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.
After this survey of the many and varied conditions under which animals fast, and the different uses to which fasting is put, it becomes obvious that fasting is one of the most common phenomena in nature. It is second only to feeding and reproduction, with both of which phenomena it is allied, in importance and in breadth of application.
Fasting under so many different conditions is so common in nature and is employed as a means of meeting so many of the exigencies of life that I am forced to wonder why anyone is afraid to fast and why anyone should doubt its naturalness and helpfulness. It is one of nature's best established methods of dealing with certain physiological problems. The hibernating bear, the aestivating alligator, the sick elephant, the wounded dog--these all fast to meet the problems before them. Fasting in acute disease, when there is no digestive power, can be viewed only as a very useful means of adaptation.
As I have previously pointed out, biologically, hibernation is a means of adaptation to the conditions of winter which enables the animal to survive. The ability to go without food during this period is an important element in survival. Except for its ability to fast for extended periods, the hibernating animal would starve to death during the winter.
Our so-called scientists, sticklers as they are for classifications and minute differentiations, are still in the habit of referring to all abstinence from food as starvation. But they say of hibernation that it is a form of "starvation" that "spells survival instead of death." Strangely enough, these men refer to the abstinence of hibernation and that seen in the mating season in some animals as "physiological starvation." This is a misuse of terms. Starvation is at all times pathological, or, pathogenic.
The ability of an animal to fast, even for long periods, under many and varied conditions and circumstances of life, is a vitally important factor in survival. It is nature's best established method of dealing with certain physiological and biological problems. It may be properly regarded as a means of adjustment or adaptation--the hibernating bear, the activating alligator, the sick elephant all fasting to meet the problems before them.
If an animal can fast, it is only because it can rely upon adequate internal resources and it can afford to fast precisely in so far and so long as it duly conserves these provisions. This is the reason hibernating and activating animals function on the lowest physiological level compatible with continued life. With no physical activity and only a bare minimum of physiological activity, their internal reserves are conserved and made to last for prolonged periods--months or a year.
Salmon and the fur-seal bull do not rest and they make no effort to conserve their resources. It would be interesting to know how long these animals could fast if they ceased their activity--physical and sexual.
Fasting during the mating season probably serves some very useful purpose. We know at least, that in the case of certain very low forms of life, it restores the male after several generations of parthenogenetic reproduction. For best results, animals that fast during the mating season seem to require a reduction of surfeit. They purchase rejuvenescence by curbing their anti-symbiotic propensities and abandoning conditions of surfeit. Instability resulting from surfeit and illegitimate food can be gotten rid of and stability regained only by a return to moderation and appropriate food. For immediate results abstinence from food is essential.
Reinheimer thinks that fasting has the effect of assisting towards a re-establishment of a tolerable degree of domestic symbiosis--both for ordinary physiological, as well as for genetic purposes--in those cases where domestic symbiosis is in danger of becoming perverted by the particular organism's transgressions against the laws of biological symbiosis.
I have made no effort to exhaust the list of animals and plants that fast under conditions other than those of sickness or absence of food. The examples that have been given are sufficient to show that nature has no fear of prolonged abstinence from food and that abstinence is frequently made use of in nature, by animals in both the active and the dormant states, as a means of adapting the animal to various conditions of life, or as a means of internal alteration when this is needed. Under all conditions in which animals fast, the internal resources of the animal are drawn upon to nourish the vital tissues and carry on the indispensable functions of life.
In sickness, or when severely wounded, when no food can be digested, the organism also draws upon its internal store of supplies for these same purposes. Fever, pain, distress, inflammation suspend the secretion of the digestive juices, inhibit the muscular actions of the stomach and take away the desire for food. In such conditions there is but one source from which food can be drawn--the reserves.
In sickness, as in animals fasting through the mating period, there is much activity going on in the body. There is, therefore, much more rapid wasting of the body in these two conditions than is seen in hibernation and aestivation.
Viewing the wasted condition of animals at the end of their various fasting periods, it becomes very obvious that, while different species of animals vary in the amount of loss they can safely sustain, none of them are injured or endangered until after a large percentage of the normal weight of the body has been lost. There is, therefore, no danger in a fast of such lengths as are employed in sickness.