have healthier hearts, but those studies couldn't rule out that other health or lifestyle differences had made the difference.
But for the new trial, written up in the New England Journal of Medicine, researchers randomly assigned study volunteers at risk of heart disease to a Mediterranean or standard low-fat diet for five years, allowing the team to single out the effect of diet in particular.
"This is good news, because we know how to prevent the main cause of deaths - that is cardiovascular diseases - with a good diet," said Miguel Angel Martinez-Gonzalez, who worked on the study at the Universidad de Navarra in Pamplona.
He and colleagues from across Spain assigned almost 7,500 older adults with diabetes or other heart risks to one of three groups.
Two groups were instructed to eat a Mediterranean diet - one supplemented with extra-virgin olive oil and the other with nuts, both donated for the study - with help from personalized advice and group meetings. The third study group ate a "control" diet, which emphasized low-fat dairy products, grains and fruits and vegetables.
Over the next five years, 288 study participants had a heart attack or stroke, or died of any type of cardiovascular disease.
People on both Mediterranean diets, though, were 28 to 30 percent less likely to develop cardiovascular disease than those on the general low-fat diet, the researchers said.
It's the blend of Mediterranean diet components, and not one particular ingredient, that promotes heart health, according to Martinez-Gonzalez.