Some Christians have unfortunately made a religion out of fasting, giving it the dominant place in their Christian life. There is, however, not a single reference to fasting in the New Testament epistles. There are no instructions given to believers on how or when to fast. There is no encouragement given to fast. This shows us that fasting is not a major aspect of following Jesus.
In the Old Testament, fasting is mentioned more often. It was most often associated with either times of mourning, such as in connection with someone’s death or a time of repentance, or with fervent prayer during times of national or personal crises (see Judg. 20:24-28; 1 Sam. 1:7-8; 7:1-6; 31:11-13; 2 Sam. 1:12; 12:15-23; 1 Kin. 21:20-29; 2 Chron. 20:1-3; Ezra 8:21-23; 10:1-6; Neh. 1:1-4; 9:1-2; Est. 4:1-3, 15-17; Ps. 35:13-14; 69:10; Is. 58:1-7; Dan. 6:16-18; 9:1-3; Joel 1:13-14; 2:12-17; Jonah 3:4-10; Zech. 7:4-5). These, I believe, remain valid reasons for fasting today.
The Old Testament also teaches that devotion to fasting at the neglect of obedience to more important commandments, such as caring for the poor, is unbalanced (see Is. 58:1-12; Zech. 7:1-14).
Jesus certainly cannot be accused of overly promoting fasting. He was accused by the Pharisees of not practicing it (see Matt. 9:14-15). He chided them for placing it above more important spiritual matters (see Matt. 23:23; Luke 18:9-12).
On the other hand, Jesus did speak of fasting to His followers during His Sermon on the Mount. He instructed them to fast for the right reasons, indicating that He anticipated His followers would fast at times. He also promised them that God would reward them for their fasting. He Himself practiced fasting to some extent (see Matt. 17:21). And He said that the time would come when His disciples would fast, when He was taken from them (see Luke 5:34-35).
 The only exception would be Paul’s mentioning of fasting by married couples in 1 Cor. 7:5, but among English translations of the Bible this is found only in the King James Version. Involuntary fasting is mentioned Acts 27:21, 33-34, 1 Cor. 4:11 and 2 Cor. 6:5; 11:27. These were fasts done not for spiritual purposes however, but only because of trying circumstances or because no food was available to eat.