Study of popular diets reveals fourfold difference in carbon footprints

For those following a keto or paleo diet, this can be hard to swallow.

A new study from Tulane University that compared popular diets on nutritional quality and environmental impact found that keto and paleo diets, as consumed by American adults, were among the lowest in terms of overall nutritional quality and among the highest in terms of carbon emissions.

The keto diet, which prioritizes high amounts of fat and low amounts of carbohydrates, is 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 second-lowest food quality score and also had a high carbon footprint, at 2.6 kg of carbon dioxide per 1000 calories.

The study, published in The American Journal of Clinical Nutrition, compiled diet quality scores using data from more than 16,000 adult diets collected by the CDC’s National Health and Nutrition Survey. Point values ​​were assigned to individual diets based on the Federal Healthy Eating Index and average scores were calculated for those who ate each type of diet.

The study’s lead author, Diego Rose, professor and director of the nutrition program at Tulane University’s School of Public Health and Tropical Medicine, said that although researchers looked at the nutritional impact keto and paleo diets, this is the first study to measure everyone’s carbon footprint. diet, as consumed by American adults, and compare them to other common diets.

“We suspected negative climate impacts because they’re meat-centric, but no one had really compared all of these diets — because they’re chosen by individuals, rather than prescribed by experts — to each other. using a common framework,” Rose said.

At the other end of the spectrum, a vegan diet was found to have the least impact on the climate, generating 0.7 kg of carbon dioxide per 1,000 calories consumed, less than a quarter of the impact of the diet. keto. The vegan diet has been followed by vegetarian and pescatarian diets with growing impact.

The pescatarian diet obtained the best results in terms of nutritional quality of the diets analyzed, followed by vegetarian and vegan diets.

The omnivorous diet — the most common diet, represented by 86% of survey participants — fell squarely in the middle of the quality and durability pack. Based on the results, if one-third of people on an omnivorous diet started eating a vegetarian diet, on average for any given day, that would be equivalent to eliminating 340 million passenger vehicle miles.

Notably, however, when those following an omnivorous diet opted for plant-based Mediterranean versions or DASH limiting fatty meat, carbon footprints and nutritional quality scores improved.

“Climate change is arguably one of the most pressing issues of our time, and many people want to switch to plant-based diets,” Rose said. “Based on our results, this would reduce your footprint and be generally healthy. Our research also shows that there is a way to improve your health and footprint without giving up meat entirely.”

A study supported by the United Nations in 2021 found that 34% of greenhouse gas emissions come from the food system. The bulk of these emissions come from food production, with beef being responsible for 8-10 times more emissions than chicken production and more than 20 times more emissions than nut and pulse production.

Although the environmental impacts of specific foods have been studied extensively, Rose said this study was important because “it considers how individuals select popular diets comprised 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 different policies would affect outcomes and how might they move us towards healthier and more environmentally friendly diets?” Rose said.