Archive:000/Limits to sustainable animal consumption

Tl;dr: The limit is about 17 g protein/day per person - in total, dairy and meat, from all grass-fed animals and wild-caught fish.

Farming

• Vegans rightly point out that meat-containing diets require more land (and thus more deforestation). Feeding crops to animals is a net loss of protein and calories. But...
• Pro-meat folks rightly point out that some land is only suited for grazing animals. And unlike humans, cows can live on eating grass(...)( and so can buffalo, sheep and goats. But chickens & pigs can't. ).

This raises a more important question:

If farm animals only ever ate...

• grasses and other plants from pasture & range(...)( especially from biodiverse natural lands that keep a lot of carbon stored in the roots of plants ), and
• the parts of food crops that humans can't eat(...)( for example corn cobs after the kernels have been removed (ruminants can digest certain kinds of fibrous matter that other species can't) ),

and never...

• human-edible food crops(...)( including corn and soy as those could be made into flour ) (...)( Grey area: Perhaps also include "spent grains" and "fryer waste oil" here, because the original materials were human-edible, and the downgrading was a choice. ), nor
• crops grown specifically for animal feed(...)( Grey area: Perhaps also include the more superficial types of "pasture" that are monoculture-like and don't keep a lot of permanent roots. The exact definition can be specified in the answer to the question. ),

how much animal protein(...)( from meat, milk and/or eggs etc ) could be produced?

Clearly it's less than the status quo, as there are fewer sources of feed. But how much less?

Estimate

About 12 grams of animal protein per day, per capita, globally.
This includes both meat and dairy, from all animals (ruminants).

See mathsSee maths

pasture

2.8 billion tonnes/year

Dry mass of all grass & leaves, grazed from all pasture land

Source:

Breewood, H. & Garnett, T. (2020). What is feed-food competition? (Foodsource: building blocks). Food Climate Research Network, University of Oxford.
Page 10
References primary source:
Mottet, A., de Haan, C., Falcucci, A., Tempio, G., Opio, C., & Gerber, P. (2017). Livestock: On our plates or eating at our table? A new analysis of the feed/food debate. Global Food Security.

residues

1.7 billion tonnes/year

Dry mass of all crop residues, byproducts, and oilseed cakes except for soybean

This should be, in principle, all the human-inedible parts of food crops (inedible due to being too fibrous; ruminants can digest the fiber and get calories from it).
Soybean meal is not counted here, because it can be turned into human food (soy flour).

Source:
Breewood, H. & Garnett, T. (2020). What is feed-food competition? (Foodsource: building blocks). Food Climate Research Network, University of Oxford.
Page 10
References primary source:
Mottet, A., de Haan, C., Falcucci, A., Tempio, G., Opio, C., & Gerber, P. (2017). Livestock: On our plates or eating at our table? A new analysis of the feed/food debate. Global Food Security.

conversion_ratio

133

Ruminants produce 1 gram of human-edible protein for every 133 grams of dry matter they eat.

Dry matter includes all materials eaten by ruminants (both human-edible and human-inedible).

Source:
Mottet, A., de Haan, C., Falcucci, A., Tempio, G., Opio, C., & Gerber, P. (2017). Livestock: On our plates or eating at our table? A new analysis of the feed/food debate. Global Food Security.
The number is mentioned in the Abstract: https://www.tabledebates.org/research-library/livestock-our-plates-or-eating-our-table

world.population

8 billion

(pasture + residues) / conversion_ratio (grams/day per capita)(world.population) (calculation loading) ^ Total amount of protein from both meat and dairy, combined. iThis is probably a slight overestimate, because feed efficiency ratios tend to be lower when cows are fed less grain.

This is less than the status quo, because the animals wouldn't be fed corn grain or soybean meal(...)( nor anything else that could have been turned into food for humans. Corn grain can be ground into corn flour (for tortillas etc) and soybean meal can be ground into soy flour and used in baked goods to improve protein & texture. It can also be used for making soy protein isolate (supplements, imitation meats, etc). ).

Status quo

Ruminants (cows, buffalo, goats and sheep) produce a total of about 16 g/day of protein per capita globally.

• 10 g/day protein from milk(...)( from 297 mL/day of milk ) per capita
• 6 g/day protein from meat(...)( from 30 g/day of meat ) per capita
• This was calculated in Code:food2.sql.

Not all of this is grass-fed. Also, grass-fed animal production can't really increase without destroying forests and other wildlife, because most of the world's farmland is already pasture, and that's not even counting rangelands which are also already grazed upon.

Total animal protein production (all animals) is about 35 g/day per capita globally. Consumption is less, because some of it goes to waste.^{[QUANTIFICATION needed]}

Hunting

Hunter-gatherer lifestyles were sustainable in prehistoric times when the world population was less than 0.1 billion - today we are at 8.0 billion. Hunting might be a great survival tactic if you're lost in the woods. But it's not going to feed the world. There would be mass extinctions of wild animals if we tried.

Fishing

Wild-caught fish could provide 5 or 6 grams/day of protein per capita globally, if none of it was wasted.

See mathsSee maths

seafood.production.wild

93 million tonnes/year

Global production of wild-caught fish and other seafood (not farmed)

Includes bones.
Using most recent data available.
Fishing grew a lot from 1960 to 1990 but (unlike fish farming) has not increased since 1995. This suggests that we've reached the ecological limit.

https://ourworldindata.org/fish-and-overfishing

fish.protein

18%

Protein content of fish (divided by total mass including bones)

world.population

8 billion

Number of people alive today, globally

https://www.unfpa.org/data/world-population-dashboard
Last updated in 2023

Grams of fish: seafood.production.wild (g/day per capita)(world.population) (calculation loading) Grams of protein: seafood.production.wild * fish.protein (g/day per capita)(world.population) (calculation loading)

The sustainable level of consumption might be a bit less than this, because overfishing is still an issue.

The rest of fish is farmed, which, as mentioned earlier, is a net loss of protein. Farmed fish are fed food crops that humans could otherwise eat.

FAQ

What about chickens & pigs?

Since chickens & pigs are not ruminants, they depend on eating grains or other foods that people could eat - this includes the "table scraps" often mentioned by owners of chickens.(...)( To see how to really use vegetables to the fullest, see food/full_use#vegetables. )

Backyard chickens can't solve the food-inefficiency problem, but they can at least reduce the animal cruelty problem. Backyard chickens are generally treated better(...)( with some exceptions, unfortunately ) than chickens in factory farms. Also, chickens are useful on crop lands because they can eat insects that would otherwise be pests.(...)( This can help with crop yields. Chickens also poop which can help fertilize the soil, but from a higher perspective, this doesn't add any minerals that weren't already there in the first place (the soil page will explain this in more detail). ) This could certainly contribute some chicken & eggs to the food supply, but it probably wouldn't be much compared to the status quo of chicken consumption.^{[QUANTIFICATION needed and could be added to the total]} To be fair, when it comes to exceeding the "limits to sustainable animal consumption", chicken isn't as bad as beef(...)( for the same amount of meat ). Cows have a much worse feed efficiency, which is a problem when they are fed grains.

Writer's comments

This page mostly deals with the inefficiency problems in agriculture. It doesn't account for other environmental issues such as methane emissions or soil depletion, or other ethical issues like animal cruelty(...)( On one hand, at least grass-fed cows aren't forced to spend their whole lives in cages. On the other hand, male calves are almost always separated from their mothers at birth and slaughtered for veal, since they aren't very useful to the milk or beef industry (only a small number of bulls are ever needed). This is obviously distressing for the cows whose sons are taken away and killed. There needs to be a page on this. It could talk about whether there are any less-cruel alternatives (sex-selective abortion, perhaps? would the cost be reasonable though?). ). Maybe this page should be a subpage, and there could be other subpages involving those issues. The main "Limits to sustainable animal consumption" page could provide just a summary (tl;dr) and links to all the subpages.

See also

• Food - main topic
• Food/faq - to answer questions such as "if we ate less meat, what would happen to existing farm animals?"
• Plant-based food, which can provide the rest of dietary protein & calories.