A MEDITERRANEAN diet high in olive oil, nuts, fish, and fresh fruits and vegetables may help prevent heart disease and strokes, according to a new large study from Spain.
Past research has suggested people who eat a Mediterranean-like diet have healthier hearts, but those studies could not rule out that other health or lifestyle differences had made the difference.
For the new trial, 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 disease — with a good diet," says Dr 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 personalised advice 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 any type of cardiovascular disease.
People on both Mediterranean diets were 28%-30% less likely to develop cardiovascular disease than those on the general low-fat diet, the researchers report in the New England Journal of Medicine.
The new study is the first randomised trial of any diet pattern to show benefit among people initially without heart disease, says Dr Dariush Mozaffarian, who studies nutrition and cardiovascular disease at the Harvard School of Public Health in Boston.
No single ingredient
It’s the blend of Mediterranean diet components — not one particular ingredient — that promotes heart health, according to Dr Martinez-Gonzalez.
"The quality of fat in the Mediterranean diet is very good," he says. "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," including legumes and fruits as desserts.
Dr Mozaffarian, who was not involved in the new research, agrees, and says: "I think it’s a combination of what’s eaten and what’s not eaten."
Things that are discouraged are refined breads and sweets, sodas and red meats and processed meats, he says.
"The combination of more of the good things and less of the bad things is important."
Dr Martinez-Gonzalez suggests 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, says Teresa Fung, a nutrition researcher at Simmons College in Boston who was also not on the study team.
"All of these steps are making, at the end of the day, a big difference," Dr Martinez-Gonzalez says.
Prof Fung points out many people in the new trial were already on medications 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 says.
That’s likely the case for people without heart risks — including high blood pressure or cholesterol — as well, Prof Fung says.
"This is a high-risk group, but I don’t think people should wait until they become high-risk in order to change," she says.