Christian fasting is a believer’s voluntary abstinence from food for spiritual purposes. Other types of fasting—despite the benefits they may produce for the mind and body—could not be classified as Christian fasting, and fasting by a non-Christian obtains no eternal value. It is for believers in Christ, for the Discipline must be rooted in a relationship with Christ and practiced with the desire to become more like Christ. Believers should fast according to biblical teaching and with purposes that are God-centered. It is voluntary in that fasting should not be coerced. And fasting is more than just the ultimate crash diet for the body; it is abstinence from food for spiritual purposes. There is a broader, yet often overlooked view of fasting in which, for spiritual purposes, a person abstains from or denies himself the enjoyment of something other than food. So while it’s appropriate to speak of fasting from any legitimate freedom, technically the Bible uses the term only in its primary sense, that is, abstinence from food.
To understand fasting for spiritual purposes, realize that the Bible distinguishes between several kinds of fasts.
A normal fast involves abstaining from all food, but not from water. Matthew 4:2 and Luke 4:2 say that after a forty-day fast Jesus was hungry, but they say nothing about thirst. Unless this was a supernatural fast (see below), the body can’t go forty days without water.
A partial fast is a limitation of the diet but not abstention from all food. See Daniel 1:12.
An absolute fast is the avoidance of all food and liquid, even water. See Ezra 10:6; Esther 4:16; Acts 9:9.
The Bible also describes a supernatural fast that requires God’s supernatural intervention into the bodily processes. See Deuteronomy 9:9.
A private fast is what Jesus meant in Matthew 6:16-18 when He said we should fast in a way not to be noticed by others.
Congregational fasts are the type found in Joel 2:15-16 and Acts 13:2.
The Bible also speaks of national fasts. See 2 Chronicles 20:3; Nehemiah 9:1; Esther 4:16; Jonah 3:5-8.
God established one regular fast in the Old Covenant. Every Jew was to fast on the Day of Atonement (see Leviticus 16:29-31).
Finally, the Bible mentions occasional fasts. These occur on special occasions as the need arises. Examples of these are found in 2 Chronicles 20:3, Esther 4:16, Matthew 9:15, and Acts 14:23.
Adapted from Whitney, Donald S.. Spiritual Disciplines for the Christian Life Study Guide (pp. 106-108). The Navigators.