What is the lowest-carbon protein?

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Swapping a beef burger for a plant-based alternative can significantly reduce our individual carbon emissions (Credit: Alamy)

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.

When it comes to reducing our individual carbon emissions, one of the most impactful steps we can take is to eat more sustainably. Global food production is responsible for 35% of all human-caused greenhouse gas emissions. While animal products account for the bulk of our dietary emissions, they provide only 20% of the world's calories.

Animal products, such as dairy, eggs, fish and meat, are known to be good sources of protein, and getting the right amount of protein is essential for our bodies to grow and repair (Read more about how much protein we really need to consume).

For those who want to eat a low-carbon diet that is also nutritious, getting the right level of protein can be challenging. The picture is complicated by the huge range of products available to us, many of which assert that they are "carbon neutral" or "sustainable" without always backing up these claims.

So, what would a protein-rich, low-carbon diet really look like? Just how bad for the climate are meat and dairy? How much more sustainable is it to only eat plant-based proteins, such as tofu, chickpeas and peas? Is it better to cut out cheese or chicken? Which animal-free alternatives have the lowest emissions' output?

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, who studies the lifecycle of food at Swiss research institute Agroscope.

Meat

According to the analysis, beef generates 49.9kg of  CO2 equivalent, or CO2e, per 100g of protein, equivalent to the amount in 2.35 steaks. The proteins with the second-highest greenhouse gas (GHG) footprint are lamb and mutton, which generate 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, director of sustainable diets at the World Resources Institute.

Cows, sheep and goats are all ruminants, animals with more than one stomach chamber that belch out methane when they digest their food. Although shorter-lived in the atmosphere, methane is a highly potent gas that has a global warming impact 84 times higher than carbon dioxide (CO2) over a 20-year period.

In addition to livestock's high methane output, greenhouse gases are emitted to produce and transport animal feed and run the livestock farms, says Sophie Marbach, a physicist and researcher at the National Centre for Scientific Research in France who carried out an analysis of the carbon footprint of meat and dairy proteins in 2021.

Beef from a dairy herd has a lower greenhouse gas footprint than meat from a beef herd because you get more food in return for all the resources you invest in the cow (feed, land, water and fertiliser), says Bordier. "[In addition to beef], these cows produce milk, which also tends to be used as feed [for other animals]... So it's more efficient overall," she says.

Dairy cows usually produce high milk yields for about three years, after which they are slaughtered and their meat is used for beef.

Meat from small, non-ruminant animals, such as chicken, turkey, rabbit and duck, has a much lower GHG footprint than beef and lamb. Chicken, for example, has a GHG footprint almost nine times lower than beef's – generating 5.7kg of CO2e per 100g of protein.

That's "quite low", says Sarah Bridle, professor of food, climate and society at the University of York in the UK. "It is really similar to farmed fish and eggs."

Pork's GHG footprint (7.6kg) is about 6.5 times lower than beef's and 1.4 times higher than poultry's (5.7kg).

Dairy

It is cheese, not chicken or pork, that generates the third-highest emissions in agriculture, after 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".

The GHG footprint of cheese (10.8kg of CO2e per 100g of protein) is almost twice as high as chicken's and also higher than pork and eggs (4.2kg of CO2e).

The dietary emissions can vary greatly depending on the type of cheese you're eating. Harder cheeses, such as parmesan, are more carbon-intensive than soft cheeses because they are made with more milk, says Bridle. Soft cheeses contain more water – there's 50% more water in cottage cheese than in cheddar, for example, she says.

The GHG footprint of cow's cheese is similar to that of goat's or sheep's milk cheeses "because they're all ruminants," says Bridle. "But cow's cheese is probably the most efficient because dairy cows produce vast amounts of milk." According to data from the UK's Department for Environment, Food and Rural Affairs, a dairy cow produced an average of 8,200 litres (1,800 gallons) last year.

Yoghurt, meanwhile, is surprisingly low-carbon, 2.7kg of CO2e per 100g of protein, as not much milk is needed to produce it (much less than in the case of 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,says Marbach. 

Plants

Animal products are responsible for 57% of global food-related emissions, compared to plant-based foods which contribute 29% of the total.

The UK's Climate Change Committee (CCC) has recommended a 20% reduction in meat and dairy consumption by 2030, rising to 35% by 2050 for meat, to meet the country's climate goals.

The lowest emissions option would be to adopt a vegan diet and cut out meat and dairy altogether. If the whole world went vegan, global food-related emissions would fall by up to 70% by 2050, according to a study by the Oxford Martin School at the University of Oxford.

A diet rich in peas, pulses and nuts can be incredibly low-carbon. Producing 100g of protein from peas emits just 0.4kg of CO2e. This is almost 90 times less than getting the same amount of protein from beef. Other pulses, such as lentils, have a GHG footprint of 0.8kg of CO2e. Tofu production, meanwhile, generates 2.0kg of CO2e per 100g – these emissions are mostly linked to the clearance of land for soy production, says Bridle.

By crossbreeding wild chickpeas with cultivated varieties, US company Nucicer has created high-protein chickpea powder, which it says also lowers the CO2e of the crop. The powder can be used as gluten-free flour in pasta and baked goods.

By increasing the protein content, Nucicer is able to produce more protein per acre and reduce the overall amount of energy and water needed, says Kathyrn Cook, the company's chief executive and cofounder. "That really helps with the environmental impact of our protein sources," she says. Chickpeas are also highly water-efficient and fix nitrogen from the air into the soil, which is vital for plant growth, she adds.

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