What the PREDIMED trial actually found
The science · 5 min read · 2026-07-09
PREDIMED randomised around 7,400 high-risk adults to a Mediterranean diet with extra virgin olive oil, the same diet with nuts, or a low-fat control. The olive oil group had roughly 30 percent fewer heart attacks, strokes and cardiovascular deaths, and the trial was stopped early.
Key points
- It was a randomised controlled trial, not a survey, which is what makes it unusually strong evidence for a diet.
- Around 7,400 participants at high cardiovascular risk, followed for about five years.
- Roughly 30 percent fewer major cardiovascular events in the olive oil group.
- The oil was extra virgin, and the effect tracked with polyphenol intake.
Nutrition research is usually observational: it watches what people eat and looks for patterns. That is why most of it is weak, and why so much of it reverses a decade later. PREDIMED is different, and it is the reason anyone can speak about olive oil and the heart with a straight face.
What they did
Spanish researchers took around 7,400 adults at high cardiovascular risk, people with diabetes or several risk factors, but no heart disease yet, and randomly assigned them to one of three diets: a Mediterranean diet supplemented with extra virgin olive oil, the same diet supplemented with mixed nuts, or a low-fat control diet. Random assignment is the crucial part. It means the groups differ by diet, not by wealth, exercise or the kind of person who chooses to eat well.
What they found
After a median of about five years, the two Mediterranean groups had roughly 30 percent fewer major cardiovascular events, heart attacks, strokes and deaths from cardiovascular causes, than the control group. The findings were published in the New England Journal of Medicine, and the trial was stopped early on the grounds that it had become difficult to justify keeping people on the control diet.
The polyphenol thread
The oil in the trial was specifically extra virgin, not refined, and follow-up analyses found that markers of polyphenol intake tracked with the benefit. That is consistent with everything else we know about how olive oil works, described in polyphenols: the whole point of olive oil, and it is why the grade and freshness of the oil is not a detail.
The honest caveats
PREDIMED was re-analysed and republished in 2018 after irregularities in how some participants were randomised at a handful of sites. The re-analysis, using more conservative methods, reached the same conclusion: the Mediterranean groups fared substantially better. It is also a trial of a whole dietary pattern in a high-risk Spanish population, not proof that any one spoonful does any one thing for any one person. What it does establish, better than any other dietary evidence we have, is that a diet built around real extra virgin olive oil protects the heart.
Common questions
What was the PREDIMED trial?
A large Spanish randomised controlled trial of about 7,400 adults at high cardiovascular risk, comparing a Mediterranean diet with extra virgin olive oil, a Mediterranean diet with nuts, and a low-fat control diet.
What did PREDIMED find about olive oil?
The group eating a Mediterranean diet rich in extra virgin olive oil had roughly 30 percent fewer major cardiovascular events, heart attacks, strokes and cardiovascular deaths, than the low-fat control group.
Is the PREDIMED trial reliable?
It was republished in 2018 after randomisation irregularities at a few sites. The more conservative re-analysis reached the same conclusion, and it remains the strongest randomised evidence for the Mediterranean diet.
How much olive oil did the PREDIMED participants use?
The olive oil group was asked to consume at least four tablespoons of extra virgin olive oil a day across their cooking and eating.
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