This was my response when David Brin made the religious argument: monastic or hermit diets are not famous for their variety or density, and one of the most common religious strictures is no meat—which immediately makes protein difficult to obtain.
Getting adequate complete protein on a vegetarian diet is not at all difficult, and in fact, usually does not even require attentiveness to one’s food intake. Getting adequate protein on a strictly vegan diet generally does require attention to one’s food intake, but is still entirely practical.
I’m sure it’s doable. That doesn’t mean it’s done. As I pointed out, on the occasions that I’ve read of historical monastic diets, especially Buddhist ones, they did not strike me as paying any attention to protein.
Getting adequate complete protein on a vegetarian diet is not at all difficult, and in fact, usually does not even require attentiveness to one’s food intake. Getting adequate protein on a strictly vegan diet generally does require attention to one’s food intake, but is still entirely practical.
I’m sure it’s doable. That doesn’t mean it’s done. As I pointed out, on the occasions that I’ve read of historical monastic diets, especially Buddhist ones, they did not strike me as paying any attention to protein.