Benadam:
Well, what we believe is, it turns into Jesus.
But what does that mean? How do you explain this in 21st century terms? We know that its molecular composition is the same before and after the consecration, so it does not change in chemical substance. Catholics disagree with those who believe that Jesus is united to the recipient in invisible spiritual form. Catholics disagree with those who would believe that the meaning and significance of the elements of Communion change. It is not just how they are “regarded” - this would imply a symbolic change and not necessarily a “real” change. (I think of the meaning attached to a national flag vs. a pile of colored fabric. The fabric doesn’t change, but the flag is regarded to have a different meaning than the cloth scraps that fell to the floor while sewing it.)
So what "real"ly changes?
I can give it a good layman’s try.

Any way it is conceptualized with words is going to fall way short. Even the doctrine of Transubstantiation can only be a model that points the mind but in no way is able to describe the mystery.
We speak of the substance. Sub=under stance= stand. Stand-under.This is the word used to conceptualize what stands under and supports what we know by our senses. Substance doesn’t submit to our senses. Just a word to conceptualize spiritual reality. Everything we know by our senses are referred to as accidents. The accidents don’t exist in of themselves, their existence is contingent on the support of what ‘stands under’ them.
The elements, molecules, everything we can sense, these are not the substance. these are the accidents, or just the 'outer appearance.
Something like the molecules of your body now, are not the same molecules of your body when you were an infant, but both, you now, and you then are you, so, your molecules, cells and organs are not substantially you but are your accidents .What is known of you by the senses are accidents but your substance is your soul. Both are essential to your being. That is an abstraction that the human mind can grasp, and only a model to conceptualize what isn’t sensible.
That being said, in a similar way the molecules of bread are accidents, or appearance of bread. The Consecration requires that the bread be as was blessed by Christ. Bread as Jesus blessed and broke. The proper words( faithful to the memory of Jesus words) and the proper person(in persona Christi) praying as Jesus did, calls the power of the Holy Spirit, as Jesus did, to change the sub-stance of bread into Jesus Christ in heaven… We believe that the substance has changed and the accidents remain. .