PREDIMED Republished: Mediterranean Diet + EVOO Cut Major CV Events by 30%

This randomized controlled trial in 7,447 high-cardiovascular-risk adults in Spain, published in the New England Journal of Medicine, tested whether a Mediterranean diet supplemented with extra virgin olive oil or mixed nuts could prevent major cardiovascular events. After a median of 4.8 years, the EVOO arm showed a 31% relative reduction in heart attack, stroke, and cardiovascular death compared with a reduced-fat control diet. The 2018 NEJM paper is the republished, re-analyzed version of the original 2013 PREDIMED trial.

Why This Study Matters

PREDIMED is the largest randomized controlled trial of a dietary pattern for cardiovascular prevention ever conducted. Most diet-and-disease evidence comes from observational cohorts, which can show association but cannot prove causation. PREDIMED was a true intervention trial -- participants were randomly assigned to one of three diets, given free olive oil or nuts depending on their group, and tracked for hard cardiovascular endpoints. That design is the closest the nutrition field comes to drug-trial-quality evidence.

The 2018 republication tells the rest of the story. The trial was originally published in NEJM in 2013, but the authors later identified protocol deviations at several study sites -- some household members were enrolled without separate randomization, some participants at one site were assigned without proper randomization, and randomization tables at another site appeared to be inconsistently applied. Rather than ignore the issue, the team withdrew the 2013 paper, re-analyzed the data using statistical methods that did not depend on assuming everyone was perfectly randomized, and republished. According to PubMed, the corrected paper appeared in NEJM on June 13, 2018 (DOI: 10.1056/NEJMoa1800389).

The revised effect estimates were essentially unchanged from the 2013 numbers. The EVOO arm still showed a 31% lower risk of major cardiovascular events. The nut arm still showed a 28% reduction. That outcome is itself a strong signal -- the result survived a serious methodological audit and a re-analysis that did not rely on the perfect-randomization assumption.

How It Was Designed

The basics are in the study design bar above: 7,447 participants, three arms, median 4.8-year follow-up, multi-site trial in Spain. A few details deserve highlighting.

Participants were at high cardiovascular risk but had no diagnosed cardiovascular disease at enrollment. Inclusion required either type 2 diabetes, or at least three of the following: smoking, hypertension, elevated LDL, low HDL, overweight or obese BMI, or family history of premature coronary disease. The mean age was 67, and 57% were women. This is a primary-prevention population -- people at risk, not people who had already had an event.

The interventions were defined by what was added, not what was restricted. The EVOO arm received approximately 1 liter of extra virgin olive oil per week, free of charge, with instructions to use at least 4 tablespoons (about 50 mL) per day. The mixed-nut arm received 30 grams per day of mixed nuts (15 g walnuts, 7.5 g almonds, 7.5 g hazelnuts). The control arm received advice to reduce dietary fat and small nonfood gifts. Quarterly group sessions reinforced the dietary patterns. The use of free food provision -- not just dietary counseling -- distinguishes PREDIMED from most prior dietary trials, which depended on adherence alone.

The primary endpoint was a composite of major cardiovascular events: nonfatal myocardial infarction, nonfatal stroke, and death from cardiovascular causes. This is a hard endpoint adjudicated by a blinded outcomes committee from medical records -- not a self-reported or surrogate measure. The 2018 re-analysis used intention-to-treat with adjustment for baseline characteristics and propensity scores, and also re-ran the analysis excluding the 1,588 participants whose randomization was known or suspected to have deviated from protocol. Both analyses gave similar results.

What They Found

Compared with the reduced-fat control diet, both intervention arms reduced the risk of major cardiovascular events:

Arm	Events / N (%)	Hazard Ratio (95% CI)	Risk Reduction
Med diet + EVOO	96 / 2,543 (3.8%)	0.69 (0.53-0.91)	31% lower
Med diet + Mixed Nuts	83 / 2,454 (3.4%)	0.72 (0.54-0.95)	28% lower
Reduced-fat control	109 / 2,450 (4.4%)	1.00 (reference)	--

Green indicates a favorable direction vs. reduced-fat control. Hazard ratios are from the intention-to-treat analysis adjusting for baseline characteristics and propensity scores. Both intervention arms are statistically significant; 95% confidence intervals exclude 1.0.

Absolute event rates were 3.8% in the EVOO arm and 4.4% in the control arm over 4.8 years -- a small absolute number that compounds into substantial population-level prevention when applied at scale. The 31% relative reduction in the EVOO arm corresponds to roughly 1 to 1.5 cardiovascular events avoided per 1,000 person-years, on a baseline that includes already-elevated-risk adults.

Reading the Results

The EVOO arm and the polyphenol dose. Participants were instructed to consume at least 4 tablespoons (about 50 mL) of EVOO per day, which delivers on the order of 10 to 25 mg of olive oil polyphenols depending on the oil's phenolic concentration. A high-phenolic oil that meets the EFSA standard carries at least 5 mg of hydroxytyrosol and derivatives per 20 grams, so a 50 mL daily dose supplies well above the 5 mg/day at which the EFSA-recognized health claim on protection of blood lipids from oxidative damage applies. The mechanistic chain -- polyphenols reduce oxidized LDL, oxidized LDL drives plaque formation, plaque drives cardiovascular events -- is supported by both the EUROLIVE crossover trial (which established the lipid-oxidation mechanism in healthy adults) and PREDIMED itself, which showed the downstream hard-endpoint effect.

Comparison with the nuts arm. Both intervention arms reduced cardiovascular events to a similar degree. The interpretation in the literature is that the cardioprotective effect is driven by the Mediterranean diet pattern reinforced by either added EVOO or added nuts -- both food groups add monounsaturated fats, fiber, and plant polyphenols, which is the common biological denominator. PREDIMED does not establish EVOO as superior to nuts or vice versa for cardiovascular prevention; both significantly outperformed the reduced-fat control.

What this contributes beyond observational data. Cohort studies have consistently shown that adherence to the Mediterranean diet is associated with lower cardiovascular risk. PREDIMED's contribution is establishing that the relationship holds under randomized intervention -- when researchers assign people to the diet rather than observing who chooses it. That moves the evidence from association to support for causation.

What Didn't Change

The trial was stopped early on the basis of a prespecified interim analysis showing benefit in the intervention arms. Early stopping can overestimate effect sizes. The 2018 re-analysis addressed the randomization concerns but did not address the early-stopping concern. The effect estimates should be read as plausible but possibly modestly inflated relative to what longer follow-up might have shown.

The trial did not test isolated extra virgin olive oil against the reduced-fat diet. It tested EVOO as part of a Mediterranean diet pattern. Strictly speaking, the evidence supports the combined intervention -- not EVOO alone -- as cardioprotective. However, the polyphenol mechanism established by EUROLIVE and subsequent biomarker trials provides a coherent explanation for why the EVOO arm worked.

Broader Context

The 2011 European Food Safety Authority opinion (Regulation 432/2012) authorized a health claim for olive oil polyphenols and protection of blood lipids from oxidative damage at a daily intake of 5 mg of hydroxytyrosol and its derivatives. That claim was based primarily on the EUROLIVE trial (Covas 2006), which established the lipid-oxidation mechanism in 200 healthy European men. PREDIMED is the downstream hard-endpoint trial that complements EUROLIVE: it shows the cardiovascular event reduction at the population level that the polyphenol mechanism predicts at the cellular level.

Subsequent studies have extended PREDIMED's findings. The 2020 JACC paper from the Harvard cohorts showed 14% lower cardiovascular risk in 90,000+ U.S. adults consuming more than 0.5 tablespoons of olive oil per day. The 2022 follow-up showed 19% lower cardiovascular mortality and 29% lower neurodegenerative mortality in the same cohorts. CORDIOPREV (2022) extended the Mediterranean diet finding to secondary prevention in patients with established coronary heart disease, with the Mediterranean diet outperforming a low-fat diet over 7 years.

PREDIMED remains the foundational RCT for olive oil and cardiovascular prevention. It is cited in the U.S. Dietary Guidelines, the European Society of Cardiology guidelines, and the American Heart Association's dietary recommendations.

Related Research

Continue exploring olive oil and polyphenol science:

• Olive Oil and 19% Lower Mortality in 92,383 U.S. Adults Over 28 Years
• Olive Oil and Stroke Risk: A 101,460-Person Meta-Analysis
• Olive Oil and Brain Health: 66% Lower Cognitive Impairment Risk in PREDIMED Trial

Source: View the original study on PubMed

Olivea's Dosage

The PREDIMED EVOO arm received approximately 50 mL (about 4 tablespoons) of extra virgin olive oil per day. A single tablespoon of Olivea extra virgin olive oil delivers approximately 14 grams. Four tablespoons per day matches the PREDIMED protocol. For those seeking a concentrated polyphenol dose without the caloric load, each Olivea capsule delivers over 20 mg of hydroxytyrosol per serving in an EVOO matrix; our most recent third-party certificate of analysis confirmed 23.5 mg per capsule.

We share this research for transparency. This is an independent study -- we did not fund it, design it, or conduct it.

Editorial Information

Research note. This article summarizes third-party research published in a peer-reviewed journal. Olivea did not conduct or fund the study. Findings reflect the cited paper only and do not establish efficacy of Olivea products.

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