Your definition of environmental sustainability implicitly assumes a fixed, or arbitrarily bounded, population size in steady state. Whatever set of foods we ch

Your definition of environmental sustainability implicitly assumes a fixed, or arbitrarily bounded, population size in steady state. Whatever set of foods we choose to feed the population with, it is always possible (and historically has been inevitable) for the population to outgrow the available supply. Sustainability only makes sense relative to a particular population size, and so something is only unsustainable in the absolute sense if the population needed to produce it exceeds the population which can survive upon it. This is not the case with the food types you refer to, and the producer/consumer ratio is precisely the thing that we develop new technologies to reduce. If anything, I see it is better for us to engage in inefficient land use, because it provides spare capacity which can be used to mitigate prolonged disasters; a view strongly influenced by the book "The Collapse of Complex Societies", by Joseph Tainter.