Man does not live by bread alone
Physical nourishment is not sufficient for a healthy life; man also has spiritual needs.
From the Bible, Deuteronomy 8: 2-3 (King James Version):
And he humbled thee, and suffered thee to hunger, and fed thee with manna, 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.
also in Matthew 4:4:
But he answered and said, it is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God.
and Luke 4:4:
And Jesus answered him, saying, It is written, that man shall not live by bread alone, but by every word of God.
See also: the List of Proverbs.