It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life.
Bread is the metaphor for the Spirit and teachings of Christ. Per His own words.
"As a result of this, many [of] his disciples returned to their former way of life and no longer accompanied him. Jesus then said to the Twelve, "Do you also want to leave?" John 6:66-67
Nothing in there about metaphors. If it was a metaphor, verse 66-67 would read, "hey, come back guys, I only meant this metaphorically!
Jesus said "to Thomas: 'Take your finger and examine My hands. Put your hand into My side. Do not persist in your unbelief, but believe!' ... John 20:27
Speaking of believing (and DNA testing), check this out: Eucharistic Miracle of Lanciano!
"And Mary said: 'My soul magnifies the Lord; my spirit rejoices in God my savior. For he has looked upon his handmaid's lowliness; behold, from now on will all ages called me blessed.'" ... Luke 1:46-48