Tulane University has compared popular diets analysing their nutritional quality and environmental impact, revealing that the keto diet ranks the worst

It found that 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.

What are the keto and paleo diets?

The keto diet focuses on a high amount of fat and a low amount of carbohydrates. Shockingly, the diet is estimated to generate almost 3 kg of carbon dioxide for every 1,000 calories consumed.

The paleo diet shuns grains and beans in favour of meats, nuts and vegetables. It may come as a surprise, but the widely popular paleo diet received the next lowest diet quality score. Like keto, paleo also had a high carbon footprint, at 2.6 kg of carbon dioxide per 1,000 calories.

The data on diets were collected from more than 16,000 adults

Published in The American Journal of Clinical Nutrition, the study scores diets using data from more than 16,000 adult diets collected by the CDC’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.

Diego Rose, the study’s senior author, professor and nutrition program director at Tulane University School of Public Health and Tropical Medicine, explained that this is the first study to measure the carbon footprints of each U.S. diet, and compare them to other common diets.

‘We suspected the negative climate impacts because they’re meat-centric’

“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 added.

A vegan diet was found to be the least impactful to the environment

Whilst the keto diet ranked worst for climate, a vegan diet was the least impactful, generating 0.7 kg of carbon dioxide per 1,000 calories consumed. This comes as less than a quarter of the impact of the keto diet. The vegetarian and pescatarian diets followed behind the vegan diet in increasing climate impact.

Interstingly, the pescatarian diet scored highest on the nutritional quality of the diets analysed, with vegetarian and vegan diets following behind.

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86% of survey participants in the study consume an omnivore diet. Researchers found that this diet sits in the middle of the pack in terms of both quality and sustainability.

Based on the findings, if a third of those on omnivore diets began eating a vegetarian diet for any given day, it would be equivalent to eliminating 340 million passenger vehicle miles.

It is worth noting that those who consume an omnivorous diet should opt for plant-forward Mediterranean or fatty meat-limiting DASH diet versions, as this would improve carbon footprints and nutritional quality scores improved.

Climate change is one of the most pressing issues

“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. Our research also shows there’s a way to improve your health and footprint without giving up meat entirely.”

In fact, a 2021 United Nations-backed study found that the food industry is responsible for 34% of greenhouse gas emissions.

Beef production is responsible for 8-10 times more emissions than chicken production and over 20 times more 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.”

In the future, Rose wants 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 concluded.


  1. There is a difference between lifestyle and diet. With a diet, a person eats what they need to to lose weight and then goes right back to their bad habits again and gain back all the weight they lost. A lifestyle is a change that lasts a lifetime. As far as nutrition, on a keto diet you can eat all the vegetables you want. The main thing is to stay away from sugars, starches, refined carbohydrates. Can you verify you are not influenced by the sugar industry ?


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