Paleo and Keto are among the least climate-friendly diets

People often adapt their diets to stay healthy – but what about changing what we eat for the health of the planet? It seems that some popular meal plans, like the ketogenic and paleo diets, aren’t very good for the Earth or your well-being, according to a recent study in The American Journal of Clinical Nutrition examined the environmental impact and nutritional quality of food products.

Our food choices can have significant consequences: What we eat contributes to about a third of all global greenhouse gas (GHG) emissions, taking into account agriculture and land use, the supply chain and our eating habits. Given the huge impact of food on climate change, it is important that dietary patterns become more sustainable. That starts with identifying food choices that are environmentally friendly, which is exactly what the study sought to discover.

“Since many people are experimenting with different diets, it’s useful to have a sense of the differences in their effects,” 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 influence what is produced and therefore the impact of our overall food production.”

Being vegan benefits the environment

The new research assessed the carbon footprint and quality of six popular diets, namely: vegan, vegetarian, peso, paleo, keto, and omnivore (which is basically everyone else’s diet). 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 diet but included seafood.

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

Those who ate 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. Keto dieters eat less than 50 grams of net carbs. The authors allowed for minimum amounts of some typically excluded foods to account for any minor deviations or accidental consumption of ingredients that the respondent may not have been aware of.

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

A vegetarian diet produced the second lowest emissions at 1.16 kilograms of carbon dioxide for every 1,000 calories consumed, the study authors found. The pessimist and omnivore diets were in the middle, creating about 1.66 and 2.23 kilograms of carbon dioxide for the same number of calories, respectively.

The scientists looked at the diets of more than 16,000 adults, which were collected by the National Center for Health Statistics’ national delegation of the National Health and Nutrition Examination Survey. Rose and colleagues also created their own database of the environmental impact of food staples, which they linked to the national data set to calculate the impact of each food item consumed. This allowed the authors to calculate 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 food is better for the planet. Consumers have the most 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 complete switch from meat could reduce food-related emissions by up to 73 percent. Additionally, if global food production were to shift to plant-based diets by 2050, 366 to 603 gigatons of carbon dioxide could also be sequestered from the regeneration of native vegetation in areas currently occupied by livestock.

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

Considering the environmental impact of food

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 background, are most important to most consumers’ food decision-making, [rather] rather than health or the environment,” says Rose.

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

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

The USDA’s Dietary Guidelines for Americans 2020-2025, which provide recommendations about what to eat 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 diet, which is relevant because climate change also affects human health. Reducing diet-related emissions by making better food choices can lead to improved health, notably by helping to reduce air pollution.

Implementing a carbon tax that raises the price of carbon-intensive foods can encourage consumers to choose foods with a lower impact, Keoleian says. But if that were to happen, programs that help lower-income households — like the Supplemental Nutrition Assistance Program (SNAP) — would be critical, as access and affordability of nutritious food is “particularly problematic,” he adds.

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

Facilitating consumers’ shift to environmentally sustainable diets requires a whole-of-society approach, Rose says—an approach that also includes policymakers, restaurants, food producers and eaters.

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