Mediterranean Diet and Heart Health: What PREDIMED and the Other Trials Show
The link between the Mediterranean diet and heart health is one of the most quoted ideas in nutrition — and one of the least often explained. Most pages tell you the diet is "good for your heart" and move straight on to a shopping list. This article does the part they skip: it walks through the actual randomised trials, one by one — the Lyon Diet Heart Study, PREDIMED (including why its first report was retracted), CORDIOPREV — and the Cochrane review that weighed them. You will see who was studied, what they ate, what was measured, how big the differences were, and where the evidence is still thin. We sell extra virgin olive oil, so we will also be plain about what these trials do and do not say about olive oil itself, and about when to talk to a clinician before you change how you eat.
For our own oil, see our Cold-Pressed Single-Estate Extra Virgin Olive Oil - Marrakech (500ml).
The Short Answer
- Three randomised trials have tested a Mediterranean-style diet against a comparison diet and measured hard heart outcomes: the Lyon Diet Heart Study (605 people after a first heart attack), PREDIMED (7,447 people at high cardiovascular risk) and CORDIOPREV (1,002 people with established coronary heart disease).
- All three reported fewer major cardiovascular events in the Mediterranean-diet group, but each has limits: Lyon was small and used a rapeseed (canola) margarine, PREDIMED had its 2013 report retracted and republished in 2018, and CORDIOPREV was a single-centre trial whose benefit showed in men but not in its 175 women.
- In PREDIMED's corrected 2018 analysis (Estruch et al., New England Journal of Medicine), the group given a Mediterranean diet plus extra virgin olive oil had a hazard ratio of 0.69 for major cardiovascular events compared with a reduced-fat control diet.
- A 2019 Cochrane review (Rees et al.) judged much of this evidence low to moderate quality and concluded that some uncertainty remains, especially for people who already have heart disease.
- What was tested was a whole eating pattern — vegetables, pulses, wholegrains, fish, nuts and olive oil together — not olive oil on its own, and none of it replaces prescribed treatment.
- Sidr & Stone's extra virgin olive oil is single-estate and cold-pressed within hours of harvest on our own farm outside Marrakech: a good fat for this way of eating, and a food, not a medicine.
Is the Mediterranean Diet Good for Your Heart?
On the trial evidence, a Mediterranean-style diet is linked with fewer heart attacks, strokes and cardiovascular deaths than the comparison diets it was tested against, in both people at high risk and people with existing heart disease. The evidence is stronger than for most diets, but Cochrane reviewers still rate it low to moderate quality.
That answer has two halves, and both matter. The first half is why cardiologists and heart charities recommend the pattern: few eating patterns have been tested in randomised trials with heart attacks and deaths as the outcome, rather than cholesterol numbers alone. The second half is why careful writers hedge: those trials are few, each has a design weakness, and the comparison diets differed from trial to trial. A "low-fat diet" in one study and a "usual post-heart-attack diet" in another are not the same yardstick.
It also helps to be clear about the words. In these trials, "Mediterranean diet" means a pattern rich in vegetables, fruit, pulses, wholegrains, nuts and fish, with olive oil as the main added fat and less red and processed meat. If you want to see what that looks like across a week, our 7-day Mediterranean diet meal plan sets it out meal by meal.
The Trials at a Glance
Here are the three outcome trials and the main review side by side. Each figure below comes from the published abstract, checked against Europe PMC for this article.
| Study | Who took part | Compared with | Main finding | Key limitation |
|---|---|---|---|---|
| Lyon Diet Heart Study (de Lorgeril et al., Lancet 1994; Circulation 1999) | 605 people after a first heart attack, France | Usual "prudent" post-heart-attack diet | Cardiac death or non-fatal heart attack: 14 events vs 44 over a mean of 46 months | Small; an alpha-linolenic acid-rich diet with a supplied rapeseed (canola) margarine, not mainly olive oil |
| PREDIMED (Estruch et al., NEJM 2018, corrected and republished) | 7,447 adults aged 55–80 at high cardiovascular risk, no heart disease at entry, Spain | Advice to reduce dietary fat | Major cardiovascular events: 3.8% (olive oil arm) and 3.4% (nuts arm) vs 4.4%; HR 0.69 and 0.72 | 2013 report retracted over randomisation problems; reanalysed in 2018 |
| CORDIOPREV (Delgado-Lista et al., Lancet 2022) | 1,002 people with coronary heart disease, aged 20–75, Córdoba, Spain | Low-fat diet | Major cardiovascular events: 87 vs 111 over 7 years; adjusted HR about 0.72–0.75 | Single centre; 82.5% men; no difference seen in women |
| Cochrane review (Rees et al., 2019) | 30 randomised trials, 12,461 participants | Various control diets | Some benefits, especially on stroke in PREDIMED and on blood pressure | Evidence mostly low to moderate quality; "some uncertainty" remains |
Read across the rows and a pattern appears: the direction of the effect is consistent, but no single trial is clean enough to carry the whole case alone. That is exactly why each one deserves a closer look.
The Lyon Diet Heart Study: Where the Trial Evidence Began
The Lyon Diet Heart Study was the first randomised trial to test a Mediterranean-type diet against hard heart outcomes. Researchers in France recruited people who had just had a first heart attack and randomly assigned 302 to a Mediterranean-style diet and 303 to the usual cautious diet advised after a heart attack at the time.
The intermediate results, published in The Lancet in 1994 by de Lorgeril and colleagues, were striking. After a mean of 27 months there were 3 cardiac deaths in the Mediterranean group against 16 in the control group, and 5 non-fatal heart attacks against 17 — an adjusted risk ratio of 0.27 for those two outcomes combined. The extended follow-up in Circulation in 1999, with a mean of 46 months per patient, reported 14 such events against 44.
Two details are often left out. First, the trial was small: a few dozen events decide the result, so the effect size is uncertain even though it is large. Second, the experimental diet was described as "alpha-linolenic acid-rich", and the Cochrane reviewers note that participants were given a rapeseed (canola) margarine. So the Lyon trial supports the Mediterranean pattern as a whole — it is not a trial of olive oil.
The 1999 report also made a point that still matters for anyone reading about diet and the heart: high cholesterol and high blood pressure remained independent predictors of further events in both groups. In the authors' words, the diet "did not alter" the usual relationship between those risk factors and recurrence. Diet worked alongside the standard risk factors, not instead of managing them.
PREDIMED: The Big Trial, Its Retraction and Its Republication
PREDIMED is the trial most people mean when they say "the science shows". It enrolled 7,447 people in Spain aged 55 to 80, 57% of them women, who did not have cardiovascular disease but were at high risk of it. They were randomly assigned to one of three diets: a Mediterranean diet supplemented with extra virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet with advice to reduce dietary fat. Participants received regular education sessions and, depending on their group, free extra virgin olive oil, free nuts or small non-food gifts.
After a median of 4.8 years, a major cardiovascular event — heart attack, stroke or death from cardiovascular causes — had occurred in 96 people (3.8%) in the olive oil group, 83 (3.4%) in the nuts group and 109 (4.4%) in the control group. In the corrected analysis published by Estruch and colleagues in the New England Journal of Medicine in 2018, the hazard ratio was 0.69 for the olive oil group and 0.72 for the nuts group, compared with the control diet.
Why the 2013 paper was retracted
The trial's results were first published in the same journal in 2013. Afterwards, the investigators identified protocol deviations: some household members of participants had been enrolled into the same group without being randomised; at one of the eleven sites, some participants were assigned to a group without randomisation; and at another site, randomisation tables appear to have been used inconsistently. Because a randomised trial's strength depends on randomisation, the 2013 paper was withdrawn and a new report published in 2018.
The 2018 version did not simply repeat the old numbers. It reported effect estimates from analyses that did not assume every participant had been properly randomised, and it repeated the main analysis after leaving out the 1,588 participants whose group assignment was known or suspected to have departed from the protocol. The results were similar. So the honest summary is neither "PREDIMED was debunked" nor "the retraction did not matter": the trial was flawed, the flaw was disclosed and analysed, and the corrected result pointed the same way.
What PREDIMED does and does not tell you
Even corrected, PREDIMED has limits worth knowing. The absolute difference was modest — fewer than one event per 100 people over almost five years (3.8% against 4.4% in the olive oil comparison). The control group was given advice to cut fat rather than a carefully matched diet. And when the Cochrane reviewers looked at single outcomes, the clearest effect in PREDIMED was on stroke (hazard ratio 0.60, moderate-quality evidence), while the effect on cardiovascular death alone was uncertain (hazard ratio 0.81, with a confidence interval running from 0.50 to 1.32).
CORDIOPREV: Testing the Diet in People Who Already Have Heart Disease
PREDIMED studied people without heart disease. CORDIOPREV asked the follow-up question: does a Mediterranean diet beat a low-fat diet in people who already have coronary heart disease? The trial, reported by Delgado-Lista and colleagues in The Lancet in 2022, randomly assigned 1,002 patients aged 20 to 75 at the Reina Sofia University Hospital in Córdoba, Spain, and followed them for seven years with dietitian support.
The primary outcome — a composite of heart attack, revascularisation, ischaemic stroke, peripheral artery disease and cardiovascular death — occurred in 87 people on the Mediterranean diet and 111 on the low-fat diet. Adjusted hazard ratios ranged from about 0.72 to 0.75 in favour of the Mediterranean diet.
The limits are just as clear. CORDIOPREV was a single-centre trial, so its results may not travel perfectly to other countries and health systems. Participants knew which diet they were on, although the clinicians judging outcomes did not. And 82.5% of participants were men: the benefit was clearer in men, and among the 175 women the researchers found no difference between the diets. The trial also listed funding from olive oil sector foundations alongside Spanish government and European Union sources — the paper discloses this, and readers are entitled to weigh it.
What the Cochrane Review Concluded
Cochrane reviews exist to weigh every eligible trial, not just the famous ones. The 2019 update by Rees and colleagues, "Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease", included 30 randomised trials with 12,461 participants. It was published before CORDIOPREV, so that trial is not in it.
For people without heart disease, the reviewers found moderate-quality evidence of small falls in blood pressure (about 3 mmHg systolic and 2 mmHg diastolic) and low-quality evidence of a possible small fall in total cholesterol. For people with heart disease, they described "a paucity of evidence", with the Lyon trial the main contributor. Their overall conclusion was that, despite the number of studies, "there is still some uncertainty" about the diet's effects on clinical outcomes and risk factors.
That is not a verdict against the Mediterranean diet. It is a statement about how strong the evidence is, and it is the right frame for anyone tempted to treat a diet as a treatment. For the narrower questions that sit inside this one, we have separate guides to olive oil and cholesterol and olive oil and blood pressure.
Where Olive Oil Fits — and Where It Does Not
Because we sell olive oil, this is the section to read most sceptically. Of the three outcome trials, only PREDIMED had an arm built around extra virgin olive oil, and its nuts arm did about as well. Lyon leaned on a rapeseed-based margarine. CORDIOPREV tested a Mediterranean diet that includes olive oil, against a low-fat diet. None of them tested olive oil on its own, so none of them shows that adding a spoonful of oil to an otherwise unchanged diet protects the heart.
What the evidence does support is olive oil's role as the main added fat in a wider pattern — used in place of butter, lard and other saturated fats, not on top of them. The list of permitted health claims in Regulation (EU) No 432/2012, which also applies in the UK as assimilated law, reflects that. For oleic acid, the main fat in olive oil, the authorised wording is: "Replacing saturated fats in the diet with unsaturated fats contributes to the maintenance of normal blood cholesterol levels. Oleic acid is an unsaturated fat." That claim may only be used for foods high in unsaturated fat.
For olive oil polyphenols, the authorised wording is: "Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress." That claim may only be used for olive oil containing at least 5 mg of hydroxytyrosol and its derivatives per 20 g, with the information that the effect is obtained with a daily intake of 20 g. We have not yet published a polyphenol test for our own oil, so we do not make that claim for it. Our guide to olive oil polyphenols explains what the figures mean, and our wider piece on olive oil and heart health covers the oil-specific research.
Before You Change Your Diet: When to Talk to a Clinician
For most healthy adults, eating more vegetables, pulses, fish and nuts, and cooking with olive oil instead of butter, is low-risk. But some people should check with a professional first, and nobody should treat a diet as a replacement for prescribed care.
- If you take medicines for blood pressure, cholesterol, diabetes or your heart, keep taking them as prescribed. In the trials above, diet was studied alongside standard care, not instead of it. Tell your GP or pharmacist about big changes to how you eat.
- If you take warfarin, the NHS advises talking to your doctor before making big changes to your diet: foods high in vitamin K, such as broccoli, spinach and other green leafy vegetables, can affect how warfarin works. You can still eat them — ask your warfarin clinic how.
- If you have had a heart attack, stroke or heart surgery, ask your cardiology or cardiac rehabilitation team, or a registered dietitian, to help you adapt the pattern. CORDIOPREV used dietitians for exactly this reason.
- If you have kidney disease, diabetes, food allergies, or are pregnant, get individual advice on portions, nuts and fish choices.
- On wine: many popular guides mention it. Nothing in this article is a reason to start drinking alcohol; if you drink, discuss safe limits with your GP.
New or worsening chest pain, breathlessness or other heart symptoms need medical assessment, not a change of diet. In an emergency, call 999 in the UK, 112 or 999 in Ireland, or 911 in the US.
When you do bring olive oil into the kitchen, quality matters for taste and for the compounds the research is interested in. Our guide to choosing a quality olive oil covers grade, harvest date, storage and labels, and our Mediterranean diet shopping list covers the rest of the basket.
Why Sidr & Stone
The trials above are about an eating pattern in which extra virgin olive oil is the everyday fat. We make one oil, carefully, for that everyday role — and we would rather you understood the evidence than took our word for it.
- Single-estate — our own family-owned farm on the plains outside Marrakech, Morocco; we control every step from tree to bottle, with no blending across origins.
- Rain-fed — no irrigation; the trees take what the season gives.
- Organically grown — no synthetic fertilisers, pesticides or herbicides (not yet certified; certification is in progress).
- Single harvest — a small, limited batch; once the current batch is gone, it is gone until the next.
- Cold-pressed within hours of harvest — to keep flavour, aroma and polyphenols.
- Unfiltered extra virgin — minimally processed; natural sediment is normal.
- 100% natural — a single ingredient, olive oil, with nothing added.
- Dark glass with a gold label — protection against the light that degrades oil.
- 10% of profits to charity, across everything we sell.
- Fulfilment in the UK, EU and US.
We will not tell you our oil protects your heart — no trial has tested it, and that would be exactly the kind of claim this article warns against. What we will say is that it is single-estate Moroccan extra virgin olive oil, rain-fed, organically grown and cold-pressed within hours of harvest: a good fat to build a Mediterranean-style kitchen around.
Frequently Asked Questions
What does the research say about the Mediterranean diet and heart health?
Three randomised trials — Lyon, PREDIMED and CORDIOPREV — reported fewer major cardiovascular events with a Mediterranean-style diet than with the comparison diet. A 2019 Cochrane review rated the evidence mostly low to moderate quality and concluded that some uncertainty remains, particularly for people who already have heart disease.
Why was the PREDIMED study retracted?
The 2013 report was withdrawn after the investigators found protocol deviations: some household members were enrolled without randomisation, some participants at one of eleven sites were assigned without randomisation, and randomisation tables appear to have been used inconsistently at another. The trial was reanalysed and republished in 2018, with similar results.
Is the Mediterranean diet good for high cholesterol or high blood pressure?
The Cochrane review found moderate-quality evidence of small reductions in blood pressure and low-quality evidence of a possible small fall in total cholesterol in people without heart disease. If you have high cholesterol or blood pressure, the diet can sit alongside your treatment plan — agree any changes with your GP rather than replacing medicines.
Is the Mediterranean diet suitable after a heart attack or stroke?
The Lyon and CORDIOPREV trials both studied people with existing heart disease and reported fewer further events, but Cochrane describes this evidence as limited. Ask your cardiac rehabilitation team or a registered dietitian to tailor the pattern to your condition and medicines.
Is it the olive oil or the whole diet that matters?
The trials tested whole diets. In PREDIMED, the extra virgin olive oil and nuts arms had similar results, and the Lyon diet used a rapeseed-based margarine. Olive oil is best seen as the main fat within the pattern, used in place of saturated fats, not as a stand-alone remedy.
How is Sidr & Stone's oil different from a supermarket olive oil?
It comes from one farm we own outside Marrakech, is rain-fed and organically grown (not yet certified), and is cold-pressed within hours of harvest and left unfiltered. We have not published polyphenol test results yet, so we do not claim specific figures for it.
Where can I buy Sidr & Stone extra virgin olive oil?
Directly from our product page, where it is available to pre-order as a limited single-harvest batch, with fulfilment in the UK, EU and US.
Is olive oil a medicine?
No. Olive oil is a food, not a medicine. It has a long traditional history — including being honoured in the Prophetic Sunnah — and a substantial body of modern research, particularly around polyphenols, cardiovascular health, and the Mediterranean diet pattern. It can be a worthwhile part of a healthy routine, but it does not cure diseases and is not a substitute for medical care. Be cautious of any olive oil marketed with specific disease-cure claims.
Final Thoughts
The Mediterranean diet's reputation for heart health rests on more than enthusiasm: three randomised trials, in different kinds of patients, all pointed the same way. It also rests on fewer trials than its fame suggests, one of which had to be retracted and corrected, and a Cochrane review that still calls the picture uncertain. Both things are true, and holding them together is what makes the evidence useful rather than a slogan.
The practical message is simple. Eat more vegetables, pulses, wholegrains, nuts and fish; let extra virgin olive oil replace the saturated fats; keep your clinician in the loop and your medicines as prescribed.
Our Cold-Pressed Single-Estate Extra Virgin Olive Oil - Marrakech (500ml) — single-estate, rain-fed and pressed within hours of harvest — is available to pre-order now as a limited single-harvest batch, with fulfilment in the UK, EU and US.
Our extra virgin olive oil is grown organically on our own single-estate farm on the plains outside Marrakech: we control every step from tree to bottle, and no synthetic pesticides, herbicides or fertilisers are used. It is not yet certified organic — certification is in progress, and we will publish it as soon as it comes through.
References
- de Lorgeril M, Renaud S, Mamelle N, et al. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. Lancet. 1994;343(8911):1454-1459. PMID 7911176. doi:10.1016/S0140-6736(94)92580-1
- de Lorgeril M, Salen P, Martin JL, et al. Mediterranean diet, traditional risk factors, and the rate of cardiovascular complications after myocardial infarction: final report of the Lyon Diet Heart Study. Circulation. 1999;99(6):779-785. PMID 9989963. doi:10.1161/01.CIR.99.6.779
- Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013;368(14):1279-1290. PMID 23432189. doi:10.1056/NEJMoa1200303. Retracted — replaced by reference 4.
- Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. N Engl J Med. 2018;378(25):e34. PMID 29897866. doi:10.1056/NEJMoa1800389
- Delgado-Lista J, Alcala-Diaz JF, Torres-Peña JD, et al. Long-term secondary prevention of cardiovascular disease with a Mediterranean diet and a low-fat diet (CORDIOPREV): a randomised controlled trial. Lancet. 2022;399(10338):1876-1885. PMID 35525255. doi:10.1016/S0140-6736(22)00122-2
- Rees K, Takeda A, Martin N, et al. Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2019;3:CD009825. PMID 30864165. doi:10.1002/14651858.CD009825.pub3
Disclaimer: This article summarises published research and regulatory wording on the Mediterranean diet and cardiovascular health at the time of writing; research findings and guidance may change, and readers should check current sources. It is not personal medical or dietary advice. Olive oil is a food, not a medicine, and is not a substitute for medical treatment of any condition. If you have a medical condition, take regular medicines or are pregnant, speak to your GP, a registered dietitian or your pharmacist before changing your diet. For any health concern, consult a qualified medical professional.