A Mediterranean diet can lower the risk of a heart attack, stroke or early death for hundreds of millions of people who have an increased possibility of cardiovascular disease, a global review of evidence suggests.

A diet rich in olive oil, nuts, seafood, whole grains and vegetables has previously been linked to a number of benefits, and its effectiveness in helping healthy people to live longer is well known.

However, until now there has been limited evidence of how it might help those at increased risk of cardiovascular disease. These include hundreds of millions of people living with obesity, type 2 diabetes, high blood pressure or high cholesterol, and those who are physically inactive, smoke or consume harmful levels of alcohol.

Currently, guidelines recommend various diets for those at higher risk of heart issues, but they typically rely on low-certainty evidence from non-randomised studies. Now a large study – the first of its kind in the world – analysing 40 randomised controlled trials involving more than 35,000 people has provided robust evidence.

Mediterranean and low-fat diets reduce the likelihood of death and heart attack in people at heightened risk of cardiovascular disease, according to the first comparative review of seven programmes published in the BMJ journal.

“Moderate-certainty evidence shows that programmes promoting Mediterranean and low-fat diets, with or without physical activity or other interventions, reduce all-cause mortality and non-fatal myocardial infarction [heart attacks] in patients with increased cardiovascular risk,” the study’s authors wrote. “Mediterranean programmes are also likely to reduce stroke risk.”

Forty trials involving 35,548 participants – who were followed for an average of three years across seven diet programmes – were reviewed by researchers from the US, Canada, China, Spain, Colombia and Brazil.

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The seven diets were: Mediterranean, low fat, very low fat, modified fat, combined low fat and low sodium, Ornish (a vegetarian diet, low in fat and refined sugar), and Pritikin (a plant-based diet, limiting processed food).

Based on moderate-certainty evidence, Mediterranean diet programmes were better than minimal intervention at preventing all-cause mortality, non-fatal heart attack and stroke in people at risk of cardiovascular disease.

Low-fat programmes were also superior to minimal intervention, with moderate certainty, for prevention of all-cause mortality and non-fatal heart attack.

The five other dietary programmes generally had little or no benefit compared with minimal intervention, typically based on low- to moderate-certainty evidence.

The researchers acknowledged several limitations to their work, such as being unable to measure adherence to diet programmes and the possibility that some of the benefits may have been due to other elements within the programmes, such as drug treatments and support to stop smoking. Nevertheless, the BMJ said it was a comprehensive review.

“It’s long been known that eating Mediterranean-style is good for your heart, but it’s encouraging to see programmes like this lower the risk of death and heart attacks in patients already at risk of cardiovascular disease,” said Tracy Parker, a senior dietitian at the British Heart Foundation, which was not involved in the study.

“Whether you are at risk or not, a healthy lifestyle which includes a balanced diet like the Mediterranean-style diet can help you to lower your risk of developing heart and circulatory diseases,” she said. “The risk factors associated with cardiovascular disease such as type 2 diabetes, obesity, high blood pressure and high cholesterol are also reduced with a Mediterranean diet.

“It’s easy to do – make sure you are eating plenty of fruit and vegetables, beans, lentils, whole grains, fish, nuts and seeds, along with some low-fat dairy and fat from unsaturated sources like olive oil. It’s also important to eat less processed meat, salt and sweet treats.”