The origins of Fasting as a Sacred Tradition
Every major religion has encouraged or required its followers to practice a form of fasting. Fasting though existed before these institutions and has older roots. Dietary restrictions, typically in the form of a taboo, were and are common among primitive peoples. Examples of not eating certain vegetables, the meat of certain animals, or refraining from eating specific foods during certain days of the year can all be found in primitive societies. Some of these taboos were for health reasons - avoiding harmful or seasonally tainted food stuffs, for example, but there are also many examples that are firmly rooted in fasting rather than safety.
Ancient fasting practices were generally motivated by two, often intertwined, reasons: special spiritual rites and purification.
Traditions often demanded a fast before an important event of undertaking. Many people fasted as part of ceremonies that initiated them into adulthood. Longer term food deprivation can lead to a person experiencing hallucinations. In the past, these fasting induced experiences were interpreted as mystical revelations. Longer term fasting rites sought to produce these kinds of effects in order to discover revelations and uncover new insights.
Coming of age rituals often included fasting and many followed a common pattern. The person coming into adulthood usually made an abrupt and symbolic break with his past. This included going through an ordeal where they are separated from their village. This symbolic break is further enhanced by fasting. Such fasts lasted from twenty-four hours to many days. Shorter fasts tended to be symbolic cleansing rites. Longer fasts were ideally accompanied by some form of spiritual experience. The ending of the fast coincided with returning home, which was often a time for a group ceremony or celebration. Fasting for initiation could also lead to additional fasting later on in life.
Tasting the first fruits of a new harvest, going on a hunt, going to war and other important and often unpredictable events were often preceded by a fast. A common reason for these practices is similar to one of our primary modern day impetuses for fasting - its role in purifying the body. This was not seen from a health perspective though but served a role in readying someone for a specific purpose, to give special thanks, or to receive a special reward.
The general idea was that when someone had denied themselves long enough they would be fit to receive or give something special as a result of their improved state. This might be a message or reward from a deity, a conferring of extra strength to help fight a battle, and so on. Ancient priests and shaman might fast to turn aside the wrath of vengeful spirits, hunters would fast to prove they deserve luck in killing their quarry, and a farmer might fast to encourage the spirits of earth and weather to send them bountiful crops.
Throughout the world of primitive man then we find there were three main motives for fasting: purity, rewards and thanks, and mysticism. The activity of fasting was a voluntary act, as opposed to going without food because none was available, and fasting often meant abstaining from all food and drink. Finally an argument can be made that fasting was the most common religious rite found among primitive cultures.