A vegan diet is the least impactful on the climate compared to other popular diets, according to a new study published in The American Journal of Clinical Nutrition. The study, which compared popular diets on both nutrition quality and environmental impact, also found that keto diet and paleo diet score among the lowest on overall nutrition quality and were among the highest on carbon emissions.
The study compiled diet quality scores using data from more than 16,000 adult diets collected by the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey. Individual diets were assigned point values based on the federal Healthy Eating Index and average scores were calculated for those eating each type of diet. While other researchers have examined the nutritional impact of keto and paleo diets, this is the first study to measure the carbon footprints of each diet, as consumed by American adults, and compare them to other common diets, according to the study’s senior author, Diego Rose, professor and nutrition program director at Tulane University School of Public Health and Tropical Medicine. In a first-of-its-kind study has 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
A vegan diet was found to be the least impactful on climate, generating 0.7 kg of carbon dioxide per 1,000 calories consumed, less than a quarter of the impact of the keto diet. The vegan diet was followed by vegetarian and pescatarian diets in increasing impact.
“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.
Based on the nutritional values of the diets analyzed, the vegan and vegetarian diets scored highest on nutritional quality behind the pescatarian diet.
Keto- diets- worst for the Planet
On the other end of the spectrum, the study found that the keto diet, which prioritizes high amounts of fat and low amounts of carbs, was estimated to generate almost 3 kg of carbon dioxide for every 1,000 calories consumed. 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 2.6 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,” Rose said in a statement.
The omnivore diet—the most common diet, represented by 86 percent of survey participants— sat squarely in the middle of the pack of both quality and sustainability. 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. those on omnivorous diets opted for plant-forward diets such as the Mediterranean or meat-limiting DASH diets, both carbon footprints and nutritional quality scores improved.
“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 said. “Based on our results, that would reduce your footprint and be generally healthy.”
One third of all gas emissions from the food system
A 2021 United Nations-backed study found that 34 percent of greenhouse gas emissions come from the food system. The major share of those emissions come from food production, with beef being responsible for eight to 10 times more emissions than chicken production and over 20 times more emissions than nut and legume production.
While the environmental impacts of specific foods have been studied extensively, Rose said this study was important because “it considers how individuals select popular diets that are composed of a wide variety of foods.” Going forward, Rose still has questions about how to encourage eating habits that are better for people and the planet. “I think the next question is, ‘How would different policies affect outcomes and how could those move us toward healthier, more environmentally friendly diets?’” Rose said.
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