In the Synoptic gospels, Jesus has the bread and wine metaphor for body and blood consumption.
In the Gospel of John, Jesus says it is not a metaphor, followers are literally eating his body and blood. (In the gospel of John, the last of the four gospels, Jesus brings up literal cannibalism before the last supper. Jesus brings it up and loses followers. He says this teaching is too hard for those who do not stay with him.)
Any Israelite or any alien living among them who eats any blood—I will set my face against that person who eats blood and will cut him off from his people.
Lev. 17: 10
The agony in the garden happens after Jesus makes the bread and wine metaphor.
Jesus renounces the God of Israel, then he goes to the Garden of Gethsemane and finds the God of Israel is not on his side for him to continue living.