(Catholic perspective) Why was the Jesus body consumed at the Last Supper due to transsubstantiation was not mentioned to Thomas? My question is inspired by the top answer to this question, according to which transubstantiation (that the bread and the wine literally became the flesh and blood of Jesus) also occurred on the last supper.

I take this means that they ate of Jesus body before his crucifixion(?)

Later, after this death, he appeared to the disciples while Thomas was present, as explained in John 20:24-27:


  24 Now Thomas (also known as Didymus[a]), one of the Twelve, was not
  with the disciples when Jesus came. 25 So the other disciples told
  him, “We have seen the Lord!” But he said to them, “Unless I see the
  nail marks in his hands and put my finger where the nails were, and
  put my hand into his side, I will not believe.” 26 A week later his
  disciples were in the house again, and Thomas was with them. Though
  the doors were locked, Jesus came and stood among them and said,
  “Peace be with you!” 27 Then he said to Thomas, “Put your finger here;
  see my hands. Reach out your hand and put it into my side. Stop
  doubting and believe.”


This passage only mentions the marks from the nails and the spear wound on his side.

Question:

Would the consuming of his flesh not have left some kind of marks that he could then have been identified on?
No, one cannot change anything about Christ's body in the Holy Eucharist.
St. Thomas Aquinas addresses the question of &quot;Whether Christ's body is in this sacrament changeably?&quot; in Summa Theologica III q. 76 a. 6. By &quot;changeably&quot; (&quot;movably&quot;/mobiliter) he means not only locomotively (i.e., able to change from one position or place to another), but also that none of His body's accidents (properties, e.g., his color, stature, etc.) change. He writes (ibid. c., with a few of my modifications and parenthetical additions of the Latin):

When any thing is one, as to subject, and manifold in being, there is nothing to hinder it from being changed (moveri) in one respect, and yet to remain unchanged (immobile permanere) in another, just as it is one thing for a body to be white and another thing for it to be large; hence, it can be changed as to its whiteness and yet remain unchanged as to its magnitude. But in Christ, being in Himself (esse secundum se) and being under the sacrament (esse sub sacramento) are not the same thing, because when we say that He is under this sacrament, we express a kind of relationship to this sacrament. According to this being [i.e., according to His esse sub sacramento], then, Christ is not moved locally [i.e., from one position or place to another] of Himself, but only accidentally (per accidens, i.e., &quot;not per se&quot;), because Christ is not in this sacrament as in a place, as stated above (a. 5). But what is not in a place is not moved of itself locally, but only according to the motion of the subject in which it is.
In the same way neither is it moved (moveri) of itself according to the being which it has in this sacrament, nor by any other change (mutatione) whatever, as for instance, that it ceases to be under this sacrament: because whatever possesses unfailing existence of itself cannot be the principle of failing; but when something else fails, then it ceases to be in it; just as God, Whose existence is unfailing and immortal, ceases to be in some corruptible creature because such corruptible creature ceases to exist. And in this way, since Christ has unfailing and incorruptible being, He ceases to be under this sacrament, not because He ceases to be, nor yet by local movement of His own, as is clear from what has been said, but only by the fact that the sacramental species cease to exist.
Hence it is clear that Christ, strictly speaking is immovably (immobiliter or &quot;unchangeably&quot;) in this sacrament.