If "my flesh is real food" was a metaphor, why did many of Jesus' disciples desert him?

We are to accept Him as that sacrifice for our atonement. These disciples didn't understand that and took it as literally eating His Body and drinking His Blood. Remember the night of the Passover where He broke the bread and poured the wine and told them what that stood for. He told them to do this often so that they could be reminded of what He'd done for them all.