"Plant-based" is a real buzzword in nutrition right now. On Instagram #plantbased yields over 15 million posts.

Plants are popular, it seems, at least in the world of social media.

It is also a term which often pops up in health research. One recent headline caught my eye: "A THIRD of premature deaths could be avoided if we all cut out meat, Harvard study finds."

That's a dramatic claim. But is it true? And what does plant-based even mean?

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It seems there is no official definition; despite the impression we may get from Instagram and newspaper headlines. Vegetarians and vegans have claimed the term, which means many of us now believe plant-based equals nothing but quinoa bowls and nut milk.

But others - including the Harvard professor to whom the recent claims about premature deaths were attributed - use a more literal translation. To them, plant-based means just that: a varied diet based on plants.

The Harvard study was not a new piece of research. Rather, it was the quoted comments from Professor Walter Willett, an epidemiologist at Harvard University's TH Chan School of Public Health.

He was speaking at a public health conference, where he didn't actually say we'd all be better off giving up meat. 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, not necessarily totally vegan, and our estimates are about one-third of deaths could be prevented."

Willetts' calculations were based, he later said, on multiple studies he has been involved with, as well as a substantial body of evidence. The general conclusion of that evidence is that more plant food is generally beneficial.

As humans, though, we tend to want more detail. "Yes, but which diet should I follow?" we might legitimately ask.

A 2014 review published in the Annual Review of Public Health, titled "Can We Say What Diet is Best for Health?" attempted to seriously answer this question.

The researchers looked at seven popular diets, including the low-carb; vegetarian/vegan; paleo and Mediterranean diets. They concluded the answer to the question of the title is no: there is no one diet that comes out as "best".

But they also concluded that all of the diets surveyed contained good and healthful elements, and that the things they had in common pointed to a healthy pattern of eating which, they say, is likely to lead to better health and a longer life.

Those common elements were: limited refined starches, added sugars and processed foods, a limited intake of certain fats, and an emphasis on whole plant foods, with or without lean meats, poultry, fish and seafood.

There's a wealth of evidence, the researchers said, that this pattern of eating (note the term pattern, not "diet" in the sense of a restrictive eating regimen), is health-promoting.

To eat mostly plants, we may need to re-think how we put our meals together. Many of us are in the habit of basing our meals on a protein - often meat - and adding vegetables and starches around that. It can be useful to flip that thinking.

Meat is not outlawed, but think of it as a garnish, not the main event. This will almost guarantee you'll eat more plants and less animal products.

It's important to note that no matter what variation of "plant-based" diet you choose - vegetarian, vegan or including animal products - the quality of what you're eating makes a huge difference.

It is entirely possible, experts say, to eat a very unhealthy vegetarian or vegan diet, just as it is possible to be an unhealthy meat-eater.

Niki Bezzant is editor-at-large for Healthy Food Guide.