This article has been corrected. The original version (PDF) is appended to this article as a Supplement. The Mediterranean diet has been shown to have beneficial effects on cardiovascular risk factors. To compare the short-term effects of 2 Mediterranean diets versus those of a low-fat diet on intermediate markers of cardiovascular risk. Substudy of a multicenter, randomized, primary prevention trial of cardiovascular disease (Prevención con Dieta Mediterránea [PREDIMED] Study). Primary care centers affiliated with 10 teaching hospitals. 772 asymptomatic persons 55 to 80 years of age at high cardiovascular risk who were recruited from October 2003 to March 2004. Participants were assigned to a low-fat diet (n = 257) or to 1 of 2 Mediterranean diets. Those allocated to Mediterranean diets received nutritional education and either free virgin olive oil, 1 liter per week (n = 257), or free nuts, 30 g/d (n = 258). The authors evaluated outcome changes at 3 months. Body weight, blood pressure, lipid profile, glucose levels, and inflammatory molecules. The completion rate was 99.6%. Compared with the low-fat diet, the 2 Mediterranean diets produced beneficial changes in most outcomes. Compared with the low-fat diet, the mean changes in the Mediterranean diet with olive oil group and the Mediterranean diet with nuts group were −0.39 mmol/L (95% CI, −0.70 to − 0.07 mmol/L) and − 0.30 mmol/L (CI, −0.58 to − 0.01 mmol/L), respectively, for plasma glucose levels; −5.9 mm Hg (CI, −8.7 to −3.1 mm Hg) and − 7.1 mm Hg (CI, −10.0 to −4.1 mm Hg), respectively, for systolic blood pressure; and −0.38 (CI, −0.55 to − 0.22) and − 0.26 (CI, −0.42 to −0.10), respectively, for the cholesterol–high-density lipoprotein cholesterol ratio. The Mediterranean diet with olive oil reduced C-reactive protein levels by 0.54 mg/L (CI, 1.04 to 0.03 mg/L) compared with the low-fat diet. This short-term study did not focus on clinical outcomes. Nutritional education about low-fat diet was less intense than education about Mediterranean diets. Compared with a low-fat diet, Mediterranean diets supplemented with olive oil or nuts have beneficial effects on cardiovascular risk factors. *For a list of additional PREDIMED Study Investigators, see the Appendix.

A call for grants was issued in 2002 by the Spanish Government (Instituto de Salud Carlos III). This call was specifically designed to initiate networking research among Spanish biomedical investigators. During 2002, Ramón Estruch—the leader of our initiative—contacted different Spanish investigators (the rest of us) working in nutrition from different perspectives. We applied together for a grant to start a large randomized trial to test the effectiveness of a Mediterranean diet (MeDiet) on the ‘primary’ prevention of cardiovascular disease (CVD) and to continue the study as an observational cohort of high-risk participants to be followed-up in the long term. On 6 January 2003 our project was funded.

Adherence to the traditional Mediterranean diet (TMD) has been associated with a reduction in coronary heart disease (CHD), cancer, and overall mortality.^1-3 This protective effect has been attributed, at least in part, to the richness of this diet in antioxidants.^1,3 Current evidence indicates oxidative damage as a promoter of pathophysiological changes occurring in oxidative stress–associated diseases, such as CHD, cancer, and neurodegenerative disorders and also in aging.⁴ Oxidized low-density lipoprotein (oxLDL) level may play a major role in atherosclerosis and cardiovascular disease and is a commonly used marker for oxidative damage.^5,6 An oxLDL predictive value for the onset of mobility disability has also been recently reported.⁷ Adherence to a Mediterranean type diet has been shown to be associated with lower plasma oxLDL level in a cross-sectional study⁸ and in a linear intervention study in healthy women.⁹ However, to our knowledge, no randomized controlled intervention studies have assessed the efficacy of the Mediterranean diet on in vivo LDL oxidation.

The objective was to study oxidative status, antioxidant activities, and reactive oxygen species byproducts in whole blood and mononuclear peripherals cells and their relationship with blood pressure. Sixty-six hypertensive patients and 16 normotensive volunteers as a control group were studied. In both, whole blood and peripheral mononuclear cells oxidized/reduced glutathione ratio and malondialdehyde was significantly higher, and the activity of superoxide dismutase, catalase, and glutathione peroxidase was significantly lower in hypertensive patients when compared with normal subjects. The content of damaged base 8-oxo-2′-deoxyguanosine in nuclear and mitochondrial deoxyribonucleoproteins of hypertensive subjects was also significantly higher than that of the normotensive control subjects. No differences in these measurements were found among hypertensive subjects grouped in tertiles of 24-hour average mean blood pressure or between “white-coat” and established hypertensive subjects. Furthermore, no relationship was observed between the average of 24-hour mean blood pressure and oxidized/reduced glutathione ratio, reactive oxygen species byproducts, malondialdehide, or genomic 8-oxo-2′-deoxyguanosine. In whole blood and in mononuclear cells from hypertensive subjects, there was an increase in oxidative stress and a reduction in the activity of antioxidant mechanisms that appeared to be independent of the blood pressure values.

The PREDIMED (in Spanish: PREvención con DIeta MEDiterránea) primary prevention trial ^1–3 reported in 2013 that long-term adherence to an energy-unrestricted Mediterranean diet (MedDiet), supplemented with either extra-virgin olive oil (EVOO) or nuts, reduced cardiovascular disease (CVD). PREDIMED showed a 30% relative reduction in the composite cardiovascular primary endpoint (stroke, myocardial infarction or cardiovascular death). ^{2,, 3} However, the PREDIMED trial tested only the composition of the diet, but did not test other lifestyle interventions (i.e. energy reduction, increased physical activity (PA) and behavioural modification) frequently applied in the context of the current unprecedented obesity pandemic. ^{4,, 5} With the exception of the null results of the Look-AHEAD trial, ⁶ and the successful results of the EXERDIET-HTA study that found improvements in blood pressure, cardio-respiratory fitness and body composition (though they encouraged adherence to an hypocaloric DASH diet, instead of a Mediterranean diet), ⁷ lifestyle interventions including such components have never been tested in long-term randomized trials using hard cardiovascular events as endpoints.