I've been thinking about trying fasting myself. I used to fast occasionally a long time ago, and it seemed as though my stomach would always shrink a little, and things would basically tighten up around my gut. And I'm thinking that might not be a bad thing. I had always heard that fasting gave your digestive organs a rest and an opportunity to heal. I wonder about the acid production though.
Having said that, fasting can do more harm than good if not done properly. The biggest risk seems to be setting up a sense of deprivation that results in overeating or bingeing at the conclusion of the fast. I think if you are going to fast you need to have a precise plan for the transition from fasting to normal eating again. For instance if you're going to fast for three days, plan for a gradual return to a normal diet for three more days. Therefore, it's a six day process (and discipline), not just three. It's better to do a shorter fast with a good transition than a longer one that leads to bingeing that ultimately does more harm than good. Other alternatives are doing some sort of a simplified diet, such as just brown rice, steamed vegetables, fruits or juices. The book 'Healing with Whole Foods' by Paul Pitchford has an excellent section on therapeutic fasting.
In general making gradual changes in diet (and meal size) over time may be more effective than the all or nothing approach of fasting. Fasting can be a powerful tool, but it can be difficult and somewhat dangerous in terms of setting up cycles of deprivation and overindulgence that can lead to disordered eating. The author Geneen Roth always says 'behind every period of deprivation lurks an equal and opposite binge.' There are some people who can fast successfully and some for whom a more gradual approach is better.
I hope this helps. Good luck.