One of the things that constantly surpises me, is how powerful something like fasting has shown itself to be to effect change in my spiritual walk.  One of the most challenging things a Christian must do is put down their flesh.  There are few instances where I don’t know the right thing to do in a situation, but many where I struggle with whether or not I am willing to do it.  I find that when my flesh rises up to a point where I am doing things I know are sinful and things I am not wanting to do, that fasting has a powerful impact on my desire to do what it right.  You might ask, “How do I work up the willpower to do that, if I can’t will myself to not sin?”  That is a good question, and the way I generally start is by telling myself I am going to fast for a day.  Then I set a date for it.  Then I hold to it.  If I don’t hold to it, I set another date, and maybe tell a spiritual confidant about it and to help hold me to do it.  Knowing the change it brings about has always been a motivation for me.  When I fast for one day, I generally only drink water, but fruit juice is also okay, escpecially for extended fasts.  Instead of eating, at the times I would normally eat, I spend that time seeking God.  Also, I refrain from watching any TV or reading anything that would excite the flesh.  I try to focus on God the whole day.  It does something to me that tends to diminish the hold the flesh has on me, and then I feel more freed up to be more self-disciplined in other areas of my life.  Fasting is like the nuclear weapon of spiritual warfare.  It has great power to bring our flesh under submission.

Mark 9:29
And he said unto them, This kind can come forth by nothing, but by prayer and fasting.