Well, stinky, i think (i may be wrong, though) that fasting is more an way for exercising control over your desires.
As many things called "sins", or things that are wrong, are manifestations of our desires, i think if you are a truly spiritual person, you must have control over them.
And, sincerely, controling your stomach when you are hungry is a HARD work... if you can do it sucessfully, then probably you can control most of your desires also, as usually they are less "tangible", less "real" than the burning feeling of hunger in your stomach.