REMEMBER if you are fasting for the first time, start out with the Normal Fast (indicated below).
You should read your Bible & pray to replace Breakfast, Lunch & Dinner. This is something necessary to help you overcome any physical hunger with God and His Word. For the Bible tells us He IS the Bread of Life! His Holy Spirit is refered to as the New Wine! And He told us if any man thirsts that He will give them drink of the Waters of Life "LIVING Water"! And ... if you are married, the Bible ALSO tells us to not have marital relations (in so many words) until we bring ourselves together AFTER the fast. It is not that sex is unholy, it is that if we are having sex during a fast, we are consentrating on our mate at that time instead of God. In a fast you are suppose to be thinking on God alone, not enjoyment of marital relations.
Futhermore, we are to wash our faces, dress as we would any other day, and not look pitiful to others. We are to not tell others we are fasting, unless of course they are fasting with us, or are our mate. This is because God does not want us to fast and put on a show. He wants us to fast and not let others know, this way we are drawing closer to Him and not trying to impress man.
The Normal Fast: There are very few rules when it comes to fasting. What you do is really between you and the Lord. There is only one fast command in the Bible and that was the fast on the Day of Atonement. This fast was from sunset of one day to sunset of the next (Leviticus 16:29;23:32). Since, people usually don't eat during the night that makes the fast fairly easy, since you can eat again in the evening before retiring to bed. According to the Zondervan Pictorial Encyclopedia of the Bible: "The rabbis ruled that one could not eat a quantity as large as a date on this day...According to the Mishna, Yoma 8:1, on the Day of Atonement it is forbidden to eat, or drink, or bathe, or anoint oneself, or wear sandals, or to indulge in conjugal intercourse" (Zondervan Encyclopedia, vol 2, 502). Of course, this direction is not from the Bible, but perhaps we can look at that as a template for a "normal fast." So in this type of fast the person abstained from food and liquid for a period of one day (from sunset to sunset). This is a normal fast.
The Partial Fast: In this type of fast, the emphasis is placed on restriction of diet, rather than abstaining completely from eating. Examples are: Daniel, Shadrack, Meshach and Abednego eating only vegetables and drinking only water (Daniel 1:15) and later on when Daniel alone practiced a limited diet for three weeks (Daniel 10:3). Some people would argue that this isn't really a fast at all, but Daniel 10:3 does use the word "mourned" which is a Biblical occasion for fasting (see below) and a common synonym for fasting.
The Radical Fast: This type of fast is one in which the person refrains from both food and water OR simply food (but not water) for an extended period of time. A radical fast can be harmful to your health and in most cases should not exceed three days. An example of a radical fast can be found with Esther and her household. Esther decided to fast for three days abstaining from both "food and water" both "day and night" (Esther 4:15-16). The rabbi Ezra and the apostle Paul also went without food and water for three days (Ezra 10:6-9; Acts 9:9). David is another example of a radical fast. He went seven days without food (but probably with liquid) as a plea to God to save the life of his child (2 Samuel 12:15-20). Fasts that extend beyond three or seven days can be found in the Bible, but these exceptions were based upon direct guidance from God or a supernatural ability given by God to complete the fast. Examples of these extreme fasts are: Moses (Deuteronomy 9:9-18 and Exodus 34:28); Elijah (1 Kings 19:8); and Jesus (Matthew 4:1-11).
Fasting is Assumed by the New Testament: When Jesus spoke about fasting, he didn't say if you fast, but "when you fast" (Matthew 6:16). Our Lord assumes that Christians will fast. And from the rest of the books in the New Testament we know that they did.
There once was an inappropriate time for fasting though: when our Lord was here on earth. During that time Jesus' disciples never fasted and that seemed unusual to the religious leaders and John the Baptist's friends. "Then the followers of John came to Jesus and said, 'Why do we and the Pharisees often fast for a certain time, but your followers don't?' Jesus answered, 'The friends of the bridegroom are not sad while he is with them. But the time will come when the bridegroom will be taken from them, and then they will fast.'" (Matthew 9:14-15).
Now Jesus is no longer physically present with us. He will not be until His second coming. So until the rapture, our Lord knows there will be times when fasting is an appropriate response. He is not here and because of that there will be spiritual struggle, and tribulation, and a need to fast.
The Occasion for a Fast is Voluntary: Fasting was looked upon as a very great virtue in the early church. In fact, they thought so highly of fasting that they inserted the term "fasting" into the Biblical text even though it wasn't in the original manuscripts (check various translations or margin notes for Matthew 17:21; Mark 9:29; Acts 10:30; 1 Corinthians 7:5)! This emphasis upon fasting also caused them to do the very thing the Pharisees had done, which was to prescribe certain set times for fasting: twice a week on Wednesday and Friday!
We need to be careful to avoid pitfalls of legalism like this. Surprisingly, a particular day for fasting was commanded in Scripture only once -- on the Day of Atonement (Leviticus 16). The fast on the Day of Atonement was connected with a deep mournful spirit in confessing sin. Now in the New Covenant, Jesus Christ has become our atonement offering, so we no longer even need to observe the Leviticus 16 Day of Atonement! In all the rest of the Bible there are no other Scriptures which command fasting at a specific time or on a specific occasion! None!
So when should a Christian fast? When he or she feels the Spirit of God leading them to fast. The occasion for fasting is a totally voluntary decision. Some of the specific times when people in the Bible fasted are listed in the next section. But basically we can say a Christian may decide to fast whenever there is a spiritual concern or struggle in his or her life. Of course, there may be times when those in authority over us proclaim a fast, as was done by King Saul (1 Samuel 14:24) or Jehoshaphat (2 Chronicles 20:3). But normally and ultimately that decision is solely between us and the Lord.
The Length of a Fast is Voluntary: When we were looking at a "normal fast" (see above) we noted that a fast was usually for one day. In addition to the Day of Atonement (Leviticus 23:32) you can see examples of one day fasts in Judges 20:26; 1 Samuel 14:24; 2 Samuel 1:12; and 2 Samuel 3:35. The Jewish day was counted from sunset to sunset, so this meant that the fast would be broken (that is, food could be eaten) after sundown. However, some fasts were longer. The fast of Esther continued 3 days, both day and night. At the burial of Saul the fast was seven days (1 Samuel 31:13) and David also fasted seven days when his child was ill (2 Samuel 12:16-18). The longest fasts we find in the Bible are for forty days: Moses (3 times -- Deuteronomy 9:9,18; Exodus 34:28), Elijah (once -- 1 Kings 19:8), and Jesus (once -- Matthew 4:2). The Biblical principle here is that the length of time you fast is determined by your own desires and the occasion or purpose of the fast. The duration can be that which the individual or group feels led to set. There is a great deal of freedom in the Lord here. However, the more common practice of a "normal fast" appears to be one day.
How You Spend Your Time While Fasting is a Personal Decision Too: My ideas about fasting were shaped more by what my mother did when I was young, and what I saw in the family than by the media or a church group. In the Bible, fasting often occurs as something you do while carrying on your everyday activities! My mother use to fast her food [but not liquids] when I was young, for various reasons. She would study the Word & pray when she fasted, and my mother ALWAYS got results. Her normal fast would be 3 to 5 days straight.
Matthew 6:16-18 demonstrates this, since Jesus pictures a situation in which Christians are among other people going about their normal duties and activities. In fact, soldiers involved in the activity of warfare sometimes fasted (1 Samuel 14:24) as well as the sailors on the ship with Paul (Acts 27:33). There is a certain sense in which fasting, even in the midst of your daily activities, becomes a constant prayer to the Lord. And in the actual experience of fasting, a periodic pang of hunger can become a good reminder to send up a short "arrow prayer" for the particular thing about which you are fasting.
What a marvelous freedom God gives us in the area of fasting. Jesus assumes that we will fast, yet he leaves the choice of when to fast, the length of our fast, and the decision of how we will spend our time while fasting completely up to us!
Fasting Does Not Negate Our Responsibility to be Obedient to God: We cannot fast and pray expecting God to bless when there is known sin in our lives. Fasting does not impress God with our spirituality to the point that he ignores our disobedience. On the contrary, genuine fasting will always cause us to examine our hearts to make sure everything is right with Him.
The people of Isaiah's day thought that they could fast in disobedience and God would hear them. But God said, "on the day of your fasting, you do as you please and exploit all your workers. Your fasting ends in quarreling and strife and in striking each other with wicked fists. You cannot fast as you do today and expect your voice to be heard on high". (Isaiah 58:3b-4).