Research explained: randomized controlled trial
A Mediterranean diet with extra olive oil or nuts cut major heart events by about 30% in a large trial
What the PREDIMED trial found, why it was republished in 2018, and what it means for your shopping list.
In the PREDIMED trial, adults at high cardiovascular risk who followed a Mediterranean diet with extra-virgin olive oil or mixed nuts had roughly 30% fewer heart attacks, strokes and cardiovascular deaths than a group advised to cut fat. It remains one of the largest randomized diet trials ever run.
What the researchers did
The study enrolled 7,447 people aged 55 to 80 in Spain who did not have heart disease but had diabetes or several risk factors. They were randomly assigned to one of three diets and followed for a median of 4.8 years. Nobody was asked to cut calories.
Why was it republished?
The original 2013 paper was retracted after the authors found that randomization had not been followed at some sites, for example when members of the same household were assigned together. The team reanalyzed the data with and without those participants and published a corrected version in 2018. The main result held.
How strong is the evidence?
Good, with caveats. It was a randomized trial with hard outcomes, which is rare in nutrition. But participants were older Spanish adults at high risk, the control diet was not very different in practice, and the benefit came from the whole diet, not olive oil or nuts alone.