No reason ?
Didn't he just request ( or whatever it is they do ) that the bread become the flesh so he could eat it ?
Are you talking about John 6? Some of Jesus' disciples took Jesus' teaching at face value and permanently left Him. Their error was not in their human reasoning, but their failure to put their trust in Jesus. The Apostles were confused, but nevertheless remained with Jesus. Peter said, "to whom can we go?" Peter didn't understand Jesus' (somewhat paradoxical) "hard saying," but put his faith in Jesus.
Transubstantiation is an interesting concept ... kind of like homeopathic medicine. You change the substance of something without changing any perceivable properties, in effect, simply redefining what the word substance means.
The term "transubstantiation" derives from the Aristotelian terms "substance" and "accident." The change in substance is not of the natural order; it's miraculous.
Given an understanding of these terms, the following becomes understandable:
The dogma of transubstantiation teaches that the whole substance of bread is changed into that of Christ’s body, and the whole substance of wine into that of his blood, leaving the accidents of bread and wine unaffected. Reason, of course, can’t prove that this happens. But it is not evidently against reason either; it is above reason. Our senses, being confined to phenomena, cannot detect the change; we know it only by faith in God’s word.Thus, transubstantiation is miraculous. The miraculous is possible for God.After the priest consecrates the bread and wine, their accidents alone remain, without inhering in any substance. They can’t inhere in the bread and wine, for these no longer exist; nor do they inhere in Christ’s body and blood, for they are not his accidents. The Catechism of the Council of Trent says: “. . . the accidents which present themselves to the eyes or other senses exist in a wonderful and ineffable manner without a subject.”5 St. Thomas Aquinas teaches that God directly sustains the quantity of bread (or wine) in being, and that the other accidents inhere in the quantity.6 For quantity is the fundamental accident: the others, such as color, exist as quantified—as having extension. There is no such thing as a non-extended color.