> about a factor of 10 more is the usual rule of thumb
That's often a dishonest figure which ignores how land is actually used, such as:
- Much of the land used for animals (for grazing etc) is not suitable for growing human edible plants.
- We feed animals with plants that would otherwise go to waste. When growing corn, we only use the seeds. The whole rest of the plant (i.e. most of it) is feed to animals.
> Much of the land used for animals (for grazing etc) is not suitable for growing human edible plants.
I wasn't talking about land use. I was talking about energy. Plants capture solar energy directly. Animals capture it indirectly, by eating plants. That extra stage in the food chain decreases the available energy to humans eating animals instead of plants by a factor of about 10.
Also, if plant protein largely replaced animal protein in human diets, the land now used for animal grazing could be used for wild animals that weren't raised for food at all but just allowed to exist in their natural habitat. So the fact that that land is not suitable for growing human edible plants does not mean the use of that land is irrelevant to the choice between animal and plant protein in human diets.
> We feed animals with plants that would otherwise go to waste.
No, they would otherwise go into the food chain somewhere else, most likely by being eaten by microorganisms and fungi. That's not "waste". It's a natural part of the cycle. Whether or not animals eating the plant material is a stage in the cycle does not change the fact that the cycle is there.
That's often a dishonest figure which ignores how land is actually used, such as:
- Much of the land used for animals (for grazing etc) is not suitable for growing human edible plants.
- We feed animals with plants that would otherwise go to waste. When growing corn, we only use the seeds. The whole rest of the plant (i.e. most of it) is feed to animals.