Animal agriculture has been called ‘factories in reverse’: in other words, you put a lot of food in to get a little food out. This is particularly true of beef and dairy. Most of the cornfields we see in the U.S. midwest feed livestock – not humans. In fact, worldwide, all grazing land and 66% of crop output are attributed to animal agriculture, whereas 34% of crop output is for human food crops. Also, there is additional incentive to change your diet: there are also many health benefits of eating plant-based. This webpage covers the difference in how we eat; the benefits of plant-based; how to start a more plant-based diet; and the science behind these claims.
The effect is tremendous. The average American eats 278 grams meat/day (not including fish), whereas the average European eats 195 grams (Lincke & Wolf, 2023). For comparison, consider that one quarter pounder is 112 grams. A lower impact diet would instead eat plant-based (e.g., burgers), with vegetarians adding eggs and dairy cheese. Notice that the effect on greenhouse gases (GHG) is nearly a one-ton step increase for each of the four diets. To see the individual effect of various foods, see Environmental Impacts of Food Production – Our World in Data.
The bar chart shows that the same three calorie values are given for each diet: 2000 kcal of what we should be eating, 2500 kcal of what we are actually eating, and 3250 kcal additionally includes food that is discarded at home and in stores. Therefore, reducing food thrown away (in stores and home) can save 30% of GHG, about 1/2 ton. Reducing meat and dairy consumption can reduce 1-3.5 tons of greenhouse gases, depending on the level of reduction and foods chosen.
To calculate your own greenhouse gases from diet, access Calculate Your Footprint and work with the Diet page. It personalizes according to your specific diet.
Benefits of a Plant-Based Diet
Benefits to You: Plant-based diets have been shown to be capable of reversing certain diseases, such as: heart disease, high blood pressure, non-alcoholic fatty liver disease, kidney disease, and diabetes. It also reduces the risk of these diseases, as well as strokes, Alzheimer’s, and certain cancers: breast, prostate, digestive, and blood cancers (Greger, 2015). A diet rich in vegetables and fruits can also slow or reduce the symptoms and risk of asthma, COPD, lung cancer, prostate cancer, and Parkinson’s. To learn more about how to best prevent or when possible treat these diseases naturally, access Michael Greger’s How Not to Die book. His How Not to Diet book describes how to best lose weight on a plant-based diet. His books are so well researched that about one third of his books are scientific research references.
Benefits to the Environment: Because of the multiplier inefficiencies of meat-based production, reducing meat consumption means reduced corn and soy farming, which leads to reduced water use and fertilizer, pesticide, and herbicide applications. Reduced chemical use results in much less water pollution and top soil loss. Reduced fertilizer means lower use of carbon-based fossil fuels. If existing animal feed farms are released back to nature, bushes and trees can regrow, providing more carbon sequestration and oxygen production, and enabling wildlife near extinction to recover. In addition, cattle have digestive systems particularly bad for the environment, resulting in high methane releases.
Foods that are low in greenhouse gases or other environmental indicator, thus tend to be low in all evaluated environmental indicators. Clark and Tilman (2017) conclude in their research study: “Indeed, for all indicators examined, ruminant meat (beef, goat and lamb/mutton) had impacts 20–100 times those of plants while milk, eggs, pork, poultry, and seafood had impacts 2–25 times higher than plants per kilocalorie of food produced.”
How To Eat a Plant-Based Diet
By following a more sustainable, whole-foods diet, you may improve your health, lose weight, and reduce your risk of various illnesses, including cardio-vascular disease, some cancers, and diabetes (Greger, 2016). The best way to do this is to emphasize whole foods, emphasizing the four plant-based food groups:
- vegetables: e.g., cruciferous (broccoli, bok choi, cabbage, kale, arugula), other greens, root/tuber vegetables, asparagus, squash, peppers, salad vegetables, mushrooms, sea vegetables;
- protein: lentils/peas, nuts, beans, seeds (sunflower, sesame);
- grains: rice, corn, quinoa, oats, buckwheat, wheat (whole), faro, barley, teff, rye, (Grains are a source of energy and plant protein);
- fruit: berries, melons, apples/pears/peaches, citrus, grapes, bananas, avocado, mango, …
Most plant foods contain fiber, which help reduce cholesterol levels and heart disease. See the Plant-Based Eatwell Guide for how to do plant-based right: https://plantbasedhealthprofessionals.com/wp-content/uploads/Plant-Basted-Eatwell-Guide-A4.pdf.Changing a diet can be difficult, because we have all developed eating patterns and comfort foods. From a health perspective, a whole foods diet of vegetables, beans/nuts, whole grains and fruit will help to achieve the health benefits described above (PCRM, 2024). For protein, include lentils, beans, nuts, soy/tofu/tempeh, and/or quinoa in your diet. Vegetables and whole grains also add protein and many nutrients. In particular raw or cooked greens and cruciferous vegetables, berries, and herbs are particularly nutritious (Greger, 2015). Grains should be prepared whole, not refined, and may include oats, millet, non-GMO corn, buckwheat, brown rice, teff, quinoa, and if you tolerate gluten: rye, barley, whole grain wheat.
Starting with food you know, such as lentil or bean soups, vegetable stir fries, potato or whole-grain pancakes (e.g., oat, buckwheat) may be a great way to ease into a more plant-based diet. To offer ideas of what might be possible for a lower impact (and healthier) diet, see “Whats for Dinner?”
A final important nutrient for plant-based diets is a B12 vitamin. B12 is produced by bacteria, and when we wash vegetables off, we wash off B12. When cows eat unwashed grasses, they get sufficient B12, so there may be sufficient B12 in diets with meat. However, meat diets often result in high fat, high cholesterol diets that often require blood pressure medicine. So the way I see it: you have a choice of taking B12 or high-blood pressure medicine. B12 is cheaper, more natural, and has no adverse health effects.
Why Meat is Problematic: The Science
Consider how much food is required if you eat food from crops, versus feeding them to an animal, until the animal reaches full size, and then eating the animal. It seems intuitive that eating the crops directly is more efficient and requires less food, land, and water and creates less waste and greenhouse gases than eating meat. The United Nations (UN) provided the following statistics within the UN Intergovernmental Panel on Climate Change (IPCC) AR5 (Smith et al., 2014). I have redrawn their Figure 11.9, below, by including the parts of the diagram related to food, but not including non-food processes, such as biofuels, forestry, and non-food industries.
What the diagram shows is that when considering cropland, human food makes up 36.2% of crops, while the remaining 63.8% is fed to livestock. Although only 36.2% of the crops grown are fed to humans, they provide 81.7% of the human diet (worldwide). The total input from crops and grazing land to ruminants (cows, sheep, goats) is 6.22 billion metric tons (Gt=gigatons) of dry matter; however, only 0.22 billion tons of meat is produced from that input. That is an efficiency rate of 0.22/6.22 or 3.5%. The efficiency rate for pigs and poultry is 22.8% (just less than ¼).
Considering waste, animal waste (just from the raising of animals) represents 55% of total agricultural waste. This does not include potential cropland, food processing, and consumption waste that is attributed to foods (including meat) in general. Manure is not cleaned up the same way as human waste and builds up in (and pollutes) rural communities. Another area for us to improve food efficiency is to reduce waste at the consumer (home, restaurant) level, which represents 15.4% of total agricultural waste.
To read the diagram below, recognize that the land (farming) is shown on the far left side and consumption (your home or restaurant visit) on the far right, with livestock raising and food processing (e.g., packaging, sales) in between. The red arrows indicate the amount of food that goes from one process to another, in gigatons (Gt) or billions of tons of dry matter. The black arrows pointing downwards indicate the amount of waste in Gt produced by each process.
Referring to the same UN IPCC diagram and considering land use, cropland makes up 12% of all Earth land, whereas grazing requires 35% of land. Since crops for humans make up 36% of crops grown from cropland, animal feed is used for the remaining 64% of cropland – plus all the grazing land. Humans use about 10 times the land for animal agriculture as for human crops (This is simplified, since cropland used for human food, including fruits and vegetables, is not as efficient as grains grown for livestock).
Not shown in this diagram is the amount of water used for livestock, including livestock watering, feed crop watering, and meat processing. Agriculture uses 70% of freshwater resources across our Earth. However, agriculture uses 1-40% in the northern hemisphere and 60-98% in the southern hemisphere, according to Our World in Data (quoting World Bank): U.S. 40%, India 90%, China 62%. Beef requires 1451 and 2714 liters per kg for beef and dairy beef, respectively. Lamb and pork fall between beef numbers. Farmed fish and nuts exceed beef numbers and cheese tops the chart at 5645 liters/kg. A link to the average water requirements per kg is shown at: https://ourworldindata.org/grapher/water-withdrawals-per-kg-poore.
Concerning climate change’s greenhouse gases, the two highest causes of greenhouse gases (listed by IPCC AR5) is enteric fermentation (32-40%) and agricultural soils (27+%). Enteric fermentation refers to the potent greenhouse gas, methane, generated by cow burps and farts. Manure and fertilizer laid on agricultural soils generate nearly an equal amount of greenhouse gas. Other agricultural greenhouse gases are caused by paddy rice cultivation (9-11%), biomass burning (6-12 %) and manure management (7-8 %) (Smith et al., 2014: p. 823). Again, animal agriculture is 100% responsible for enteric fermentation and manure management, and to a greater degree also for agricultural soils and biomass burning (which is forest burning to prepare an agricultural field for pasture or crops). To learn the greenhouse gas emissions for individual foods, see Our World in Data (link: https://ourworldindata.org/environmental-impacts-of-food).
RThese UN IPCC statistics are for average Earthlings. These land use, waste and food input statistics are very low for developed nations, since we eat more meat than average, and Americans much more so. The UN Food and Agriculture Organization (FAO) database (2024) indicates people in developed nations eat on average 56 Kg of meat per person per year; an American 82 Kg/year; and the average person from an undeveloped nation 22 Kg/year of meat. If people in developing nations acquire the same taste for more meat as in developed nations, then developing nations’ huge populations will clearly have a significant negative effect on the environment. Additional meat may more than double the demand for additional water and land (forests cut down, further reducing wildlife populations). Not only will the per person demand increase for the highly populated developing nations, but Earth’s population is also expected to increase from 8.2 billion today (2025) to 9.6 billion in 2050 and 10.9 billion in 2100. Thus, as renewable energy helps to reduce some greenhouse gas emissions, the Earth’s increasing meat consumption threatens to reverse progress.
References
Greger, M., & Stone, G. (2016). How Not To Die. Macmillan.
Lincke, S. & Wolf, J. (2023). Dietary modeling of greenhouse gases using OECD meat consumption/retail availability estimates. International Journal of Food Engineering, 19(1-2), 37-48. https://doi.org/10.1515/ijfe-2021-0352
Wedderburn-Bisshop, Gerard (2024) Consistent, Inclusive Emissions Accounting Identifies Agriculture as the Leading Cause of Climate Change.
PCRM (2024). Protein: Power Up with Plant-Based Protein. Physicians Committee for Responsible Medicine. From: https://www.pcrm.org/good-nutrition/nutrition-information/protein.
Michael Clark and David Tilman (2017) Comparative analysis of environmental impacts of agricultural production systems, agricultural input efficiency, and food choice. Environ. Res. Lett. 12 (2017) 064016, IOP Publishing.