Jesus' statements concerning fasting are simple and straightforward. His disciples will fast (Luke 5:33-35 Luke 5:33-35  And they said to him, Why do the disciples of John fast often, and make prayers, and likewise the disciples of the Pharisees; but your eat and drink?
 And he said to them, Can you make the children of the bridal chamber fast, while the bridegroom is with them?
 But the days will come, when the bridegroom shall be taken away from them, and then shall they fast in those days.
American King James Version×), but He did not specify how long or how often. As Paul amplified in Romans, fasting is an individual concern between us and Jesus Christ, who is our judge.
Fasting of any length should be approached as an all important tool to draw closer to God.
The Bible has only one command regarding fasting: God's people are commanded to fast on the Day of Atonement from sundown to sundown (Leviticus 23:27-32 Leviticus 23:27-32  Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation to you; and you shall afflict your souls, and offer an offering made by fire to the LORD.
 And you shall do no work in that same day: for it is a day of atonement, to make an atonement for you before the LORD your God.
 For whatever soul it be that shall not be afflicted in that same day, he shall be cut off from among his people.
 And whatever soul it be that does any work in that same day, the same soul will I destroy from among his people.
 You shall do no manner of work: it shall be a statute for ever throughout your generations in all your dwellings.
 It shall be to you a sabbath of rest, and you shall afflict your souls: in the ninth day of the month at even, from even to even, shall you celebrate your sabbath.
American King James Version×). This meant they were to fast—to go without food and water—for a period of 24 hours.
Interestingly, this fast day is listed among God's spiritual Feast days. To learn about the meaning of the Day of Atonement and its accompanying fasting, please request our free booklet God's Holy Day Plan: The Promise of Hope for All Mankind.
Choosing a length
How long we might safely fast depends on our individual health.
In a sense, everyone fasts. When we are in bed asleep, we go without any food or drink. That is fasting. That is why the first meal of the day is called breakfast. However, when people speak of fasting, they usually mean a longer period of time of deliberately choosing not to eat and drink. It can be for a whole day, part of a day or more than a day.
If you've never fasted before, a commitment of a day may be easier to accomplish and will familiarize you with the process. Use that first experience to learn what your body's particular reactions are.
Another option is a partial fast such as that mentioned in Daniel 10:3 Daniel 10:3I ate no pleasant bread, neither came flesh nor wine in my mouth, neither did I anoint myself at all, till three whole weeks were fulfilled.
American King James Version×. Here one takes in only as much food and/or water as necessary to be safe and spends extra time in prayer, Bible study and meditation. This, too, can be very profitable spiritually.
A healthy person who is not perspiring much can go without food and water for about three days before the body begins to be stressed. And a healthy person can go without food for several days if he is drinking water. Thus, the amazingly long 40-day fasts by Moses, Elijah and Jesus Christ (Deuteronomy 9:9 Deuteronomy 9:9When I was gone up into the mount to receive the tables of stone, even the tables of the covenant which the LORD made with you, then I stayed in the mount forty days and forty nights, I neither did eat bread nor drink water:
American King James Version×; 1 Kings 19:8 1 Kings 19:8And he arose, and did eat and drink, and went in the strength of that meat forty days and forty nights to Horeb the mount of God.
American King James Version×; Luke 4:2 Luke 4:2Being forty days tempted of the devil. And in those days he did eat nothing: and when they were ended, he afterward hungry.
American King James Version×) were possible only by God's supernatural intervention.
The length of time that someone fasts should always be the length that is right for them at the time. Remain flexible. Of course you'll have a goal in mind when you begin, but don't be too inflexible to end the fast should your body signal. Severe pain and discomfort may mean you have attempted too much, too soon.
Those interested in longer-term fasts are advised to break their fast if and when “true hunger” appears. Be careful not to fast too frequently; allow your body sufficient time to rebuild nutritional reserves. We encourage those with health problems to consult a qualified medical practitioner before fasting.
Fasting is highly personal
While a 24-hour period is the most common length for fasting, any amount of time can be chosen, depending on your particular situation.
Remember, fasting is for one's spiritual health, which involves abstaining from food and drink while spending a lot of extra time in prayer and Bible study (Exodus 34:28 Exodus 34:28And he was there with the LORD forty days and forty nights; he did neither eat bread, nor drink water. And he wrote on the tables the words of the covenant, the ten commandments.
American King James Version×; Ezra 10:6 Ezra 10:6Then Ezra rose up from before the house of God, and went into the chamber of Johanan the son of Eliashib: and when he came thither, he did eat no bread, nor drink water: for he mourned because of the transgression of them that had been carried away.
American King James Version×; Esther 4:16 Esther 4:16Go, gather together all the Jews that are present in Shushan, and fast you for me, and neither eat nor drink three days, night or day: I also and my maidens will fast likewise; and so will I go in to the king, which is not according to the law: and if I perish, I perish.
American King James Version×; Acts 9:9 Acts 9:9And he was three days without sight, and neither did eat nor drink.
American King James Version×).
When deciding how long to fast, consider when the time is right and you can be truly devoted to the process, instead of trying to squeeze them into a too-busy life. Fasting of any length should be approached as an all important tool to draw closer to God.