Does Diet Actually Affect Heart Disease Risk?

Direct answer: Yes, substantially, according to one of the largest dietary randomized controlled trials ever run. PREDIMED, enrolling 7,447 high-cardiovascular-risk participants, found a 30% relative risk reduction in heart attack, stroke, or cardiovascular death for people assigned to a Mediterranean diet versus a low-fat diet, an effect so strong the trial was stopped early. The trial was later retracted over a randomization error and reanalyzed; the core conclusion held.

A Trial Large and Convincing Enough to Stop Early

The PREDIMED trial randomized 7,447 participants who were free of cardiovascular disease at the start but at high risk for it, into three groups: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, and a control group counseled to follow a standard low-fat diet. The result was large enough to change the trial’s own timeline: at a median follow-up of just 4.8 years, an interim analysis found such a dramatic divergence between groups that the trial was terminated early rather than continuing to its planned endpoint. The two Mediterranean diet groups showed a 30% relative risk reduction in the trial’s primary combined outcome, heart attack, stroke, or death from cardiovascular causes, compared with the low-fat control group.

What Seems to Be Doing the Work

The research points to the Mediterranean diet’s composition itself as the likely driver: a high proportion of unsaturated fat, largely from olive oil, alongside the combined effects of other macro- and micronutrients and polyphenols from a diet built around minimally processed plant foods. The diet is notably lower in saturated fat, red meat, and dairy compared with a typical Western eating pattern, while being rich in monounsaturated fat rather than simply “low fat” across the board, an important distinction from diets that cut all fat indiscriminately.

The Honest Part Most Coverage Leaves Out: A Retraction

Here’s the detail that separates an honest account of this research from a marketing one: the original 2013 study, published in the New England Journal of Medicine, was retracted in June 2018 after researchers identified errors in the randomization procedures at some study sites. That’s a real, serious methodological problem, not a footnote to gloss over. The research team reanalyzed the data and published a corrected version, and the outcome of that honest correction is itself the most reassuring part of the story: the overall conclusion remained largely unchanged. In persons at high cardiovascular risk, major cardiovascular events were still lower among those assigned to a Mediterranean diet with olive oil or nuts than among those assigned to a reduced-fat diet, even after the randomization issues were fixed and the numbers rerun.

The Honest Takeaway for a Family

Diet’s effect on heart disease risk isn’t a soft, hard-to-pin-down claim; it’s backed by one of the largest, most rigorously scrutinized dietary trials in the field, one that survived a real retraction and reanalysis with its core finding intact. For a family with a history of heart disease or cardiovascular risk factors, the specific, evidence-backed pattern worth building toward is the one PREDIMED actually tested: minimally processed plant foods, olive oil or nuts as primary fat sources, and reduced reliance on red meat and dairy, not a vague “eat healthier” gesture but a specific dietary pattern with a real, replicated, and re-verified trial behind it.

Sources: “Mediterranean Diet and Cardiovascular Health: Teachings of the PREDIMED Study,” via PMC (pmc.ncbi.nlm.nih.gov/articles/PMC4013190) and Advances in Nutrition (advances.nutrition.org/article/S2161-8313(22)01211-X/fulltext), for the 7,447-participant trial design, the three study arms, the 30% relative risk reduction, and the early-termination-at-4.8-years finding. Harvard T.H. Chan School of Public Health, The Nutrition Source, “PREDIMED Study Retraction and Republication” (nutritionsource.hsph.harvard.edu/2018/06/22/predimed-retraction-republication), for the 2018 retraction due to randomization-procedure errors and the confirmation that the reanalyzed, corrected results left the overall conclusion unchanged. Verified Mediterranean-diet/heart-disease research against these sources on 2026-08-03.