Part of what we eat are proteins,
and our body is in part build of proteins.
Are the proteins of the body build based on proteins in food at all?
Are proteins in food directly reused in the body, or are proteins first disassembled?
How far are they disassembled, randomly in various pieces, or systematically to keep what can optimally be used to build new proteins, while nothing is wasted for energy?
(The question Can proteins/peptides pass through the intestine? and it's answers are related, and provide some context and relevant parts, but is not a duplicate.)