It’s true that keto and paleo diets are an effective way to lose weight (1, 2), reduce inflammation (3, 4), and improve your hormone profile (1).
But if you’re searching for the healthiest diet for your body and the planet, take keto and paleo off your list.
When compared to other popular diets, they fall behind in nutritional quality and sustainability, per a new study published in The American Journal of Clinical Nutrition (5).
The research, from Tulane University, is the first to compare six popular diets (omnivore, vegetarian, vegan, pescatarian, keto, and paleo) for both health and environmental impact. Keto and paleo diets were rated the lowest for overall nutritional quality and had the highest carbon footprint.
Here’s how the keto and paleo diets stack up to other popular diets, and what to eat instead.
What Did the Research Show?
The study, compiled diet quality scores using data from more than 16,000 adult diets collected by the Centers for Disease Control and Prevention (CDC) 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 pescatarian diet scored highest for nutritional quality, with vegetarian and vegan diets following closely behind. The omnivore diet—the most common diet, represented by 86 percent of survey participants—sat right in the middle of the pack. The paleo and keto diets ranked worst for nutrition.
To measure the carbon footprint of each diet, the researchers compared the carbon dioxide emissions—a key metric in measuring environmental impact (6)—per 1,000 calories of food.
A vegan diet was found to be the least impactful on climate, generating 0.7 kg of carbon dioxide per 1,000 calories consumed. The vegan diet was closely followed by the vegetarian and pescatarian diets. The omnivore diet was right in the middle. Last in line: the paleo (at 2.6 kg) and keto diets (at 3 kg).
How to Eat More Sustainably
“We suspected the negative climate impacts [of keto and paleo diets] because they’re meat-centric,” said Diego Rose, the study’s senior author. 34 percent of greenhouse gases come from the food system, a major share of those coming from meat production, according to a study published in Nature (7).
Beef is responsible for eight to ten times more emissions than chicken production, and over 20 times more than common plant-based alternatives like beans (8). This is exactly why many are leaning towards plant-based options.
“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,” said Rose. “Based on our results, that would reduce your footprint and be generally healthy.” If a third of those on omnivore diets began eating a vegetarian diet on any given day, it would be the equivalent of eliminating 340 million passenger vehicle miles, per the study.
“Our research also shows there’s a way to improve your health and footprint without giving up meat entirely,” Rose adds. According to the study, when those on omnivorous diets opted for plant-forward Mediterranean or fatty meat-limiting DASH diet versions, both carbon footprints and nutritional quality scores improved.
Is a Plant-Based Diet Healthy?
Not necessarily. Like any diet, the health of a plant-based diet really comes down to the specific foods you’re eating. A diet laden with ultra-processed food products—whether plant-based or not—can increase your risk of early death (9). This means the jury is still out on plant-based products like Beyond steak.
What’s more, while not as environmentally friendly, a pescatarian diet was still ranked healthier than plant-based options like the vegan or vegetarian diet, per the study.
According to Rose, your best bet is to opt for a plant-forward diet that prioritizes whole foods. The Mediterranean diet—which emphasizes foods like fruits and vegetables, beans, nuts, seeds, whole grains, and heart-healthy fats like fish, olive oil, and avocados—is a good place to start.