We not only live by bread, but by every word from the mouth of God.

If God said, it is so.

Deuteronomy 8:3 (KJV) – and he humbled thee, and suffered thee to hunger, and fed thee with man-na, which thou knewest not, neither did thy fathers know, that he might make thee know that man doth not live by bread only, but by every word that proceedeth out of the mouth of the Lord doth man live.