Abstract-A currently ongoing randomized trial has revealed that the Mediterranean diet, rich in virgin olive oil or nuts, reduces systolic blood pressure in high-risk cardiovascular patients. Here, we present a structural substudy to assess the effect of a Mediterranean-style diet supplemented with nuts or virgin olive oil on erythrocyte membrane properties in 36 hypertensive participants after 1 year of intervention. Erythrocyte membrane lipid composition, structural properties of reconstituted erythrocyte membranes, and serum concentrations of inflammatory markers are reported. After the intervention, the membrane cholesterol content decreased, whereas that of phospholipids increased in all of the dietary groups; the diminishing cholesterol:phospholipid ratio could be associated with an increase in the membrane fluidity. Moreover, reconstituted membranes from the nuts and virgin olive oil groups showed a higher propensity to form a nonlamellar inverted hexagonal phase structure that was related to an increase in phosphatidylethanolamine lipid class. These data suggest that the Mediterranean-style diet affects the lipid metabolism that is altered in hypertensive patients, influencing the structural membrane properties. The erythrocyte membrane modulation described provides insight in the structural bases underlying the beneficial effect of a Mediterranean-style diet in hypertensive subjects. Key Words: Mediterranean diet Ⅲ lipids Ⅲ membrane structure Ⅲ cardiovascular disease Ⅲ hypertension C ardiovascular disease constitutes the main cause of death in industrialized countries, 1 and hypertension is one of the main modifiable cardiovascular risk factors, especially in the elderly. 2 Healthy diet and lifestyle constitute the first steps in the guidelines for management of hypertension. 3 In this context, the type and amount of dietary lipids influence the lipid composition of cell membranes 4,5 and modulate the interactions with proteins involved in the regulation of blood pressure. 6 Thus, the changes in membrane properties induced by dietary lipids may have important consequences on the blood pressure regulation.The Mediterranean-style diet (MD) is characterized by a high consumption of virgin olive oil (VOO) and nuts, which are rich natural sources of oleic (18:1; n-9) and ␣-linolenic (18:3; n-3) acids, respectively. The Prevencion con Dieta Mediterranea (PREDIMED) Study is a large-scale, randomized trial aimed at assessing the effects of a MD enriched with VOO or nuts on primary prevention of cardiovascular disease in patients at high risk for coronary heart disease. The results of the 3-month intervention on the first 772 patients entering the study showed that, compared with a low-fat diet, the MD rich in VOO or nuts reduced systolic blood pressure and serum total cholesterol and triglyceride concentrations and increased serum high-density lipoprotein cholesterol concentration. 7 Although there is evidence indicating that dietary lipids can have a positive effect on cardiovascular risk factors, the mechani...