Pescetarian diets prevail in nutrition study while keto and paleo labeled bad news for climate change

01 Mar 2023 --- Researchers at the Tulane University of Louisiana, US, have revealed significant differences in the environmental footprint and nutritional density of popular diets. The pescetarian diet was the most nutritious, followed by vegetarian and vegan diets. The omnivore diet came out in the middle, while the least nutritious diets were the ketogenic and paleo diets, which also were responsible for the highest carbon emissions.

“We suspected the negative climate impacts [of omnivore diets] 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,” says Diego Rose, lead author of the study and professor and nutrition program director at the Tulane University School of Public Health and Tropical Medicine.

Published in the American Journal of Clinical Nutrition, the study included 16,000 adults, using data from the National Health and Nutrition Examination Survey. 

Nutritional differences
The data was measured by assigning point values based on the federal healthy eating index – measuring how the diets align with recommendations from the Dietary Guidelines for Americans. 

The paleo diet (avoiding grains and beans while favoring meat, nuts and vegetables) came second in terms of least nutritional density after the ketogenic diet (eating high amounts of fat and protein while avoiding carbs). 

The most common diet – the omnivore diet – was followed by 86% of the survey participants and “sat squarely in the middle” in terms of both nutritional quality and environmental sustainability. 

The vegan diet was shown to be kindest to the planet, with 0.7 kg of carbon dioxide generated per 1,000 calories.The findings also showed that, on average, if a third of the participants were to start a vegetarian diet on any given day, it would equal “eliminating 340 million passenger vehicle miles.”

The researchers also say that both nutritional quality and carbon emissions improved when omnivorous diets were exchanged for Mediterranean diets and when reducing fatty meat intake. 

Environmental footprints
The keto diet generated 3 kg of carbon dioxide per 1,000 calories consumed. The paleo diet was just a little behind with 2.6 kg per 1,000 calories. 

The vegan diet was shown to be kindest to the planet, as per 1,000 calories consumed, it generated 0.7 kg of carbon dioxide, followed by the vegetarian and pescetarian diet. 

“Climate change is arguably one of the most pressing problems of our time, and many people are interested in moving to a plant-based diet,” says Rose.

“Based on our results, that would reduce your footprint and be generally healthy. Our research also shows a way to improve your health and footprint without giving up meat entirely,” he says.

A study backed by the United Nations in 2021 found that 34% of greenhouse gas emissions come from the current food system and the majority from producing foods. It showed that beef production is responsible for eight to ten times more emissions than chicken production and more than 20 times higher than nut and legume production.

Recently, researchers at the University of California, US, showed that healthier diets also positively impact environmental footprints and that making simple substitutions in any diet can help people and the planet improve health. 

Moving forward, Rose says that research will examine how different policies affect outcomes and how they could help society move to healthier and more environmentally friendly diets.

Edited by Beatrice Wihlander