Bonhoeffer on fasting

"...The contast between our behaviour and the word of Jesus is all too painfully evident. We forget that discipleship means estrangement from the world, and we forget the real joy and freedom which are the outcome of a devout rule of life. As soon as a Christian recognizes that he has failed in his service, that his readiness has become feeble, and that he has sinned against another's life and become guilty of another's guilt, that all his joy in God has vanished and that his capacity for prayer has quite gone, it is high time for him to launch an assault upon the flesh, and prepare for better service by fasting and prayer. ...How is it possible to live the life of faith when we grow weary of prayer, when we lose our taste for reading the Bible, and when sleep, food and sensuality deprive us of the joy of communion with God?"