[Servant of the Cross]

Then many of his disciples who were listening said, "This saying is hard; who can accept it?" ... John 6:60

[PugetSoundSoldier]

In John 6:63 Jesus spells it out for those confused by His metaphor:

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.