This is a wonderful overview from the natural hygienic point of view http://www.rawfoodexplained.com/introduction-to-fasting/
My purpose for the fast, starting tomorrow is to heal myself of chronic fatigue, probably adrenal related, so I will try to rest as much as possible with eyes closed to preserve nerve energy. I have till January 21st before I have to go back to school and work so I am hoping to take the whole time and see if the tongue will become pink and healthy and hunger returns naturally before breaking the fast. If it is not enough time I will do a few shorter 4 day fasts throughout the year and perhaps a longer one in the summer. I am going to try to rest the first week back to eating as well.
I am also hoping this will encourage me to eat enough fruit and greens because that has been my biggest problem with 811 so far not being able to get enough calories and nutrients in each day. In the past I have noticed that you cannot trick the body after a fast. it is a natural inclination to "overeat" and make up for missing meals the first week back no matter how you try to force yourself not to. So this will be ideal to "overeat" on fruits and greens and will be good practice in eating an ordinary normal amount of whole foods for a primate.