World Vegan Day: Which diet does the most to cut your carbon footprint?

Last year, a first-of-its-kind study compared the carbon footprints of six of the most common diets.

It's well-known that around a third of greenhouse gas emissions come from the food system, and that beef production is one of the biggest culprits - emitting around 10 times more gases than chicken.

But while the environmental burden of different foodstuffs is much discussed, less research has gone into how different diets - composed of a wide variety of foods - compare.

“Climate change is arguably one of the most pressing problems of our time, and a lot of people are interested in moving to a plant-based diet," said Professor Diego Rose, senior author of the Tulane University study which also weighs up different diets’ nutritional quality.

"That would reduce your footprint and be generally healthy,” the nutrition program director at Tulane University School of Public Health and Tropical Medicine concluded. But the research also shows “there's a way to improve your health and footprint without giving up meat entirely."

Since many people will switch dietary lanes throughout their lives - or need to swerve away from veganism for health reasons - it may be reassuring to understand how our diets are a spectrum when it comes to impacting the climate.

Which diet has the biggest climate impact?

It may be unsurprising which kind of food consumption is best. A vegan diet, which means eating no food derived from animals, generates only 0.7 kg of carbon dioxide per 1,000 calories consumed.

The keto diet - a regime of high fat and low carb eating - was found to be the least sustainable, generating almost 3kg of carbon for every 1,000 calories consumed.

That’s more than four times worse than a vegan diet.

The paleo diet, which eschews grains and beans in favour of meats, nuts and vegetables, received the next lowest diet quality score and also had a high carbon footprint, at 2.6 kg of carbon dioxide per 1,000 calories.

"We suspected the negative climate impacts because they're meat-centric, but no one had really compared all these diets - as they are chosen by individuals, instead of prescribed by experts - to each other using a common framework," said Rose.

Drawing on data from more than 16,000 adult diets collected by the CDC's National Health and Nutrition Examination Survey, the study ranked vegetarian and pescatarian diets as the next best after veganism.

That leaves the omnivore diet, eating both animal and plant-based foods, which is adhered to by 86 per cent of survey participants. It sits squarely in the middle of the pack for both quality and sustainability, SciDaily reports.

And, based on the findings, if a third of those on omnivore diets began eating a vegetarian diet, on average for any given day, it would be equivalent to eliminating 340 million passenger vehicle miles.

Within omnivorous diets, the study also notes that when people refine their eating to the Mediterranean diet - which leans towards vegetables - and meat-limiting DASH diet - both carbon footprints and nutritional quality scores improve.

So even without giving up meat, there are still significant ways you can alleviate your impact on the environment.

"I think the next question is how would different policies affect outcomes and how could those move us toward healthier, more environmentally friendly diets?" said Rose.