As a newbie to fasting (I have done limited fasts in the past, but without knowing the physiological effects and optimum procedures) I found this book a very good introduction to it.
There are many websites and books on fasting, but I trusted the opinion of the author, since he is a medical doctor, and frequently gives evidence for his assertions. His medical explanations help clarify not only what is helpful and dangerous in a fast, but why. This, in my opinion, separates a credible expert from a crackpot in many fields and particularly for fasting.
Some items which may be constued as negative: this is not a step by step guide to fasting (as the author strongly reccomends medical supervision for fasts), and the author spends considerable space on his agenda about the importance of vegan dieting(though dieting is essential to a healthy fast, before and after).
This book is definitely worth the money for learning the principles of fasting.