I just completed an 8 day fast. Just for fun I kept some statistics while I was on it. You can see them below.
As you can see, my weight, blood pressure, and blood glucose levels changed dramatically over the course of the fast. Eight days is not a particularly long fast, but certainly enough to demonstrate the major benefits derived from fasting. Some of those benefits are measurable but there are just as many subjective benefits which will elude you until you actually do it yourself.
There are many good books about fasting which will give you insight into the theories behind it, historical usage of fasting, methodologies, and so on. Even though I have undertaken 5 or 6 fasts and read a number of books on the subject, one of my favorites is still Joel Fuhrman's easy to read and easy to understand introduction called Fasting and Eating for Health. Listed below are a few other books about fasting and eating which I have found helpful.
Lee A. Shurie
(Note: I am not a doctor and do not dispense medical advice.
This is purely an account of my own personal experience, which
may be unique to my own body type, genetics, and lifestyle.)