Fast is derived from the Anglo-Saxon word, faest, which means "firm" or "fixed." The practice of going without food at certain times was called fasting, from the Anglo-Saxon, faesten, to hold oneself from food. Like most English words, the word fasting has more than one meaning. Thus, the dictionary defines fasting as "abstinence from food, partial or total, or from proscribed kinds of foods." In most religious fasts abstinence from proscribed foods is all that is meant. We may define it thus: Fasting--is abstention, entirely or in part, and for longer or shorter periods of time, from food and drink or from food alone.
From Dr. Herbert Shelton's The Hygienic System Vol. III: Fasting and Sun Bathing
