Study of popular diets finds over fourfold difference in carbon footprints
Tulane University
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| Photo Credit: zuzyusa via Pixabay |
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.
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 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.
The
study's senior author Diego Rose, professor and nutrition program director at
Tulane University School of Public Health and Tropical Medicine, said that
while researchers have examined the nutritional impact of keto and paleo diets,
this is the first study to measure the carbon footprints of each diet, as
consumed by U.S. adults, 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 -- as they are chosen by individuals,
instead of prescribed by experts -- to each other using a common
framework," Rose said.
On the other end of the spectrum, 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
vegan diet was followed by vegetarian and pescatarian diets in increasing
impact.
The
pescatarian diet scored highest on nutritional quality of the diets analyzed,
with vegetarian and vegan diets following behind.
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 340 million passenger vehicle miles.
Notably,
however, when those on omnivorous diets opted for the plant-forward
Mediterranean or fatty meat-limiting DASH diet versions, both carbon footprints
and nutritional quality scores improved.
"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."
A
2021 United Nations-backed study found that 34% of greenhouse gas emissions
come from the food system. The major share of those emissions come from food
production, with beef being responsible for 8-10 times more emissions than
chicken production and over 20 times more emissions 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."
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 would different policies affect outcomes and how could those move us toward healthier, more environmentally friendly diets?" Rose said.