The study, conducted by the University of Oxford, analysed data from more than 48,000 adults who signed up to a wider study between 1993 and 2001, and who had no history of heart disease or stroke.
The participants were asked questions on lifestyle, medical history and diet, allowing the team to classify individuals as meat-eaters (24,428 people), vegetarians and vegans (16,254 people) or pescatarians (7,506 people).
Some of these questions were asked again in 2010 and participants were re-classified if they had switched diet.
The health of participants was followed through medical records until March 2016, during which time there were 2,820 cases of coronary heart disease and 1,072 cases of stroke.
After adjusting for factors that might influence the results, including age, sex, smoking status and socioeconomic status, researchers found that fish eaters had a 13 per cent reduced risk of heart disease than meat eaters, while vegetarians and vegans had a 22 per cent lower risk.
Meanwhile, vegetarians had a 20 per cent higher risk of having a stroke than meat-eaters. There was no clear effect for fish-eaters.
Overall, the findings showed that over a 10-year period, there would be 10 fewer cases of coronary heart disease in vegans and vegetarians than in meat eaters per 1,000 people, but three more cases of stroke.
The team said the increased risk of stroke could be down to lower levels of vitamins among the vegetarians and vegans in the study.
“We observed lower rates of ischaemic heart disease in fish eaters and vegetarians than in meat eaters, which appears to be at least partly due to lower body mass index and lower rates of high blood pressure, high blood cholesterol, diabetes associated with these diets,” the researchers explained.
The team acknowledged that the study, which was published in the British Medical Journal, had limitations, including the fact that it is based on self-reporting and mainly involved white people living in the UK.
Tracy Parker, senior dietitian at the British Heart Foundation, said: ”This study provides further evidence that eating more plant-based foods can help lower our risk of heart disease.
“However, it also found that vegetarians, including vegans, are at a higher risk of stroke than meat eaters - potentially due to lack of certain nutrients.
"Whilst this is an interesting finding, this study is observational and doesn't provide us with enough evidence, so more research in this area would be needed.”
Parker explained that one way people can reduce their risk of heart and circulatory diseases is to ensure they are eating a balanced diet, packed with plenty of fruit and vegetables, wholegrains, beans, lentils, nuts and seeds.
“For those who do eat meat, cutting back to less than 90g of red or processed meat a day is advised,” she added.
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