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.
Dr. Shew says of the first few days of fasting: "A feverish excitement of the system, together with a feeling of debility, faintness and depression is generally experienced. The patient becomes discouraged and melancholic, and is very excitable and sensitive to surrounding influences. He also experiences pains and soreness in the loins, feet, and sometimes in the joints. He becomes very tired of the sitting posture and leans to one side or the other for support. But all of these disagreeable symptoms, which are necessary in the process, grow by degrees less and less, as the morbid matter is eliminated from the vital economy. And when the body has at last grown pure, these unpleasant consequences disappear entirely, and the convalescent gains strength with inconceivable swiftness through the period of the after-care."--The Hydropathic Family Physician, p, 790.
As we almost never meet with fasters who present the picture here drawn by Dr. Shew, I am of the opinion that his description is a good index to the grossness of living habits of the people of his time. When we consider that the symptoms presented by the faster are in keeping with the unphysiological character of his mode of living, this seems to me to be a fair conclusion. Great changes for the better have taken place in our living habits during the hundred years that have elapsed since Shew wrote the foregoing lines. Any of the symptoms he enumerates may be met with, but we almost never see all of them in a single patient. Many patients never develop any of them.
The first two days of the fast are usually the hardest, due (1) to the persistence of the demand for food, and (2) to the sudden withdrawal of the accustomed stimulation. Headache, dizziness upon arising, spots before the eyes, nausea, vomiting and gnawing, or an "all-gone" sensation in the stomach, are the chief elements of discomfort during the first few days of the fast. These symptoms are largely the result of the withdrawal of coffee, tea, tobacco, condiments and stimulating foods. Fat people and "good livers," suffer most in these respects. As a general rule, it may be set down that the more marked these symptoms are during the early days of the fast, the sooner the fast will accomplish the desired results.
I do not think that it can be too strongly emphasized that the bodily sensations of fasting are, in many cases, more pleasant than the bodily sensations of feasting. The patient who has suffered so much previously from being forced to eat when there was no desire for food, the patient who has suffered so much pain after all food, is likely to feel a great sense of relief and satisfaction from the time the fast begins.