According to a commentary by Thomas Aquinas, [pita] bread (and I suppose those extremely leavened (aerated) wafers) become "the indestructible flesh of God, the Son":
...The food that sustains the body is perishable, since it is converted into the nature of the body; but the food that sustains the spirit is not perishable, because it is not converted into the spirit; rather, the spirit is converted into its food. Hence Augustine says in his Confessions: “I am the food of the great; grow and you will eat me. But you will not change me into yourself, as you do bodily food, but you will be changed into me.”...
But if the flesh is indigestible, won't it end up being flushed down the toilet?:
Mark 7:19 For it doesn’t go into their heart but into their stomach, and then out of the body.” (In saying this, Jesus declared all foods clean.)
Has this been considered and addressed?