St. John Chrysostom: What true fasting really is.

Do you see, dearly beloved, what true fasting really is? Let us perform this kind, and not entertain the facile notion held by many that the essence of fasting lied in going without food till evening. This is not the end in view, but that we should demonstrate, along with abstinence from good, abstinence from whatever is harmful, and should give close attention to spiritual duties. The person fasting ought be reserved, peaceful, meek, humble, indifferent to the esteem of this world. You see, just as one has neglected the soul, so it is necessary to neglect empty esteem as well, and to have regard only for Him who examines our innermost being (cf Ps 7:9) and with great care to direct prayers and confessions to God, and provide for oneself according to one's ability the help that comes from almsgiving.
+St. John Chrysostom, from Homilies on Genesis, homily 8 #15.