At least a third of early deaths could be prevented if everyone became part-time vegetarians, experts say.

Harvard scientists believe a diet of eating only small amounts of meat, fish, poultry and dairy could cut people’s chance of dying early by a third.

Britain is becoming a nation of part-time vegetarians, or “flexitarians”, who have cut back on meat to be more healthy. Their numbers have increased by 2.2 million in the past two years.

Dr Walter Willett, a professor of epidemiology and nutrition at Harvard Medical School, has studied the health effects of a similar, largely plant-based, diet. Although the results are yet to be published, his preliminary analysis shows this diet slashes the danger of all early deaths.

The academic revealed the early results at the Unite to Cure Fourth International Vatican Conference in Vatican City. According to the Daily Telegraph, he said: “We have just been doing some calculations looking at the question of how much could we reduce mortality shifting towards a healthy, more plant-based diet, and our estimates are about one third of deaths could be prevented.

“That’s not even talking about physical activity or not smoking. That’s all deaths, not just cancer deaths. That’s probably an underestimate as well, as that doesn’t take into account the fact that obesity is important.

“When we start to look at it we see that healthy diet is related to a lower risk of almost everything that we look at.”

It is unclear how much meat and dairy someone would need to eat to benefit from the reduced risk.

Flexitarians eat meat occasionally, often saving it as a “treat”.