In the old and new medicine, the temporary abstention from food, drink, and sex, is proved to be salutary, and useful in health of almost all. Most of the diseases are due to habitual eating and drinking to excess. All the foods eaten, are not attracted to the body. They may leave some extra fat and glucosides, and other unnecessary compounds in different organism of the body, particularly in the blood; making suitable marshy points for cultivation and development of microbes and other germs of illnesses. The FAST burns out all the rubbish, and unessential extrinsics of the body. According to a tradition; the prophet has said: ``Fast and live healthy.'' He also has said: ``The stomach is the house of all kinds of disease, and the FAST is the head of all the medicines.''