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Vegan and vegetarian. Mediterranean, pescatarian and omnivore. Paleo, keto and carnivore.

Diet fads are all the rage these days with various experts emphasizing the benefits of various diets with various food items dominating each. Yet when it comes to their effects on our health and the health of our planet, not all diets are made equal.

Scientists at Tulane University who examined the nutritional quality and environmental impacts of popular diets in the United States according to a survey of 16,000 adults have found that the keto and paleo diets are the worst based both on their carbon footprints and their overall nutritional value.

“The keto diet, which prioritizes high amounts of fat and low amounts of carbs, was estimated to generate almost 3kg of carbon dioxide for every 1,000 calories consumed,” the scientists explain in a statement on their findings.

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

A vegan diet has the lowest impact on climate as it generates 0.7kg of carbon dioxide per 1,000 calories consumed, less than a quarter of emissions generated by a ketogenic diet. It is followed by the vegetarian and pescatarian diets. These findings are in line with the results of earlier research.

When it comes to nutritional quality, the pescatarian diet scored highest, followed by the vegetarian and vegan diets. The omnivore diet, which was the most common among the survey respondents, scored between the two ends of the spectum in terms of both nutritional quality and climate impacts.

“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,” says Prof. Diego Rose, the director of the nutrition program at the university’s School of Public Health and Tropical Medicine, who led the research.

If a third of all the people who follow an omnivore diet switched to a vegetarian diet for any given day, it would be equivalent to eliminating emissions that equal 340 million miles travelled by passenger vehicles, according to Rose and his colleagues.

Such reductions would matter considerably over time as a third of greenhouse gas emissions are generated by the global food system. The production of beef is especially carbon-intensive while it also drives deforestation in places like the Amazon.

Similarly, when people on omnivorous diets switched to a more plant-based Mediterranean diet or a DASH diet (the latter is low in fatty meat and is recommended for people with hypertension), both carbon footprints and nutritional quality scores improved, the experts say.

“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,” Rose says.

“Based on our results, that would reduce your footprint and be generally healthy. Our research also shows there’s a way to improve your health and footprint without giving up meat entirely,” he stresses.

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