The word “Fast” comes from the Greek word “Nesteuo”, meaning total abstinence from all food for a certain period. From Scriptural examples, the length varies from daylight hours up to 40 days (Judg. 20:26; Ex. 34:28-30; Deut. 9:9; 1Kgs. 19:7-8; Matt. 4:2). It should be noted that Moses’ case of going without food and water for 40 days was a special one. While the body cannot do without moisture (water) for a very long time, it can go as long as 40 days or more without food, especially when one is doing it under divine guidance. It is discovered that on long fasts, hunger usually subsides by the end of the 3rd day and does not return until the stored food reserves in the tissues of the body are used up. This can take up to 40 days or more. There are cases of people who fasted for up to 90 days under some ideal conditions and survived. Aside such total fast as has been described, there is also partial fast as in the case of Daniel (Dan. 10:2-3).
Fasting is an act of self-denial, and mortification of the flesh under the hand of God. Fasting is a curb to the flesh and its desires. Private fasting is encouraged (cp.1Cor. 7:5). It makes us more lively in religious exercises.
Fasting reinforces the attitude of repentance and heart-felt confession (1Sam. 7:6; Ezr. 10:1, 6). In fasting, we humble and afflict our soul, owning our nothingness and unworthiness (1Kgs. 21:27-29; Ps. 35:13).
Sometimes when in some dire need, perplexity, fear, distress, etc, we may accompany our prayer with fasting (Ezr. 8:21-22; Esth. 4:3). During fasts (total or partial fast), our mental and spiritual faculties seem to be more alert and sensitive to the Spirit of God. Also intercession seems easier and more effective (cons. 2Sam. 12:16-23; Ps. 35:13; Neh. 1:4-11). The early Christians found fasting to be beneficial while seeking the will and direction of God (cons. Act. 13:2-3; 14:23). Paul fasted often, and so he kept under this body and brought it into subjection (1Cor. 9:27; 2Cor. 11:27).