"I am the Bread of Life". This seems like an odd expression. Why would God consider Himself food? Well, we need food for our life. But, Jesus is not talking about mortal life, He is talking about eternal life. In a sense, He is the Bread of Eternal Life. He is the food of eternal life.
So, is Jesus physically food or just spiritually food for us? The answer is both. We are physical and spiritual beings. Jesus is a physical and spiritual being. Jesus taught about the resurrection of which the physical was not left behind. Indeed, if the physical was not important, why would Jesus resurrect body and spirit? He even asked to eat after His resurrection to help prove He was not a ghost.
When Jesus teaches that He is the Bread of Life in John 6, He does not shy away from Him being physical food for us. When He first calls Himself the Bread of Life that came down from Heaven, the Jews start murmuring that they know His parents Mary and Joseph. Jesus then takes it a step further calling Himself the Bread of Life again, and claiming that the bread is His flesh and ‘whoever eats it will live forever’.
The Jews start quarreling about Him giving His flesh to eat. Jesus then goes another step further claiming that one needs to not only eat His flesh, but also drink His blood to have eternal life. His disciples had a hard time with this, but Jesus even asked them, “Does this shock you?” And this is the only time recorded in the Bible that any disciples left.
But Jesus was not done. He turned towards the Twelve and asked “Do you also want to leave.” It was apparent that He was serious and not backing down. Peter answered for the Twelve and they stayed with Him, but He gave them the choice to believe that He would give them His flesh and His blood for them to eat and drink.
They believed that the Eucharist was the body and blood of Christ, do we?