Scientists rate the healthiest diets for you and the planet

DDiscussions about the benefits and pitfalls of different diets have been around as long as the diets themselves. Is the ketogenic diet a great way to lose weight, or a low-carb jaunt into ill health? Are vegetarians missing out on essential vitamins? What exactly is the omnivore’s dilemma? Can Vegans Eat Sugar? And do paleo enthusiasts actually know what our ancient ancestors ate?

A study published this week in The American Journal of Clinical Nutrition can at least end one food debate: the impact of our choices on the climate. Our food system is responsible for a third of global emissions – livestock alone accounts for 14% – and what we eat could have a significant impact on what those emissions will be like in the future.

Using data collected from the US Centers for Disease Control and Prevention’s (CDC) National Health and Nutrition Examination Survey among nearly 17,000 American adults, researchers at Tulane University identified six popular American diets — vegan, vegetarian, pescetarian, paleo , keto and omnivore — and compared them based on environmental impact and diet quality. The ketogenic diet, which avoids carbs in favor of fats, was the most carbon-intensive, producing about 3 kg of carbon dioxide per 1,000 calories. The Paleo diet, which avoids grains, dairy and legumes, came in second with 2.6kg of CO2, while the omnivore diet came in at 2.2kg of CO2.

The diets with the lowest carbon footprints — vegan at 0.7kg of CO2 and vegetarian at 1.2kg — were also generally healthier than their high-carbon, meat-heavy alternatives, says lead author Diego Rose, director of the nutrition program at the School of the Tulane University Public Health and Tropical Medicine, calling it “an environmental and nutritional win-win.” There was one notable exception: The pescetarian diet scored the highest in terms of nutrition, based on the USDA’s Healthy Eating Index, at 3 pounds of CO2 per 1,000 calories. (The index is scored out of 100; the closer to 100, the healthier the diet.)

The report also found that if a third of the country’s omnivores, who accounted for 86% of survey respondents, refrained from eating meat on any given day, it would save 340 million car-kilometres of CO2 emissions. If a third gave up meat for a year, it would account for 4.9% of the total US emissions reduction target under the Paris Climate Agreement, while significantly improving diet quality.

“Giving up meat altogether is the easiest way to improve your (carbon) footprint and health,” says Rose. “But almost everyone can do better just by eating less of it.” Even climate-conscious ketovores and paleos have options, he adds. “Beef has eight to ten times the climate impact of chicken by weight. So even those on keto might do better if they switched to chicken and eggs for their protein.”

A version of this story also appears in the Climate is everything Newsletter. Click here to login.

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