How frequently should one fast?
The New Testament does not give guidelines for how frequently one should fast. The Pharisee in Luke 18:11-12 fasted twice a week. By the time of Christ, the Pharisees had turned fasts into legal bondage. The best advice is found in Galatians 5:18: “But if ye be led of the Spirit, ye are not under the law.” We need to be led by the Spirit in how often we fast. There is a danger that a spiritual observance done regularly can become a form or ritual without true spirituality. Fasting, whether regular or occasional, is a personal decision between an individual and God. Some people have broken their health because they fasted too frequently and too long. This is not temperate and is not caring for the body as the temple of God.
It is also important to actively seek the Lord in fasting and not ignore its value and necessity. Jesus said His disciples would fast, which means if we are His disciples, we should be fasting. Some fasts will be based upon the need of the moment. There is also value in setting aside a time of week or month to exercise spiritual discipline and consecrate it to the Lord in fasting and prayer.
What type of fast should be observed and for how long?
This is another decision between an individual and God, for fasting is a voluntary gift. Whether a normal fast, a total fast, or a partial fast, all is to be done as inspired by the Spirit for the glory of God. The length of fasting is also dependent upon the leadings of the Lord. Moses, Elijah, and Jesus were recorded as fasting for forty days, but some of this was supernatural and would be rare for the general populace. A lengthy fast is to be entered into carefully and with regard to one’s physical health.
The king fasted for Daniel one night (Daniel 6:18) as that was the specific time of need. Esther had the Jews fast for three days and nights (Esther 4:16). The average fast in the scripture as practiced by the Jews was often one day from sunrise to sunset (Judges 20:26, 2 Samuel 3:35) with a meal eaten in the late evening. Some fasts were 24 hours from sunset to sunset. There are times that someone might fast for even one meal to take special time with the Lord.
Fasting is about laying aside earthly food to partake of the spiritual. It is of little value to lay aside a meal to then eat a larger portion on the next meal. The important thing is that the spirit connects with the Lord. Fasting should be appointed by God to honor and glorify Him and designed to accomplish His sovereign will.