Could a plant-based diet feed the world?

The objection

“It’s a nice idea, but you can’t feed eight billion people on plants. We’d starve.”

The answer

The fear assumes plant foods would have to be grown on top of everything we grow now. More than a third of the world’s crop calories already go into animal feed, though, and only a small fraction of them come back as food [1], so a diet built on plants needs less cropland than the one most of the world eats today [2].

Poore and Nemecek’s data from about 38,700 farms in 119 countries (2018) show meat, farmed fish, eggs and dairy using about 83% of the world’s farmland while providing 37% of its protein and 18% of its calories, and in their model a diet without animal products cuts food’s land use by 76% and its arable land by 19% [2]. Cropland for human food would grow, but the cropland for feed would shrink by more [5]. How much land that would free, and what it could become, is covered in what would happen to the farmland if everyone went vegan.

Do we already grow enough to feed everyone on plants?

The crops the world already grows could feed the 9.7 billion people expected by 2050, according to an analysis of global food supply by Berners-Lee and colleagues (2018), as long as most meat and dairy gave way to plant foods and far more people could get food [3]. They followed calories, protein, vitamin A, iron and zinc from the field to the plate, and found no nutritional case for feeding animals crops that people could eat, since doing so shrinks the supply of calories and protein [3]. Their conditions are demanding: people would have to eat more of the crops now fed to animals, maize especially, and getting food to everyone would take very large changes in the economic and social circumstances of many [3]. If diets keep moving towards more meat, fish and dairy, as projections by the UN’s Food and Agriculture Organization (FAO) suggest, and waste isn’t cut, the world would need 119% more edible crops by 2050 [3][7].

Vitamin B12 wasn’t among the nutrients they followed, and plants don’t supply it anywhere, so on a plant-based diet it has to come from fortified foods or supplements [5][6]. Researchers at the FAO (2017) add that in some places vitamin A, iron and zinc can be hard to get in sufficient amounts from plant foods alone, and that for many households livestock mean manure, draught power and income as well as food [4].

How much food is lost by feeding crops to animals?

Most of the calories fed to animals are lost: Cassidy and colleagues (2013) found that 36% of the calories from the world’s crops went to animal feed and only 12% of those came back as food [1]. For every 100 calories of crop feed, they estimated about 40 return as milk, 22 as eggs, 12 as chicken, 10 as pork and 3 as beef, figures that leave out grazing and cover only beef from feedlots and mixed crop and livestock farms [1]. Their figures were averages for 1997 to 2003, and an FAO team (2017) found that livestock still ate about a third of the world’s cereal production in 2010 [4]. In principle, Cassidy’s team calculated, growing crops only for people to eat, instead of for animal feed, biofuels and other industrial uses, could raise the calories available by as much as 70%, enough for about 4 billion more people before any waste [1]. The mix of crops would have to change as well, because feed cereals passed straight to people wouldn’t give them proper nutrition [5].

The same FAO team found that 86% of what livestock eat, by dry weight, is material people don’t currently eat, mostly grass, leaves and crop residues, and that about 1.3 billion hectares of the grassland used by livestock could not be turned into cropland [4]. Even on their count, a kilogram of boneless meat took 2.8kg of human-edible feed in ruminants such as cattle and sheep and 3.2kg in pigs and poultry [4]. Land that can only be grazed is covered in the answer on whether farming needs animals.