The trendiest ways to lose weight may also be the unhealthiest and the worst for the environment, new research has found.
People hoping to shed a few pounds often turn to keto and paleo diets, but, according to a Tulane University study, those weight loss methods score among the lowest on overall nutrition quality and among the highest on carbon emissions.
“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,” study senior author Diego Rose said in a statement Tuesday.
Published in the American Journal of Clinical Nutrition, the study examined six popular diets using data from the National Health and Nutrition Examination Survey by the Centers for Disease Control and Prevention.
Diets were assigned point values based on the federal Healthy Eating Index and average scores were calculated for the 16,000 participants eating each type of diet.
The keto diet — which counts Gwyneth Paltrow, Halle Berry and Kim Kardashian as celebrity devotees — prioritizes high amounts of fat and low amounts of carbs. The diet was estimated to generate around 6.6 pounds 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 5.7 pounds of carbon dioxide per 1,000 calories.
Miley Cyrus and Uma Thurman are among the paleo dieters focused on consuming unprocessed foods that people in the Stone Age would have been able to hunt or gather.
Vegan diets had the lowest carbon footprint, generating only 1.5 pounds of carbon dioxide per 1,000 calories consumed — less than 25% of the CO2 generated by the keto diet.
The pescatarian diet (eating fish, but not animal meat) scored highest on nutritional quality of the diets analyzed, with vegetarian and vegan diets following behind.
The study found the omnivore diet (eating meats and vegetables) — the most common diet, consumed by 86% of those surveyed — landed in the middle for quality and sustainability.
A study released in 2021 that was backed by United Nations determined that 34% of greenhouse gas emissions come from the food system, namely food production. Beef was responsible for eight to 10 times more emissions than chicken production and more than 20 times more emissions than nut and legume production.
Researchers noted that if a third of participating omnivores began eating a vegetarian diet, 340 million passenger vehicle miles could be eliminated daily on average.
“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.”