This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
From the foregoing parts of this chapter it will be seen that fasting in man is practiced under about as wide a variety of circumstances as among the lower orders of life and for about as many purposes of adjustment and survival. Fasting is a vitally important part of man's life and, until modern times, when we have made a fetish of eating and have developed a ridiculous fear of going without food, even for a day, has played a major role in many of his activities.
It is very obvious that the ability to go for prolonged periods without food is as important a means of survival under many conditions in the life of man as it is in the lower animals. It is quite probable that primitive man was forced even more often than modern man to rely upon this ability in order to survive periods of food scarcity. In acute disease, in particular, the ability to go for prolonged periods without eating is very important in man, for the reason that he seems to suffer far more with disease than do the lower animals. In this condition, in which, as will be shown later, there is no power to digest and assimilate food, he is forced to rely upon his internal stores.
If man can fast, this is because he, like the lower forms of life, carries within himself a store of reserve food that may be utilized in cases of emergency or when raw materials are not available.