The Mediterranean diet is a pattern rather than a prescription: olive oil as the main fat, plenty of vegetables, fruit, legumes, nuts and whole grains, fish and poultry over red meat, and wine in moderation with meals. It was named for the eating habits of Crete and southern Italy in the 1960s, where heart disease was rare.

What sets it apart on this site is that it has been tested the way a drug is tested. Two large randomized trials in Spain assigned people to the diet and counted cardiovascular events for years. That is rare in nutrition and it is why this entry sits where it does on the evidence ladder.

No single ingredient explains the effect, and the trials were designed around the pattern rather than a nutrient. Olive oil polyphenols and monounsaturated fat, omega-3 from fish, fiber and polyphenols from plants, and nuts each have trial support for lowering blood pressure, improving lipids and endothelial function, and reducing inflammation. The pattern also displaces processed food, refined carbohydrate and red meat. Which of those does the work is unresolved, and the trials suggest it does not need to be resolved for the pattern to help.

Primary prevention: PREDIMED. The trial assigned 7,447 Spaniards aged 55 to 80 at high cardiovascular risk but without cardiovascular disease to a Mediterranean diet with extra-virgin olive oil, the same diet with nuts, or advice to reduce fat. After a median of 4.8 years, major cardiovascular events were 31% lower with olive oil and 28% lower with nuts. The 2013 paper was withdrawn after randomization problems at some sites were found, and republished in 2018 with analyses that do not rely on everyone having been randomized; the result held.

A pre-specified PREDIMED substudy in 447 cognitively healthy participants found both Mediterranean arms scored better than control on memory and executive composites after a median of four years, while the control group declined.

Secondary prevention: CORDIOPREV. In 1,002 patients with established coronary disease, a Mediterranean diet versus a low-fat diet over seven years reduced major cardiovascular events, with hazard ratios around 0.72 to 0.75. The effect was clear in men and not detectable in the 175 women.

Cohorts. A 2008 meta-analysis of twelve prospective studies in over 1.5 million people found that each two-point increase in a Mediterranean adherence score was associated with 9% lower overall and cardiovascular mortality, 6% lower cancer incidence or mortality, and 13% lower incidence of Parkinson's and Alzheimer's disease.

The diet is food, and the trials reported no harms from it. The caution is the wine component: the trials allowed moderate wine with meals in people who already drank, and the epidemiology of moderate alcohol has weakened considerably since; nothing in the diet depends on it. Nut allergy rules out that arm. Olive oil is calorie-dense, and the PREDIMED arms did not gain weight, but the diet was not designed for weight loss.

Not a product. Most national dietary guidelines now describe a Mediterranean-style pattern as one of their recommended patterns, and cardiology societies in Europe and the United States cite PREDIMED in their prevention guidelines. The one regulatory footnote is the PREDIMED retraction and republication, a transparency event that strengthened rather than weakened the evidence.