People often adjust their diets to stay healthy – but how about changing what we eat for the health of the planet? It seems that some popular meal plans, such as ketogenic and paleolithic diets, aren’t so good for the earth or your health, according to a recent study in American Journal of Clinical Nutrition It looked at the environmental impact and nutritional quality of food commodities.
Our food choices can have serious consequences: What we eat contributes to about a third of global greenhouse gas (GHG) emissions, when accounting for agriculture, land use, supply chain, and our dietary habits. Given the huge impact of food on climate change, it is important that dietary patterns become more sustainable. This starts with identifying environmentally friendly food choices, which is exactly what the study sought to find.
“Given that so many people try different diets, it’s helpful to have a sense of the differences in their effects,” says Diego Rose, MD, 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 thus the effects from our overall food production.”
Going vegan is good for the environment
The new research assessed the carbon footprint and quality of six popular diets: vegan, vegetarian, vegan, vegan, paleolithic, ketogenic, and carnivore (which is basically everyone else’s diet). Vegetarians, according to the study’s definition, 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, the vegetarians ate less than 0.5 ounces of meat, poultry, and seafood combined; The vegetarian diet was similar to the 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 cup of dairy products, followed the paleo diet. People on the keto diet eat less than 50 grams of net carbs. The authors allowed small amounts of some normally excluded foods to account for any minor deviations or accidental consumption of ingredients that the respondent might not be aware of.
Results show that paleo and keto are among the highest in carbon emissions and lowest in nutritional quality. The researchers estimated that these diets produce about 2.6 and 3 kilograms of carbon dioxide for every 1,000 calories consumed, respectively. Meanwhile, a vegetarian diet was best for the environment, generating about 0.7 kilograms of carbon dioxide for the same number of calories. The amount of dietary greenhouse gas emissions decreased significantly when meat was replaced with vegetable proteins.
The study authors found that a vegan diet produces the second lowest emissions at 1.16 kilograms of carbon dioxide per 1,000 calories consumed. Pescatarian and omnivore diets were in the middle, producing about 1.66 and 2.23 kg 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’ National Health and Nutrition Examination Survey. Rose and his colleagues also created their own database of the environmental impacts of food commodities, and linked it 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 foods is better for the planet. Consumers have the greatest influence in reducing carbon emissions from the food system by switching their diets to foods that are lower in carbon density, says Gregory A. Kewlian, director of the Center for Sustainable Systems at the University of Michigan who was not involved in the study. For example, changing away from meat entirely can reduce food-related emissions by up to 73 percent. In addition, if global food production shifts to a plant-based diet by 2050, there may also be 366 to 603 gigatonnes of CO2 sequestered from the regrowth of native plants in areas currently occupied by animal agriculture.
“All animal foods combined—red meat, poultry, fish or seafood, eggs, dairy products, and animal fats—account for 82 percent of the carbon footprint of the primary diet,” says Keulian. “Plant proteins such as legumes, soy products, nuts, and seeds will greatly reduce the effects.”
Consider the environmental impact of food
As of 2018, about 5 percent of Americans are vegetarian, and only 2 percent follow a vegan diet. “Taste and price, along with cultural and social backgrounds, are more important when making decisions for most consumers about food, [rather] health or the environment,” says Rose.
To encourage consumers to switch to greener diets, he says policymakers can start by educating the public about the environmental impacts of foods, either through dietary recommendations or food labels. One recent study found that about 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 Department of Agriculture’s 2020-2025 Dietary Guidelines for Americans, which provide recommendations on what to consume to support good health, reduce chronic disease risk, and meet nutritional needs, may play a role. Colian says these guidelines could be expanded to include information about the environmental impact of diets, which is important because climate change affects human health, too. Reducing diet-related emissions by making better food choices may improve health, mostly by helping to reduce air pollution.
Implementing a carbon tax that raises the price of carbon-dense foods may encourage consumers to choose low-impact foods, says Kiulian. But if this happens, programs that help low-income families — such as the Supplemental Nutrition Assistance Program (SNAP) — will be crucial because access to and affordability of nutritious food “is particularly problematic,” he adds.
They can also enact programs that support greener food production, promote more sustainable versions of livestock, and offer alternatives to animal-based foods, Rose says. What’s more, restaurants can put more sustainable foods at the top of the menu and develop new recipes with less meat but more flavor, he adds.
To facilitate consumers’ transition to environmentally sustainable food systems, a whole-of-society approach is needed, Rose says — one that includes policymakers, restaurants, food producers and eaters as well.