A new study published in The American Journal of Clinical Nutrition compared popular diets on both nutritional quality and environmental impact and found that the keto and paleo diets, as eaten by American adults, scored among the lowest on overall nutrition quality and were among the highest on carbon emissions.

The study, whose senior author is Diego Rose, professor and nutrition program director at the School of Public Health and Tropical Medicine, compiled diet quality scores using data from more than 16,000 adult diets collected by the CDC’s National Health and Nutrition Examination Survey.  

Rose said that this is the first study to measure the carbon footprints of each diet and compare them to other common diets.

“We suspected the negative climate impacts because they’re meat-centric, but no one had really compared all these diets,” Rose said.

Keto and Vegan plate
A new study has found that foods featured in the keto diet — which prioritizes high amounts of fat and low amounts of carbs — produce the most carbon emissions of six popular diets, while the vegan diet is associated with the lowest carbon footprint.

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. 

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 pescatarian diet scored highest on nutritional quality of the diets analyzed.

The omnivore diet — the most common diet, represented by 86% 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 carbon emissions of 340 million passenger vehicle miles.