The trendiest ways to lose weight may also be the unhealthiest and least environmentally friendly, new research has found.
People looking to drop a few pounds often turn to ketogenic and paleo diets, but according to a Tulane University study, these weight loss approaches scored the lowest for overall nutritional quality and the highest for carbon emissions.
“We suspect negative climate impacts because they're meat-centric, but no one has really compared all of these diets — because they're chosen by individuals, not prescribed by experts — against each other using a common framework,” study senior author Diego Ross said in a statement Tuesday.
The study, published in the American Journal of Clinical Nutrition, examined six popular diets using data from the Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey.
Diets were assigned scores based on the Federal Healthy Eating Index, and the mean scores were calculated for the 16,000 participants who ate each diet.
The ketogenic diet—which Gwyneth Paltrow, Halle Berry, and Kim Kardashian are all celebrity advocates—prioritizes high-fat and low-carb. This diet is estimated to produce about 6.6 pounds of carbon dioxide for every 1,000 calories consumed.
The Paleo diet, which avoids grains and legumes in favor of meat, nuts and vegetables, had the next highest diet quality score and also had a high carbon footprint, emitting 5.7 pounds of carbon dioxide per 1,000 calories.
Miley Cyrus and Uma Thurman are among the paleo dieters who focus on eating unprocessed foods that people in the Stone Age could have hunted or gathered.
The vegan diet has the lowest carbon footprint, producing just 1.5 pounds of carbon dioxide for every 1,000 calories consumed—less than 25 percent of the carbon dioxide produced by a ketogenic diet.
Pescatarian diets (eating fish, but no animal meat) scored highest for the nutritional quality of the diets analyzed, followed by vegetarian and vegan diets.
The study found that an omnivorous diet (eating meat and vegetables) – the most common diet, consumed by 86% of respondents – was in the middle for quality and sustainability.
A United Nations-backed study published in 2021 determined that 34 percent of greenhouse gas emissions come from the food system, or food production. Beef emits 8 to 10 times as much as chicken production and more than 20 times as much as nut and soy production.
The researchers noted that if a third of the participating omnivores became vegetarians, an average of 340 million passenger vehicle miles could be saved each day.
“Climate change is arguably one of the most pressing issues of our time, and many people are interested in switching to a plant-based diet,” Ross said. “Based on our results, this will reduce your footprint and be healthy overall. Our research also suggests that there is a way to improve your health and footprint without giving up meat entirely.”
