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 suggested people who eat a Mediterranean-like diet have healthier hearts, but those studies couldn’t 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,” said 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 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.
As with many clinical trials, the observed rates of cardiovascular events were lower than anticipated, with reduced statistical power to separately assess components of the primary end point. However, favorable trends were seen for both stroke and myocardial infarction. We acknowledge that, even though participants in the control group received advice to reduce fat intake, changes in total fat were small and the largest differences at the end of the trial were in the distribution of fat subtypes. The interventions were intended to improve the overall dietary pattern, but the major between-group differences involved the supplemental items. Thus, extra-virgin olive oil and nuts were probably responsible for most of the observed benefits of the Mediterranean diets. Differences were also observed for fish and legumes but not for other food groups. The small between-group differences in the diets during the trial are probably due to the facts that for most trial participants the baseline diet was similar to the trial Mediterranean diet and that the control group was given recommendations for a healthy diet, suggesting a potentially greater benefit of the Mediterranean diet as compared with Western diets.
In conclusion, in this primary prevention trial, we observed that an energy-unrestricted Mediterranean diet, supplemented with extra-virgin olive oil or nuts, resulted in a substantial reduction in the risk of major cardiovascular events among high-risk persons. The results support the benefits of the Mediterranean diet for the primary prevention of cardiovascular disease.
People on both Mediterranean diets were 28 to 30 percent less likely to develop cardiovascular disease than those on the general low-fat diet, the researchers reported Monday in the New England Journal of Medicine.
The new study is the first randomized trial of any diet pattern to show benefit among people initially without heart disease, said Dr. Dariush Mozaffarian, who studies nutrition and cardiovascular disease at the Harvard School of Public Health in Boston.
NOT DUE TO SINGLE INGREDIENT
It’s the blend of Mediterranean diet components - not one particular ingredient - that promotes heart health, according to Martinez-Gonzalez.
“The quality of fat in the Mediterranean diet is very good,” he told Reuters Health. “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, Martinez-Gonzalez added.
“I think it’s a combination of what’s eaten and what’s not eaten,” agreed Mozaffarian, who wasn’t involved in the new research.
There were small between-group differences in some baseline characteristics in our trial, which were not clinically meaningful but were statistically significant, and we therefore adjusted for these variables. In fully adjusted analyses, we found significant results for the combined cardiovascular end point and for stroke, but not for myocardial infarction alone. This could be due to stronger effects on specific risk factors for stroke but also to a lower statistical power to identify effects on myocardial infarction. Our findings are consistent with those of prior observational studies of the cardiovascular protective effects of the Mediterranean diet, olive oil, and nuts; smaller trials assessing effects on traditional cardiovascular risk factors and novel risk factors, such as markers of oxidation, inflammation, and endothelial dysfunction; and studies of conditions associated with high cardiovascular risk - namely, the metabolic syndrome and diabetes. Thus, a causal role of the Mediterranean diet in cardiovascular prevention has high biologic plausibility. The results of our trial might explain, in part, the lower cardiovascular mortality in Mediterranean countries than in northern European countries or the United States.
The risk of stroke was reduced significantly in the two Mediterranean-diet groups. This is consistent with epidemiologic studies that showed an inverse association between the Mediterranean diet or olive-oil consumption and incident stroke.
Our results compare favorably with those of the Women’s Health Initiative Dietary Modification Trial, wherein a low-fat dietary approach resulted in no cardiovascular benefit. Salient components of the Mediterranean diet reportedly associated with better survival include moderate consumption of ethanol (mostly from wine), low consumption of meat and meat products, and high consumption of vegetables, fruits, nuts, legumes, fish, and olive oil. Perhaps there is a synergy among the nutrient-rich foods included in the Mediterranean diet that fosters favorable changes in intermediate pathways of cardiometabolic risk, such as blood lipids, insulin sensitivity, resistance to oxidation, inflammation, and vasoreactivity.
“Things that are discouraged are refined breads and sweets, sodas and red meats and processed meats,” he told Reuters Health. “The combination of more of the good things and less of the bad things is important.”
Martinez-Gonzalez suggested people seeking to improve their diet start with small changes, such as forgoing meat one or two days per 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, said Teresa Fung, a nutrition researcher at Simmons College in Boston who also wasn’t on the study team.
“All of these steps are making, at the end of the day, a big difference,” Martinez-Gonzalez said.
Fung pointed 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 told Reuters Health.
That’s likely the case for people without heart risks - including high blood pressure or cholesterol - as well, Fung added.
“This is a high-risk group, but I don’t think people should wait until they become high-risk in order to change,” she said.
SOURCE: New England Journal of Medicine, online February 25, 2013
Primary Prevention of Cardiovascular Disease with a Mediterranean Diet
Observational cohort studies and a secondary prevention trial have shown an inverse association between adherence to the Mediterranean diet and cardiovascular risk. We conducted a randomized trial of this diet pattern for the primary prevention of cardiovascular events.
Ramón Estruch, M.D., Ph.D., Emilio Ros, M.D., Ph.D., Jordi Salas-Salvadó, M.D., Ph.D., Maria-Isabel Covas, D.Pharm., Ph.D., Dolores Corella, D.Pharm., Ph.D., Fernando Arós, M.D., Ph.D., Enrique Gómez-Gracia, M.D., Ph.D., Valentina Ruiz-Gutiérrez, Ph.D., Miquel Fiol, M.D., Ph.D., José Lapetra, M.D., Ph.D., Rosa Maria Lamuela-Raventos, D.Pharm., Ph.D., Lluís Serra-Majem, M.D., Ph.D., Xavier Pintó, M.D., Ph.D., Josep Basora, M.D., Ph.D., Miguel Angel Muñoz, M.D., Ph.D., José V. Sorlí, M.D., Ph.D., José Alfredo Martínez, D.Pharm, M.D., Ph.D., and Miguel Angel Martínez-González, M.D., Ph.D. for the PREDIMED Study Investigators
February 25, 2013DOI: 10.1056/NEJMoa1200303