'Then I set my face toward the Lord God to make request by prayer and supplications, with fasting, sackcloth, and ashes.'
Daniel 9:3
During this phase in Daniel's life, he understood that his people were under God's chastisement. They had been exiled as predicted by God's prophet. So he interceded on behalf of his people, confessing their sins to God, and attended these prayers with fasting, sackcloth and ashes. This was Daniel's way of 'afflicting' himself before God. See especially the verses that follow.
We learn from this, and other passages on fasting, that there are appropriate times for it. In particular, we ought to fast and pray when we experience God's judgment or see a need to overcome a particular sin, personally and or nationally. (See Joel 2:12, Esth. 4:16, Matt. 9:15, 1 Cor. 7:5) Our confession of faith notes that part of the special occasions of worship includes 'solemn fastings.' (WCF 21:5) The Bible informs us that there are times which especially call for fasts: sickness (Psalms 35:13), times of death (I Samuel 31:13), times war (Judges 20:24-28), when under deep conviction of sin (Ezra 10:3), before making an important decision (Acts 13:2; 14:23), and seeking God's power to overcome oppressive spiritual forces and sin (Mark 9:28,29).
While I have not personally fasted as frequently as I ought, when I have it has never been time wasted. In fact, it has been a blessing! May it be so for those who desire to partake this coming Monday.
Along with the biblical principles of fasting, men have provided conventional wisdom with regards to the spiritual discipline. Allow me to pass along helpful guidelines.
1. Prepare for your fast. Think ahead of when, for how long, and where you will do it. If you have to work, perhaps a break or lunch time might be best. Think of a 'prayer closet' you might use for the occasion. If this will affect any medication or medical condition, it might be best to consult your physician. If you are highly dependent on certain ingredients (caffeine), you might get a headache.
2. Be prepared to read your bible. A great part of fasting is meditating on God's word and examining one's self in light of it.
3. Don't overdo it. I once tried to fast all day while working a construction job. It didn't work out well, as I began to get very hungry and needed energy for my work. So the only thing I could eat at the time was a pack of cookies. That didn't end well. If it's your first time, or you are out of practice, then maybe just skip one meal. Maybe you should only fast from foods, not liquids. Eat plenty of healthy food before your fast, not junk food.
4. Don't brag about your fasting. Jesus warns that this was the practice of the hypocritical Pharisees in his day. (Mt. 6:16)
5. Come off your fast slowly. Don't break it suddenly with steak and potatoes, unless you have a very small portion. Your stomach will need time to adjust.
6. Do it in faith! Expect and ask God for His blessing. Expect God to show you your need for repentance, and expect the Lord to shower His mercy upon our nation, for His name's sake, as you intercede for it in Jesus' name.
May the Lord use the spiritual discipline for our good and His glory! -Kevin