Study Shows Vegan Diet Is Twice As Sustainable As Vegetarian—And 4x As Omni Diets

March 2, 2023

Over the past several years, many separate teams of scientists around the world have found that the vegan diet is the most sustainable diet. A landmark meta-study in Science stated that vegans produce 73% less carbon footprint than an average omnivore diet. Another study published in Nature said that without a global adoption of plant-based diet, the world will go food-bankrupt by 2050. A UN-backed study also found that the vegan diet is the most wildlife-friendly diet for the biodiversity of the planet. And now we have a study that compares popular diets for their carbon footprint and nutritional value.

Five cows standing side by side with white and brown coat are looking at the camera on a grassy field.

Study of carbon footprints and nutritional quality by diet

Carbon emissions

A new study by Tulane University researchers compared self-reported diets and food intake of 16,000 subjects. The vast majority of them were omnivores (86.3%). In the order of prevalence, the rest were vegetarians (7.5%), pescatarians (4.7%), vegan (0.7%), keto (0.4%), and paleo (0.3%). By far the lowest carbon footprint diet was vegan (0.69 kg of CO2 per 1,000 calories). Vegan diet produces about 1/2 the carbon of the next eco-friendliest diet, which is vegetarian. This was followed by pescatarian, omnivore, paleo, and keto—yes, carbon emissions increases in direct proportion to animal-based foods.

“Of note, vegan diets had a significantly lower footprint than vegetarian diets, and these were significantly lower than all other diets, whereas omnivore, keto, and paleo diets were not significantly different in terms of carbon footprints,” write the authors of the study. Often, keto and paleo diets are packaged in a way that alludes to sustainability. Think “grass-fed” protein bars, “pasture-raised” cheeses, and “free-range” eggs. When it comes to actual carbon emissions, these distinctions don’t matter.

Diet quality

In terms of diet quality (measured using the federal Healthy Eating Index), brace yourself: pescatarian (58.76) scored the highest, followed by vegetarian (51.89) and vegan (51.65) diets. Then it was omnivore (48.92), paleo (45.03), and keto (43.69), in that order. Note that the nutritional quality between vegetarian and vegan diets is negligible.

Potential impact

The authors noted that even increasing the amount of fruit, vegetable, nuts, and legumes intake while reducing animal-based foods had a positive impact on both diet quality and carbon footprint. If 1/3 of omnivores eat vegetarian for just one day, the impact would be akin to eliminating 340 million passenger vehicle miles. If this happened year-round, that would mean 4.9% of reductions required to meet the U.S. targets in the Paris accords.

The study also provides interesting insight on demographics. As we’ve noted in the past, white people are the least represented among vegans per capita, and POCs are strongly represented among vegans per capita—especially Hispanics.

As a vegan who adopted the lifestyle overnight, I believe veganism is the best for protecting the planet, animals, and one’s own well-being. But it’s good to know that omnivores can also help by reducing their meat and replacing them with plant-based meals. Studies like these also provide useful insights, like using environmental justice as a focal point when discussing with white allies. POCs are significantly more likely than white people to be vegans—and that points up the fact that the oppressed are more likely to be empathetic to human and non-human suffering, both related to and beyond the climate crisis. And making them do the heavy lifting is environmental and racial injustice.

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Photo: Robert Bye via Unsplash


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