The so-called Mediterranean diet emphasizes olive oil, fruit, nuts, 
vegetables, and whole-grain cereals, as well as moderate intake of 
fish, poultry, and wine with meals. One of the most highly publicized 
studies of 2013 was a large trial from Spain in which 7500 adults (age 
range, 55–80) were randomized to one of three diets: a Mediterranean 
diet supplemented with extra-virgin olive oil (at least 4 tablespoons 
daily), a Mediterranean diet supplemented with walnuts, almonds, and 
hazelnuts (30 g daily), or a low-fat control diet. Although 
participants had no clinically evident cardiovascular (CV) disease, 
inclusion criteria were either diabetes or multiple nondiabetes CV 
risk factors.

During median follow-up of 5 years, rates of the primary outcome 
(myocardial infarction, stroke, or CV-related death) were 
significantly lower in both of the Mediterranean diet groups than in 
the control group. Most of the difference was attributable to lower 
stroke rates in the Mediterranean diet groups
  (NEJM JW Gen Med Mar 12 2013).

Because the low-fat control diet was not dramatically different from 
the Mediterranean diet, some observers believe that the supplemental 
olive oil and nuts were primarily responsible for this study’s 
outcome. Notably, about 50% of participants in each group were taking 
angiotensin-converting–enzyme inhibitors, 40% were taking statins, 
and 30% consumed at least one glass of wine daily. These background 
characteristics likely had some effect on the relatively low CV event 
rate in all groups.