Gentlemen, it is here, in verse 63, that the Lord himself tells us that he is speaking in metaphor. - Please read all of the chapter in the same sitting!
That interpretation however undermines the sense of the whole passage. Christ discourses about his flesh and blood, people react in shock, then (according to your interpretation) Christ tells us his statements are all metaphorical in verse 63.
Now, following your own advice of reading the entire passage, if Christ himself confirmed the metaphorical interpretation, why in verse 66 do "many disciples" still walk away from him forever? They walked away for a *metaphor*??
They walked away because they were not his elect. - Please read John ch. 6, and you will find that Christ states that he did not lose any that the Father had given him, so if he lost these, then they were NOT his.
Verse 63 is so plain that I cannot see how you would try to squirm out from it.