fasting is simply giving up something that you have for a period of time for spiritual growth. I used to be catholic, and i do remember (even tho i was 6) that for a week before Easter, we would fast meat, or something.. I think, maybe i don't remember too well? but yes it is Biblical: moses fasted 40 days(Deut.9:11-18), fasting in time of sorrow (1sam 31:13), during national crisis (2sam 1:12), fasting for peoples sins (ezra 10:6), in need of courage (Ester 4:16), humbled by fasting (ps. 35:13), scorn for acts of humility (ps. 69:10-11), weaknes from fasting (ps. 109:24), real meaning of fasting (isaiah 58:3-7), egypts desolation (Ezekiel 29:11-13), distraught king (dan. 6:18), prayer and fasting (daniel 9:3) fasting for repentance (joel 1:13-14), animals and men fast together (jonah 3:7), insincere fasting (zech. 7:1-6), Joyful fasting (zech. 8:19), example of Jesus (matt 4:1-2), pretense of fasting (matt 6:16), disciples did not fast (matt 9:14-15), some fast, others do not (mark2:18-20), four thousand people fasting three days (mark8:1-3), Jesus in desert (luke 4:1-2), a time to eat, to fast (luke 5:33-35), worship and fasting (acts 13:2-3), fasting with evil intent (acts 23:12-13), anxiety, lost appetite (acts 27:33-36), little value in itself (1corr. 8:8).
Fasting is Biblical, but when fasting for religion gets more important than fasting for God, you have a problem. Jesus did not fast because Paul did, Paul didn't fast because Matthew was, they all fasted because God told them to (through Jesus and in the Scripture). And I'll tell you what, there is nothing that gets God's attention quicker than fasting! If you feel dry, and you feel like God doesn't hear your prayers, fast something that you love! If you love chocolate, fast that. If you love a certain band, fast that. And if you feel oppressed, fast and pray against it! Jesus says to His disciples in Matthew 9:14-15, that the reason they could not cast out a ceratin demon, was because they had to pray AND FAST. There is power in prayer and power in fasting.
But if you aren't saved by GRACE ALONE, and don't know Christ as you personal Savior, and you have not asked Him to come into you and save you from hell, or you don't believe that He died for your sins, and rose to conquer death and make a way for you to enter with Him into heaven, all fasting is in vain. God commands us to ask forgiveness before communing with Him. Communion isn't the wine and bread, its the relationship with Jesus resembled through His blood and body. And before you enter into a fast you need to ask forgiveness for your sins (you should do this daily, if not more often), so that your fasting is not in vain before the Lord.