VEGANS are good for the environment. Growing their food requires less land than raising meat does. Animals do not turn all the energy in the crops they eat into calories in their muscles. They need some of that energy to stay alive—and while that overhead is good for the animals, from a food-production standpoint it looks like a waste. This waste means you need more land per calorie of food if you are producing beef than if you are producing broccoli. Admittedly, a lot of grazing is on land that would not necessarily be suitable for arable farming. But the finding from the UN’s Food and Agriculture Organisation that raising livestock takes about 80% of all agricultural land and produces just 18% of the world’s calories is still telling.

Alon Shepon of the Weizmann Institute and colleagues have looked at this in terms of opportunity costs. Choosing to make a gram of protein by feeding an egg-laying hen, rather than getting the equivalent of a gram of egg protein from plants, has an opportunity cost of 40%. Getting the gram of protein from beef represents an opportunity cost of 96%. They argue that if America stopped paying these opportunity costs and got the protein from plants in the first place, it would be equivalent to increasing the food supply by a third—or eliminating all of the losses due to food waste.

Read more in our briefing, The retreat from meat