Augustine of Hippo

The nourishment of the body being first changed into corruption, that is, having lost its proper form, is absorbed into the substance of the limbs, and repairs their waste, passing through a medium into another form, and by the spontaneous motion of the parts is so separated, that such portions as are adapted for the purpose are taken up into the structure of this fair visible, while such as are unfit are rejected through their own passages. …

Catena Aurea by Aquinas ↗

Jerome

Do you not understand that everything that enters the mouth goes into the stomach and is expelled into the sewer? But the things that come out of the mouth come from the heart, and those defile a person. All the passages of the Gospels among heretics and evil-doers are full of scandals. …

Commentary on Matthew ↗

Thomas Aquinas

Consequently he explains. And first he explains what he had said, namely that which enters the mouth; second, what he had said, namely but what comes out of the mouth, this defiles a man; third, he draws the conclusion. He says therefore do you not understand that whatsoever enters the mouth goes into the belly, and is cast out into the drain? And why does the Lord speak thus? Chrysostom says that he speaks to them as those accustomed to the observances of the law. …

Commentary on Matthew ↗