Is the First Lord's Supper a Metaphor?

There's no indication here or anywhere in church history that such a miraculous transmutation is occurring. Whoever eats my flesh and drinks my blood is eternal life, and i will raise him up at the last day. That sounds very literal. But if you read just a bit further in john six, like the next sentence, well then he goes to language that sounds more symbolic. This is jesus talking to the disciples after they're concerned by this. He says, does this offend you? What if you see the son of man ascend to where he was before? The spirit gives life. The flesh counts for nothing. The words i have spoken to you are it and they are life.