Up to a third of early deaths could be prevented if we all switched to a vegetarian diet, according to new calculations by Harvard Medical School scientists.

While we already know about many of the benefits of not eating meat, this latest figure is much higher than previous estimates.

The researchers presented the figures at the Unite to Cure Fourth International Vatican Conference in Vatican City last week. 

The work is yet to be published in a peer reviewed journal, so we need to be skeptical about these numbers for now. But such bold claims are worth further investigation.

Estimates vary between countries but roughly 30 million deaths every year across the globe are classed as "preventable" – those caused by things we can arguably do something about, such as obesity, smoking, poor diet, and so on.

Cutting those numbers down by a third would be a massive achievement.

And according to researchers from Harvard Medical School, switching to a plant-based diet could play a bigger part in that than previously realised. 

"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, not necessarily totally vegan, and our estimates are about one third of deaths could be prevented," said one of the team, Walter Willett, as reported by The Telegraph.

"That's not even talking about physical activity or not smoking, and 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 and we control for obesity."

As we mentioned earlier, we haven't seen a paper on this yet, and other scientists have yet to analyse the figures produced by Willett and his colleagues.

Even so, other attendees at the conference agreed that a vegetarian diet could do more for stopping preventable deaths than previous studies suggested.

In short, a healthier diet has a knock-on effect on almost every other aspect of the body's health.

David Jenkins, from the University of Toronto in Canada, was also at the Unite to Cure event and presented research looking at lowland gorilla diets – rich in stems, leaves, vines and fruit.

When the same diet was recreated for humans, it led to a 35 percent fall in their cholesterol in just two weeks.

So what is it that makes these diets so good for us?

The nutrients in a properly managed vegetarian diet are known to lower blood pressure, reduce the risk of a heart attack, and lower body mass index (BMI).

At the same time, studies have shown that eating certain red meats increases your risk of cancer.

Add to that the environmental benefit of not having livestock to look after and manage, and the benefits of a meat-free diet quickly begin to stack up.

At the same time, vegetarians also need to be careful about what they eat – particularly in making sure they get the protein, calcium, iron, and vitamin B12 typically provided by meats. So it's definitely not a case of one diet being perfect for all humans.

What this latest research suggests is that cutting back on meat could be better for us than we ever realised – at least in terms of avoiding an early death. And that could help inform all of our diets, whether we completely give up meat or not.

"I think people imagine that a healthy diet has only a modest effect and a vegetarian diet might help you lose a little bit of weight," Neal Barnard, president of the Physicians Committee for Responsible Medicine, told the conference, as The Telegraph reports.

"But when these diets are properly constructed I think they are enormously powerful."