The results of the landmark randomized, controlled trial called PREDIMED, aimed to assess the efficacy of the Mediterranean diet in the primary prevention of cardiovascular diseases, have been published in February 25th New England Journal of Medicine. They prove that the Mediterranean diet supplemented with extra-virgin olive oil or tree nuts reduce by 30 % the risk of suffering a cardiovascular death, a myocardial infarction or a stroke. The study has been coordinated by the researcher Ramon Estruch, from the Faculty of Medicine of the UB and the Hospital Clínic, and in collaboration with professor Rosa M. Lamuela and her team from the Natural Antioxidant Research Group of the Faculty of Pharmacy.

The research is part of the project PREDIMED, a multicenter trial carried out between 2003 and 2011 to study the effects of the Mediterranean diet on the primary prevention of cardiovascular diseases.

7,447 people (age 55 to 80) with diabetes or at least three major risk factors for heart disease such as obesity, high blood pressure, elevated levels of LDL cholesterol, or a family history of early heart disease, participated in the study. They were divided into three dietary intervention groups: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with nuts (walnuts, almonds, hazelnuts), and a control group who consumed a low-fat diet that did not include olive oil or nuts. A dietician visited the patients every three months and they attended dietary training group sessions, in which they received detailed information about the Mediterranean and the low-fat diet, and the food included in each one. Moreover, they were provided with shopping lists, menus and recipes adapted to each type of diet and each season of the year.

During the study, those participants who followed any of the two types of Mediterranean diet received extra-virgin olive oil (one liter per week), and nuts (30 grams per day; 15 grams of walnuts, 7.5 grams of almonds and 7.5 grams of hazelnuts).

After five years, participants who followed any of the two types of Mediterranean diet showed a substantial reduction in the risk of suffering a cardiovascular death, a myocardial infarction or a stroke. There were 109 myocardial infarctions, strokes, or deaths from heart disease in the control group, which did not eat the Mediterranean diet. By comparison, there were 83 in the Mediterranean group that ate extra nuts, and 96 in the Mediterranean group that consumed additional olive oil.   The unadjusted hazard ratios were 0.70 (95% confidence interval [CI], 0.53 to 0.91) for a Mediterranean diet with extra-virgin olive oil and 0.70 (95% CI, 0.53 to 0.94) for a Mediterranean diet with nuts as compared with the control diet (P=0.015, by the likelihood ratio test, for the overall effect of the intervention).

The Spanish study had the collaboration of several researchers from the Hospital Clínic, the Hospital del Mar Medical Research Institute (IMIM), the faculties of Medicine of the universities Rovira i Virgili, Navarra, Valencia, Canary Islands and Malaga, as well as the University Hospital Son Espases of Palma, the Fats Institute in Seville, and the primary health care networks of Barcelona, Seville, Tarragona and Valencia.

The study was funded by the Carlos III Health Institute by means of the cooperative research thematic network (RETIC RD06/0045) and the CIBER of Physiopathology of Obesity and Nutrition (CIBERobn).