Paleo and keto diets aren’t great for you or the planet, study says

People often adjust their diets to keep themselves healthy—but what about changing what we eat for the health of the planet? It appears that some popular meal plans, such as ketogenic and Paleolithic diets, aren’t very good for Earth or for your wellness, according to a recent study in The American Journal of Clinical Nutrition  looked into the environmental impact and nutrition quality of food commodities.

Our food choices can have major consequences: What we eat contributes about a third of all greenhouse gas (GHG) emissions globally, when accounting for agriculture and land use, supply chain, and our dietary habits. Given food’s huge impact on climate change, it’s important that dietary patterns become more sustainable. This begins with identifying the food choices that are environmentally friendly, which is exactly what the study sought to find out.

“Given that many people are experimenting with different diets, it’s helpful to have a sense of the differences in their impacts,” says Diego Rose, study author and director of nutrition at Tulane University. “What individuals choose to eat sends signals to producers about what to produce, so individual behaviors can affect what gets produced and thus the impacts from our overall food production.”

Going vegan benefits the environment

The new research assessed the carbon footprint and quality of six popular diets, namely: vegan, vegetarian, pescatarian, Paleolithic, ketogenic, and omnivore (which, basically, is the diet of everyone else). Vegans, as defined by the study, ate very little meat and dairy: less than 0.5 ounces of the former and less than 0.25 cups of the latter each day. Meanwhile, vegetarians ate less than 0.5 ounces of meat, poultry, and seafood combined; a pescatarian diet was similar to a vegetarian one, but included seafood.

[Related: How to eat sustainably without sacrificing your favorite foods.]

Those who consumed meat but ate less than 0.5 ounces of grains and legumes per day, and less than 0.25 cups of dairy, followed the Paleo diet. People who have a keto diet eat less than 50 grams of net carbohydrates. The authors allowed minimal amounts of some typically excluded foods to account for any minor deviations or accidental consumption of ingredients that the respondent might not have known.

The findings showed that Paleo and keto are among the highest in carbon emissions and lowest in nutrition quality. The researchers estimated these diets produce about 2.6 and almost 3 kilograms of carbon dioxide for every 1,000 calories consumed, respectively. Meanwhile, a vegan diet was the best for the environment, which generates about 0.7 kg of carbon dioxide for the same number of calories. The amount of dietary GHG emissions significantly decreased when meats are replaced with plant proteins.

A vegetarian diet produces the second lowest emissions at 1.16 kilograms of carbon dioxide for every 1,000 calories consumed, the study authors found. Pescatarian and omnivore diets fared in the middle, generating about 1.66 and 2.23 kilograms of carbon dioxide for the same number of calories, respectively.

The scientists reviewed the diets of more than 16,000 adults, collected by the National Center for Health Statistics’ nationally representative National Health and Nutrition Examination Survey. Rose and his co-authors’ also created their own database of environmental impacts of food commodities, which they linked to the national dataset to calculate the impact of each food item consumed. This allowed the authors to compute an average carbon footprint for each diet type.

[Related: Why seaweed farming could be the next big thing in sustainability.]

The study shows, in line with previous research, that eating less animal-based food is best for the planet. Consumers have the greatest influence in reducing carbon emissions from the food system by shifting their diets to lower carbon-intensive foods, says Gregory A. Keoleian, director of the Center for Sustainable Systems at the University of Michigan who was not involved in the study. For example, a change away from meat altogether could reduce food-related emissions by up to 73 percent. Additionally, if global food production shifted to plant-based diets by 2050, there could also be sequestration of 366 to 603 gigatons of carbon dioxide from native vegetation regrowth in areas currently occupied by animal agriculture.

“All animal-based foods combined—red meat, poultry, fish or seafood, eggs, dairy, and animal-based fats—represent 82 percent of the baseline diet carbon footprint,” says Keoleian. “Plant-based proteins such as legumes, soy products, and nuts and seeds will dramatically reduce impacts.”

Considering foods’ environmental impact

As of 2018, about 5 percent of Americans are vegetarian, and only 2 percent have a vegan diet. “Taste and price, along with cultural and social backgrounds, are more important for most consumers’ decision-making about food, [rather] than health or the environment,” says Rose.

To encourage consumers to shift to environmentally friendly diets, he says policymakers could start by educating the public about the environmental impacts of food, either through dietary recommendations or food labels. One recent study found that around 16 percent of a nationally representative sample might be receptive to changing their diet to follow environmentally sustainable guidelines.

[Related: Eating seafood can be more sustainable and healthy than red meat.]

The Agriculture Department’s Dietary Guidelines for Americans 2020-2025 that provides recommendations on what to consume to support good health, reduce the risk of chronic disease, and meet nutrient needs may play a role. Keoleian says these guidelines can be expanded to include information about the environmental impact of diets, which is relevant because climate change influences human health, too. Reducing diet-related emissions by making better food choices may lead to improved health, mostly by helping reduce air pollution. 

Applying a carbon tax that raises the price of carbon-intensive foods may encourage consumers to opt for lower-impact foods, says Keoleian. But if this were to happen, programs that assist lower-income households—like the Supplemental Nutrition Assistance Program (SNAP)—would be critical since the access and affordability of nutritious food is “particularly problematic,” he adds.

They could also enact programs that subsidize greener food production, promote more sustainable versions of livestock, and offer alternatives to animal-based foods, says Rose. Furthermore, restaurants can place more sustainable foods higher up on the menu and develop new recipes with less meat but more flavor,  he adds.

To make it easier for consumers to shift to environmentally sustainable diets, a whole-of-society approach is needed, Rose says—one that includes policymakers, restaurants, food producers, and eaters, too.