A really good site on fasting is www.juicefasting.org - for how to do it and the physical details - how to do it, what to expect, so forth. I find it very interesting how much easier it is to be a good Christian when my body is in good health. The easy anger is gone and things like patience, compassion, etc. become easier.

Also, Stephen Harrod Buhner's book "The Fasting Path" goes into the spiritual aspects of fasting quite a bit. He talks about the mental/emotional changes in fasting that bring us closer to God and strengthen our feelings of love and compassion to those around us.