Food

The Mediterranean diet: what the evidence says

It is the best-tested eating pattern for the heart, and the gains are real but modest. In the PREDIMED trial, 7,447 Spanish adults aged 55 to 80 at high cardiovascular risk who were assigned a Mediterranean diet with extra-virgin olive oil or nuts had about 30 percent fewer heart attacks, strokes and cardiovascular deaths over a median of 4.8 years than a reduced-fat control group (hazard ratios 0.69 and 0.72). In a cohort of 25,315 US women followed for 24.7 years, the highest adherence went with 23 percent lower all-cause mortality, while a 2019 Cochrane review of 30 trials with 12,461 participants rated most of the evidence low to moderate quality and found no effect on death from any cause.

What the studies mean by a Mediterranean diet

Research definitions of the pattern agree on two things. The 2019 Cochrane review required both a high ratio of monounsaturated to saturated fat, in practice olive oil as the main cooking fat and often nuts, and a high intake of plant foods: fruit, vegetables and legumes. Whole grains, fish in place of meat and moderate dairy counted as additional components. The studies measure the pattern with a score.

The PREDIMED trial used a 14-item screener. In a 2012 analysis of the 7,447 trial participants (55 to 80 years old, 57 percent women), each item earned 1 point: olive oil as the main fat and at least 4 tablespoons of it a day, 2 or more servings of vegetables and 3 or more pieces of fruit a day, 3 or more weekly servings each of legumes, fish and nuts, fewer than 1 daily serving of red or processed meat and of butter or cream, fewer than 1 sweet or fizzy drink a day and fewer than 3 commercial pastries a week, poultry chosen over red meat, and a tomato, onion and garlic sauce cooked in olive oil at least twice a week. One item asks about a drink that this guide leaves out. In the same analysis, every 2 extra points went with a waist 0.92 cm smaller in women and 0.93 cm smaller in men, a cross-sectional association rather than a result of the diet. The 2024 Women's Health Study analysis used a simpler 9-point score, and its median participant scored only 4.

The one large trial and what it measured

Most of what is claimed for the diet rests on PREDIMED, a multicentre trial in Spain published in the New England Journal of Medicine in 2013 and, after a re-analysis, again in 2018. The 7,447 participants had no cardiovascular disease at entry but either had type 2 diabetes or carried 3 or more risk factors such as smoking, high blood pressure, high LDL cholesterol or a body mass index above 25. They were assigned to a Mediterranean diet plus 1 litre of free extra-virgin olive oil a week, the same diet plus free mixed nuts, or a control diet with advice to cut fat, and every group had an education session each quarter. The primary end point was a heart attack, a stroke or death from a cardiovascular cause.

After a median of 4.8 years, 288 people had suffered such an event: 96 (3.8 percent) in the olive oil group, 83 (3.4 percent) in the nut group and 109 (4.4 percent) in the control group. The adjusted hazard ratios were 0.69 (95 percent confidence interval 0.53 to 0.91) for olive oil and 0.72 (0.54 to 0.95) for nuts. In absolute terms that is roughly 1 fewer event for every 100 people over 5 years. The Cochrane review, working from the same data, graded a fall in strokes from 24 to 14 per 1,000 as moderate-quality evidence, but found little or no effect on death from any cause (hazard ratio 1.0, 0.81 to 1.24) or on cardiovascular death (0.81, 0.50 to 1.32).

The 2018 re-analysis exists because the original report was retracted: household members had been enrolled without randomisation, and at 1 of the 11 sites participants were allocated without it. The results were similar after leaving out the 1,588 participants whose assignment was in doubt, but the episode is one reason the review authors still speak of uncertainty.

What 30 trials and 25 years of follow-up add

The Cochrane review pooled 30 randomised trials with 12,461 participants from 12 countries, among them the USA, the UK, Norway, Poland, China and Brazil. For people without heart disease, the diet lowered systolic blood pressure by 2.99 mmHg (95 percent confidence interval 2.53 to 3.45) and diastolic pressure by 2.0 mmHg, moderate-quality evidence, and total cholesterol by 0.16 mmol/L, low-quality evidence. Against other diets it cut LDL cholesterol by 0.15 mmol/L and triglycerides by 0.09 mmol/L.

For people who already have heart disease the evidence is thinner. The Lyon Diet Heart Study followed 605 patients for 46 months and reported hazard ratios of 0.35 for cardiovascular death and 0.44 for death from any cause, which the review graded low quality; only 1 other trial, with 101 participants, provided usable clinical end points.

The longest view comes from the Women's Health Study, published in JAMA Network Open in 2024. Among 25,315 US women with a mean age of 54.6 at baseline, 3,879 died over a mean of 24.7 years. Compared with a score of 0 to 3 out of 9, women scoring 4 to 5 had a hazard ratio of 0.84 and women scoring 6 to 9 had 0.77, a 23 percent lower risk; cardiovascular deaths (0.83) and cancer deaths (0.80) both fell. Further adjustment for lifestyle factors shrank the ratios to 0.92 and 0.89. Blood markers explained part of the link: small-molecule metabolites 14.8 percent, inflammation markers 13.0 percent, triglyceride-rich lipoproteins 10.2 percent, body mass index 10.2 percent and insulin resistance 7.4 percent.

Where the evidence is thin

First, the trial evidence is narrow. PREDIMED enrolled older Spanish adults at high risk, and the Cochrane authors graded its mortality findings low quality and concluded that there is still some uncertainty for both primary and secondary prevention. Only 2 of the 30 trials reported on adverse events (absent or minor), and none reported on cost or quality of life.

Second, the cohort evidence is observational. The Women's Health Study measured diet once, at baseline, with a food-frequency questionnaire; height, weight and blood pressure were self-reported; and 94.9 percent of the women were White health professionals. People who score highly on a diet score also tend to smoke less and move more, which is why the hazard ratio moved from 0.77 to 0.89 once those habits were taken into account. The remaining 11 percent may still contain confounding the authors could not measure.

Third, the studies test a whole pattern, not olive oil or nuts on their own, and they compare it with a reduced-fat or usual diet. They cannot tell you whether the Mediterranean pattern beats other plant-rich patterns, or whether the benefit comes from the foods added, the foods displaced, or the attention of a dietitian every 3 months.

How to put it on your plate, and who should check first

Since 2007 NICE has advised people who have had a heart attack to eat a Mediterranean-style diet, which its 2020 guideline describes as more bread, fruit, vegetables and fish, less meat, and butter and cheese replaced by products based on plant oils. Its 2023 guideline on cardiovascular risk sets total fat at 30 percent or less of energy and saturated fat at 7 percent or less. The WHO asks for at least 400 g of fruit and vegetables and less than 5 g of salt a day, and the NHS for 2 portions of fish a week, 1 of them oily, at about 140 g each. The Plate Builder turns those targets into a plate, and the guides on 30 g of fibre a day and 30 plants a week cover the two habits the score rewards most.

A few groups should ask before changing. If you take insulin or another glucose-lowering medicine, more legumes and fruit and less refined starch can shift your glucose pattern within days, so agree the change with your diabetes team. With chronic kidney disease, the potassium in fruit, legumes and nuts and the protein in fish need a renal dietitian's limits. If you are pregnant, planning a pregnancy or breastfeeding, the NHS caps oily fish at 2 portions a week. Olive oil and nuts carry a lot of energy, so they replace butter, cream and snacks rather than joining them. Anyone with a history of disordered eating, or under 18, should treat a scoring system as information for a clinician rather than a target.

Scoring your own week

Frequently asked

Does the Mediterranean diet prevent heart attacks?

In the only large trial, 7,447 adults at high risk had about 30 percent fewer major cardiovascular events over 4.8 years, driven mainly by fewer strokes (24 down to 14 per 1,000). Deaths from any cause did not fall, and the 2019 Cochrane review graded the evidence low to moderate quality.

How much olive oil counts?

The PREDIMED score gives 1 point for olive oil as the main cooking fat and another for at least 4 tablespoons a day, used for cooking and dressing. It replaces butter, cream and margarine rather than joining them; the trial's control group was advised to reduce fat, not to avoid oil.

Do I have to eat fish?

The score rewards 3 or more servings of fish or shellfish a week, and the NHS suggests 2 portions of about 140 g, 1 of them oily. NICE does not recommend oily fish solely to prevent a second heart attack, and legumes, nuts and olive oil carry most of the pattern if you do not eat fish.

Will I lose weight on it?

Not automatically. Among the 7,447 PREDIMED participants, each 2 extra points on the 14-item score went with a waist about 0.9 cm smaller, a cross-sectional association. Olive oil and nuts are energy-dense, so the pattern works by displacing processed food, not by adding to it.

Does it work outside the Mediterranean?

The trials in the Cochrane review came from 12 countries including the USA, the UK, Norway, Poland, China and Brazil, and the 25,315 women in the Women's Health Study lived in the USA. What matters is the pattern: plant foods, olive oil in place of animal fat, fish and legumes in place of red meat.

Is it safe with diabetes or kidney disease?

Usually, but check first. Extra legumes and fruit change the glucose response for people on insulin or other glucose-lowering medicines, and the potassium in fruit, nuts and legumes needs a limit in advanced kidney disease. Ask your diabetes team or renal dietitian before changing the pattern.

Sources

• Estruch et al. 2018, NEJM: Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts (PREDIMED) · 7,447 adults aged 55 to 80, median follow-up 4.8 years, re-analysis after retraction of the 2013 report; the publisher page answers 403 to automated requests, abstract confirmed through the PubMed record 29897866
• Rees et al. 2019, Cochrane Database of Systematic Reviews: Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease · 30 randomised trials, 12,461 participants; full text on PubMed Central
• Ahmad et al. 2024, JAMA Network Open: Mediterranean diet adherence and risk of all-cause mortality in women · 25,315 women in the Women's Health Study, mean follow-up 24.7 years, 3,879 deaths; full text on PubMed Central
• Martinez-Gonzalez et al. 2012, PLoS ONE: A 14-item Mediterranean diet assessment tool and obesity indexes among high-risk subjects, the PREDIMED trial · The 14-item screener and its cut-offs, 7,447 PREDIMED participants; full text on PubMed Central
• NICE guideline NG185, 2020: Acute coronary syndromes, recommendation 1.9.1 on a Mediterranean-style diet after a heart attack · Published 18 November 2020; the diet recommendation dates from 2007 and was retained

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This guide is for general information. It does not replace medical advice or an examination.