My limited experience with fasting is in general relationship to religious or spiritual practices. In some cases the period of fasting is associated with reflection and introspection of one’s life. This reflection may be accompanied with “down” times in terms of activities, which may take the form of prayer, meditation and reading holy/spiritual text. Some religious/spiritual disciplines provide exemptions from fasting if the individual is ill, young, elderly, pregnant, nursing or engaged in physical labor. Fasting times are often associated with times of the year (spring and/or fall) when environmental conditions are not at their extreme.
Pete