Excessive protein consumption is now strongly linked to bone weakness and osteoporosis. Studies done on calcium loss have shown that as protein consumption increases, so does calcium loss. So for preventing calcium loss and the possibility of osteoporosis, plant protein is superior to animal protein. The whole idea that this is necessary is a myth. It's good to get a variety of foods, because you need all the various vitamins and minerals - not because of protein.
Protein is one of the easiest nutrients to get.