A Mediterranean diet high in olive oil, nuts and fish as well as fresh fruits and vegetables can help prevent heart disease and strokes, according to a large study from Spain.
Past research suggested people who follow this diet have healthier hearts, but those studies couldn't rule out whether other health or lifestyle differences had made the difference.
But for the new trial, which recently appeared 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 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 personal advisers and group meetings. The third study group ate a ``control'' diet, which emphasised 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 a cardiovascular disease.
People on both Mediterranean diets, though, were 28-30% less likely to develop cardiovascular disease than those on the general low-fat diet, the researchers said.
The new study is the first randomised trial of any diet pattern to show benefit among people initially without heart disease, said Dariush Mozaffarian, who studies nutrition and cardiovascular disease at the Harvard School of Public Health.
It's the blend of the Mediterranean diet components, rather than one particular ingredient, that promotes heart health, according to Martinez-Gonzalez.
``The quality of fat in the Mediterranean diet is very good,'' he said.
``This good source of calories is replacing other bad sources of calories. In addition, there is a wide variety of plant foods in the Mediterranean diet,'' he added, including legumes and fruits as desserts. He suggested that people seeking to improve their diet start with small changes, such as forgoing meat one or two days a week, cooking with olive oil and drinking red wine with meals rather than hard alcohol.
Replacing a high-carbohydrate or high-saturated fat snack with a handful of nuts is also a helpful change, experts recommend.
``I think it's a combination of what's eaten and what's not eaten,'' said Mozaffarian, who wasn't involved in the study. ``Things that are discouraged are refined breads and sweets, sodas and red meats and processed meats.
``The combination of more of the good things and less of the bad things is vitally important.''
Teresa Fung, a nutrition researcher at Simmons College in Boston, Massachussetts, said that many people in the trial were already on medication, such as statins and diabetes drugs.
``The way I see it is, even if people are on medication already, diet has substantial additional benefit,'' she added.
``This is a high-risk group, but I don't think people should wait until they become high-risk in order to change.''
