From Richard Foster's Celebration of Discipline:

"More than any other discipline, fasting reveals the things that control us. . . . We cover up what is inside of us with food and other things. . . . We cover up what is inside us with food and other good things, but in fasting these things surface. If pride controls us, it will be revealed almost immediately. David writes, "I humbled my soul with fasting" (Psalm 69:10). Anger, bitterness, jealousy, strife, fear--if they are within us, they will surface during fasting. At first we will rationalize that our anger is due to our hunger; then we will realize that we are angry because the spirit of anger is within us. We can rejoice in this knowledge because we know that healing is available through the power of Christ." (p. 55).