Barcelona, Spain - Once again, Mediterranean-style diets rich in olive oil or nuts have proved to have more beneficial effects on cardiovascular risk factors than a conventional low-fat diet [1]. The findings, this time from the Prevención con Dieta Mediterránea (PREDIMED) study, should help allay fears about fat—at least good fat—in people who are overweight and have other cardiovascular risk factors, authors of the study say.

"When nutritional advice is given to people with increased adiposity, reluctance still exists to recommend high-fat, high-monounsaturated fatty-acid diets as an alternative to the traditional—and less palatable—low-fat diets, in the belief that fat provides excess energy, thus promoting obesity," lead author on the study, Dr Ramon Estruch (Hospital Clinic, Villarroel, Barcelona, Spain), commented to heartwire. "Despite the fact that many participants in the current study were obese, those allocated to the Mediterranean diet groups slightly reduced body weight and adiposity measures. Thus, our results are reassuring with respect to the lack of weight gain when supplementing ad libitum diets with sizable amounts of unsaturated fats, such as those contained in olive oil or nuts. Our results also add to the increasing evidence that diets enriched with nuts do not induce weight gain."

To explore the value of foods high in monounsaturated fats and antioxidants, Estruch and colleagues randomized 772 asymptomatic patients with either type 2 diabetes or three or more CHD risk factors to a low-fat diet or to a Mediterranean-type diet supplemented with either olive oil (1 L per week) or tree nuts (30 g per day). Subjects in all three groups were advised to increase intake of vegetables, legumes, fruit, and fish, while decreasing their intake of meat, sugary foods, and dairy.

After three months, weight and body-mass index (BMI) were slightly reduced in all three groups, with no differences between groups. Participants in the two Mediterranean-diet groups, however, had lower mean plasma glucose levels, lower systolic blood pressure, and lower total-cholesterol/HDL-cholesterol ratios than those in the low-fat-diet group. Markers of inflammation were also slightly lower in the subjects eating the Mediterranean diets. The two Mediterranean diets were also associated with lower fasting glucose levels in all subjects randomized to these diets and lower fasting insulin levels and insulin resistance in nondiabetic subjects.

To heartwire, Estruch acknowledged that the time line of the trial reported to date is too short to appreciate lasting effects of the diets or their impact on clinical outcomes, but he emphasizes the effects on CV risk factors as intermediate markers point "in the right direction."

"This feeding trial confirms that an intervention with a Mediterranean-style diet has better healthy effects on cardiovascular risk factors than the so-called 'low-fat diet,' " he commented. "In the era of evidence-based medicine, nutritional recommendations should be based on large-scale randomized intervention studies in which clinically relevant end points are evaluated."

To this end, the PREDIMED investigators are also assessing the effects of the two Mediterranean diets on all-cause mortality and on the incidence of heart failure, diabetes, and cancer.

"Longer follow-up of the whole PREDIMED trial will eventually provide stronger evidence," he stated. "In the meantime, an increasing body of knowledge supports the Mediterranean-style diet as a useful tool in the management of individuals at high risk for cardiovascular heart disease."