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All kinds of products and processes are now being evaluated for sustainability, and the human diet is no exception. Three indexes are generally measured to represent the agricultural food system; carbon footprint (CF), water (consumption) footprint (WF), and ecological (land/sea use) footprint (EF). These are all higher for animal-based foods compared to plant foods, calorie-for-calorie.
Meat and emissions
Food production accounts for almost a quarter of human-related emissions, of which agriculture produces about 12% and livestock about 18%. Beef and dairy animals produce over 40% and 20% of livestock emissions respectively.
Dietary emissions are measured over the whole lifecycle from production to the table, including feed production (cereals), livestock breeding, fertilizer manufacture and application, and farm operational costs.
Environmental impact also includes the use of farmland exclusively for grass and cattle feed crops and a high energy input. It also includes emissions from fuel used to power farm machinery and at all stages of food production, such as the GHGs methane and nitrous oxide from ruminants and cultivated and fertilized soils.
The highest emissions are linked to animal product consumption, and beef or mutton consumption makes up 50% of the total in omnivores. Compared to pescetarian and vegetarian diets, emissions from meat consumption >100 g/day are about 50% higher. One study showed the GHG emission from mutton or beef to be 250 times higher than that of legumes.
Emissions from vegetarian and vegan diets are mostly from cereals, vegetable-based foods and sweets. The lack of significant disparity between them might be for several reasons. Firstly, real-life vegetarian diets use processed plant products like meat and dairy substitutes, like seitan or soy, which use more energy. Plant foods also have lower energy content gram for gram, and thus vegans must eat more than with ovo-lacto-vegetarian diets. However, many low-emission diets are not healthy.
Will it help to eat less meat?
Scientists estimate that shifting to plant-based diets would bring down the individual’s average carbon footprint by 900 kg of CO2/year, as much as that expended by a single passenger on a transatlantic commercial flight. On the other hand, a vegetarian diet reduces CO2 emissions by over 1200 kg of CO2e/year, and for vegans, over 1500 kg of CO2e/year less.
Apart from emissions, livestock farming has a larger WF than raising crops. Organic livestock farming uses less energy and enhances soil quality, and could help us move towards more sustainable meat-eating diets.
However, vegetarian or vegan diets help protect the environment and personal health. Vegetable cultivation occupies much smaller areas, reducing the EF, and has a much lower cumulative energy demand (CED) than with animal meat products. About a third of the world cereal production goes into animal feed, which puts pressure on the remaining arable land.
One-third of the total WF for agriculture is related to livestock farming, and any animal food has a larger WF than plant foods with equivalent nutritional value. For instance, pulses and nuts have a large WF, but still considerably less than beef. Beef, in fact, has WF twenty-times larger per calorie compared to starchy foods like cereals.
The protein WF of animal foods other than beef is 1.5 times higher than for legumes, and for beef it is 6 times larger. This is largely due to the poor efficiency with which feed is converted to animal protein. Moreover, industrial livestock farming pollutes large volumes of water compared to mixed or grazing systems.
We need to switch to diets which are not necessarily non-meat but low-meat. Plant products deliver nutrition most cost-effectively, compared to animal foods. This shift can enhance food security, relieve land stress and decrease the WF.
- Rosi A. et al., (2017). Environmental impact of omnivorous, ovo-lacto-vegetarian, and vegan diet. Scientific Reports. doi: 10.1038/s41598-017-06466-8
- Scarborough P. et al., (2014). Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK. Climatic Change. doi: 10.1007/s10584-014-1169-1
- Lacour C. et al., (2018). Environmental Impacts of Plant-Based Diets: How Does Organic Food Consumption Contribute to Environmental Sustainability? Frontiers in Nutrition. doi: 10.3389/fnut.2018.00008
- Wilson N. et al., (2013). Foods and Dietary Patterns That Are Healthy, Low-Cost, and Environmentally Sustainable: A Case Study of Optimization Modeling for New Zealand. PLOS ONE. https://doi.org/10.1371/journal.pone.0059648
- Cmu. edu. Rea S. (2015). Vegetarian and “Healthy” Diets Could Be More Harmful to the Environment. https://www.cmu.edu/news/stories/archives/2015/december/diet-and-environment.html
- Ourworld.unu.edu. Smith C. (2014). New Research Says Plant-based Diet Best for Planet and People. https://ourworld.unu.edu/en/new-research-says-plant-based-diet-best-for-planet-and-people
- Mekonnen M. M. et al., (2012). A Global Assessment of the Water Footprint of Farm Animal Products. Ecosystems. https://doi.org/10.1007/s10021-011-9517-8