Finding protein-rich foods that are good for the climate can be complex. Isabelle Gerretsen digs into the data to understand which food choices can help us curb emissions.
One of the most effective steps we can take to reduce our individual carbon footprint is to eat more sustainably. Food production accounts for 35% of all human-caused greenhouse gas emissions. While animal products contribute the majority of our dietary emissions, they only provide 20% of the world’s calories.
Animal products, such as dairy, eggs, fish, and meat, are known to be high in protein, and getting enough protein is critical for our bodies to grow and repair (Read more about how much protein we really need to consume).
Getting the right level of protein can be difficult for those who want to eat a low-carbon diet that is also nutritious. The picture is complicated by the vast array of products on the market, many of which claim to be “carbon neutral” or “sustainable” without always backing up these claims.
So, what exactly is a protein-rich, low-carbon diet? How bad are meat and dairy for the environment? How much more environmentally friendly is it to eat only plant-based proteins like tofu, chickpeas, and peas? Is it better to forego the cheese or the chicken? Which animal-free alternatives produce the fewest emissions?
BBC Future set out to answer these questions using data from the largest ever analysis of food systems, compiled by Joseph Poore, a researcher at the University of Oxford, and Thomas Nemecek, a food lifecycle researcher at the Swiss research institute Agroscope.
According to the study, beef produces 49.9kg of CO2 equivalent, or CO2e, per 100g of protein, which is equivalent to four steaks. Lamb and mutton have the second-highest greenhouse gas (GHG) footprint, generating 19.9kg of CO2e per 100g.
“There’s so much emphasis on beef that people often forget about other types of meat and their impacts,” says Anne Bordier, World Resources Institute’s director of sustainable diets.
Cows, sheep, and goats are all ruminants, meaning they have multiple stomach chambers and expel methane when they digest their food. Although it has a shorter lifetime in the atmosphere, methane is a highly potent gas with an 84-fold greater global warming impact than carbon dioxide (CO2) over a 20-year period.
In addition to the high methane output of livestock, greenhouse gases are emitted to produce and transport animal feed and run livestock farms, according to Sophie Marbach, a physicist and researcher at France’s National Centre for Scientific Research who conducted a carbon footprint analysis of meat and dairy proteins in 2021.
According to Bordier, beef from a dairy herd has a lower greenhouse gas footprint than beef from a beef herd because you get more food for all the resources you invest in the cow (feed, land, water, and fertiliser). “These cows produce milk, which is used as feed [for other animals] in addition to beef… As a result, it is more efficient overall “she claims. Dairy cows typically produce high milk yields for three years before being slaughtered and their meat used for beef.
Meat from small, non-ruminant animals, such as chicken, turkey, rabbit, and duck, emits significantly less GHG than beef and lamb. Chicken, for example, emits 5.7kg of CO2e per 100g of protein, which is nearly nine times less than beef.
That is “quite low,” according to Sarah Bridle, professor of food, climate, and society at the University of York in the United Kingdom. “It’s a lot like farmed fish and eggs.”
The GHG footprint of pork (7.6kg) is approximately 6.5 times lower than that of beef and 1.4 times higher than that of poultry (5.7kg).
Cheese, not chicken or pork, is the third-highest emitter in agriculture, trailing only lamb and beef.
“There’s this consensus that ‘being vegetarian is great’, but then we sort of forget that cheese is actually pretty carbon intensive,” says Marbach, noting that this is due to cows’ high methane output and the fact that they require “a lot of inputs for not much output”.
Cheese has a higher GHG footprint than chicken (10.8kg of CO2e per 100g of protein), as well as pork and eggs (4.2kg of CO2e).
The dietary emissions differ greatly depending on the type of cheese consumed. Harder cheeses, such as parmesan, have a higher carbon content. Bridle claims that hard cheeses are more intense than soft cheeses because they are made with more milk. She claims that soft cheeses have more water than hard cheeses, with cottage cheese having 50% more water than cheddar.
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Cow’s cheese has a similar GHG footprint to goat’s or sheep’s milk cheeses “because they’re all ruminants,” according to Bridle. “However, cow’s cheese is likely the most efficient because dairy cows produce a large amount of milk.” A dairy cow produced an average of 8,200 litres (1,800 gallons) of milk last year, according to data from the UK’s Department for Environment, Food, and Rural Affairs.
Yoghurt, on the other hand, is surprisingly low-carbon, with 2.7kg of CO2e per 100g of protein, because not much milk is required to produce it (much less than cheese) and there are a number of by-products, such as cream and butter, which means the GHG footprint is distributed across numerous food items, according to Marbach.