Anytime you feel led to fast is fine as long as the reason for fasting is sincere and spiritual. There are a few days in the Hebrew calendar that are set aside as holiday fast days for those who wish to observe them. These days include:
Fast Day |
Date |
Fast of Gedaliah |
3rd of Tishri |
Day of Atonement |
10th of Tishri |
Fast of 10th of Tevet |
10th of Tevet |
Fast of Esther |
13th of Adar |
Fast of the First Born |
14th of Nissan |
Fast of the 17th of Tammuz |
17th of Tammuz |
Fast of Tisha B'av |
9th of Av |
Jewish tradition teaches that Moses ascended into heaven to receive the law on a Thursday and descended on a Monday. It became common to fast on Mondays and Thursdays. Some orthodox Jews still keep this tradition.
The reform branch of Judaism only recognizes the Day of Atonement as a fast day to be observed.(1)
Most fast days are considered minor fast days. That means the fast usually lasts from sunrise to sunset. On these days, breakfast is permitted if eaten before sunrise. The Day of Atonement fast day is different. It lasts 24 (sometimes slightly more) hours from sunset to sunset the following day. On this fast day, neither water nor food should be eaten. This is known as a total fast.
It is believed that fasting helps to humble the soul.
Sometimes when we are seeking to know God’s will, a fast that also focuses on prayer and drawing nearer to God can help. A fast that is not accompanied with prayer and/or the desire to know God’s will is simply a diet.
Fasting is a way to learn control over our bodies (self) instead of our bodies controlling us.
There is an interesting rabbinic comment that equates fasting with the offering of sacrifices upon the altar.
Rav Sheshet said: “Sovereign of the universe, it is known to thee that when the temple was in existence, if a man sinned he would bring a sacrifice of which only the fat and blood were offered up, and he would be granted atonement. Now I have observed a fast and my own fat and blood have been diminished. May it be thy will that my diminished fat and blood be accounted as though I had offered them up before thee on the altar, and do thou show me favor." (Berakhot 17a).(2)
This idea is echoed quite often in the prayer books for the High Holy Days.(3)
Jesus fasted for forty days and forty nights in the desert (Matthew 4:2). Moses and Elijah also fasted for a period of forty days although that may have been a different kind of fast.
Jesus also made it clear that fasting was to be a private thing, between you and the Father. He was opposed to public fasting for the benefit of pride.
TSUM was the Mosaic expression for fasting.
Some traditions hold that on the day before Yom Kippur and on the Sabbath it is forbidden to fast.
Sometimes people fast from other things besides food.
There seem to be four fast days that commemorate the destruction of either the first or the second temple (Rosh Hashanah 18b). All four are man made fast days that began after 586 B.C. when the Babylonians destroyed Solomon's temple. The four fast are:
The fast of the tenth of Tevet.
The fast of the seventeenth of Tammuz.
The fast of Gedaliah.
The fast of Tisha B'av.
One area of Persian law declared a person could not come into the king's presence without being summoned. If they did, it was possible to be put to death as a punishment. Esther fasted for three days to prepare herself, and then went to the king. He welcomed her and the Lord provided.
Find out more about Fast Days observed in the Jewish Religion:
1). The Feast of Israel by Bruce Scott of Friends of Israel ministries.
2). The Fall Feasts of Israel by Mitch and Zhava Galser.
3). ArtScroll Tanach Series on Daniel, p.243.