People with heart disease have a lower risk of heart attack and strokes if they eat a Mediterranean-style diet, according to an international study of more than 15,000 people in 39 countries.

The study is the latest to extol the potential benefits of consuming fruit, vegetables, fish and unrefined foods. It found that for every 100 people with heart disease eating the highest proportion of healthy Mediterranean foods, there were three fewer heart attacks, strokes or deaths compared with 100 people eating the least amount of healthy foods during a three-and-a-half-year period.

The researchers also found that consumption of a so-called western diet - deep-fried foods, refined carbohydrates and sugary drinks – did not increase the risk of such events. They suggested that this showed eating greater amounts of healthy food was more important for people with heart disease than avoiding unhealthy foods.

Prof Ralph Stewart, from Auckland City hospital in New Zealand, who led the study, said: “The main message is that some foods – and particularly fruit and vegetables – seem to lower the risk of heart attacks and strokes, and this benefit is not explained by traditional risk factors such as good and bad cholesterol or blood pressure. If you eat more of these foods in preference to others, you may lower your risk.”

He added: “The study found no evidence of harm from modest consumption of foods such as refined carbohydrates, deep-fried foods, sugars and desserts.”

Public health guidelines already advise that a Mediterranean diet can help prevent cardiovascular disease but the authors of the paper, published on Monday in the European Heart Journal, wanted to look specifically at the effects on people who already had heart disease.

The 15,482 people in the study had an average age of 67 and were asked to fill in questionnaires on their diet. Depending on their answers, they were given a “Mediterranean diet score” (MDS), which assigned more points for increased consumption of healthy foods, with a total range of 0 to 24. A “western diet score” assigned points for increased consumption of unhealthy foods.

After adjusting for other factors that might influence the results, the researchers found that every one-unit increase in the MDS was associated with a 7% reduction in the risk of heart attacks, strokes or death from cardiovascular or other causes in patients with existing heart disease. The findings were consistent across all the geographical regions involved in the study.

As the study was observational, causal links could not be established. Other limitations included that it was based on self-reporting – with no food sample size specified – and did not examine total calorie intake nor the types of fats eaten.

Experts said it added to the body of evidence of the benefits of a Mediterranean-style diet, but they expressed reservations about the findings relating to a western diet.

Dr Tim Chico, reader in cardiovascular medicine and honorary consultant, University of Sheffield, said: “This study only examined people who already had heart disease. This is very important; most people are interested in not getting heart disease in the first place. This may explain why a ‘western’ diet did not seem to increase risk as all participants already had established heart disease. It is equally possible a western diet does increase the risk of future heart problems, but the study design was unable to detect this effect.”

Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, pointed out that the average age of participants meant they were unlikely to be heavy consumers of sugary fizzy drinks.