This is the only record we have of any of Christ’s followers forsaking him for purely doctrinal reasons. If it had all been a misunderstanding, if they erred in taking a metaphor in a literal sense, why didn’t he call them back and straighten things out? Both the Jews, who were suspicious of him, and his disciples, who had accepted everything up to this point, would have remained with him had he said he was speaking only symbolically. 

But there is a problem with that interpretation. As Fr. John A. O’Brien explains, "The phrase ‘to eat the flesh and drink the blood,’ when used figuratively among the Jews, as among the Arabs of today, meant to inflict upon a person some serious injury, especially by calumny or by false accusation. To interpret the phrase figuratively then would be to make our Lord promise life everlasting to the culprit for slandering and hating him, which would reduce the whole passage to utter nonsense" (O’Brien, The Faith of Millions, 215). For an example of this use, see Micah 3:3.

"The words I have spoken to you are spirit" does not mean "What I have just said is symbolic." The word "spirit" is never used that way in the Bible. The line means that what Christ has said will be understood only through faith; only by the power of the Spirit and the drawing of the Father (cf. John 6:37, 44–45, 65).