Study participants were enrolled between 2006 and 2010 and asked about their diet, lifestyle, medical and reproductive history, and other factors.

Responses to questions about how many raw and cooked vegetables they ate on average daily were analysed, together with their long-term health outcomes.

The researchers found the risk of dying from cardiovascular disease was about 15 per cent lower for those with the highest vegetable intake compared to the lowest.

However, this effect was substantially weakened when looking at confounders, with the effectiveness of using vegetable intake as a way to predict disease falling by 80 per cent.

‘Conclusion may not be justified’

But experts are conflicted on the findings, with some questioning the paper’s analyses.

“The conclusion drawn by the author that cooked vegetables may not be effective in reducing risk of cardiovascular disease may not be justified,” said Prof Tom Sanders, Professor Emeritus of Nutrition and Dietetics at King’s College London, who was not involved in the research.

Both independent experts and the new study’s authors stress that a good diet and maintaining a healthy weight remains important in reducing the risk of major diseases.

Co-author of the study Dr Ben Lacey, associate professor in the department at the University of Oxford, concluded: “Eating a balanced diet and maintaining a healthy weight remains an important part of maintaining good health and reducing risk of major diseases, including some cancers.

“It is widely recommended that at least five portions of a variety of fruits and vegetables should be eaten every day.”

‘Fruit and vegetables are still an essential part of a healthy diet’

Prof Naveed Sattar, professor of Metabolic Medicine at University of Glasgow, believes the recent study is not enough on its own to overturn previous findings.

“In short, this paper should in no way change the advice to eat at least five portions of fruit and vegetables a day,” he said.

“Many living in the UK fall well short of this, sadly, and more needs to be done to encourage better intake of vegetables.”

Dr Ian Johnson, a nutrition researcher and Emeritus Fellow at Quadram Institute Bioscience, who was not involved with the research, called the new study “very strong”.

“This study raises interesting questions about the relative importance of the many different aspects of healthy diet and lifestyle, but it should not discourage consumers from following public health recommendations to consume diets high in vegetables of all types,” he said.

Victoria Taylor, a senior dietitian at the British Heart Foundation (BHF), added: “Although this study found that eating more vegetables wasn’t associated with a lower risk of heart and circulatory diseases once other lifestyle and other factors were taken into account, that doesn’t mean we should stop eating vegetables.

“Fruit and vegetables remain an important source of vitamins, minerals and fibre, which make them an essential part of a healthy, balanced diet.

The findings are published in the Frontiers in Nutrition journal.