Fasting and prayer: what the Bible says and how churches fast

Fasting runs through the whole Bible — Moses, David, Esther, Daniel, Anna, Jesus, the church at Antioch — and yet the texts give remarkably few instructions about how to do it. What they do give is a set of warnings about why, and those are the parts most often skipped.

What Jesus actually said about fasting

The instruction in the Sermon on the Mount is not about method. It is about concealment.

“Moreover when you fast, don’t be like the hypocrites, with sad faces. For they disfigure their faces that they may be seen by men to be fasting. Most certainly I tell you, they have received their reward. But you, when you fast, anoint your head and wash your face, so that you are not seen by men to be fasting, but by your Father who is in secret; and your Father, who sees in secret, will reward you. (Matthew 6:16-18, read the chapter)

Note the assumption buried in the grammar: "when you fast", not "if". Fasting is taken for granted. What is forbidden is the visible version — the announced fast, the fast that functions as a credential.

Elsewhere Jesus is asked why his disciples do not fast when John's disciples and the Pharisees do. His answer is a wedding image: "Can the friends of the bridegroom mourn as long as the bridegroom is with them? But the days will come when the bridegroom will be taken away from them, and then they will fast." (Matthew 9:15) Fasting is tied to a season, not to a permanent rule.

The fast Isaiah describes

The sharpest passage on fasting in the Old Testament is a complaint about people who fasted correctly and lived badly.

“Isn’t this the fast that I have chosen: to release the bonds of wickedness, to undo the straps of the yoke, to let the oppressed go free, and that you break every yoke? Isn’t it to distribute your bread to the hungry, and that you bring the poor who are cast out to your house? (Isaiah 58:6-7, read the chapter)

The prophet Joel adds the internal version: "Tear your heart and not your garments" (Joel 2:13) — a jab at a mourning ritual performed on clothing rather than in a life.

Fasting attached to a decision

Two passages in Acts connect fasting to sending people out and appointing leaders:

As they served the Lord and fasted, the Holy Spirit said, “Separate Barnabas and Saul for me, for the work to which I have called them.” Then, when they had fasted and prayed and laid their hands on them, they sent them away. (Acts 13:2-3)

And later: "When they had appointed elders for them in every assembly, and had prayed with fasting, they commended them to the Lord on whom they had believed." (Acts 14:23) In both cases the fast surrounds a decision the community was making together. That pattern — fasting before something consequential — is the one most Christian traditions have kept.

How each tradition fasts today

Practice varies a great deal, and none of these is a summary of the others.

Catholic obligations are set out in the Code of Canon Law, canons 1249 to 1253, which fix Ash Wednesday and Good Friday as days of both fasting and abstinence and hand the details to national bishops' conferences. Orthodox fasting is stricter in kind and far more frequent in the calendar, and is usually described as something worked out with a confessor rather than applied uniformly. Protestant practice divides mostly between traditions that kept a liturgical calendar and traditions that did not.

What actually happens during a fast

The devotional literature tends to skip the physical part, which is a mistake, because the physical part is most of the first experience.

A one-day food fast for a healthy adult usually goes: mild hunger by late morning, a low-grade headache in the afternoon (often caffeine withdrawal rather than hunger), irritability around the usual dinner time, and then the odd discovery that the evening is unusually long. Concentration dips. Most people find they are worse company, not more spiritual, and that is worth knowing in advance rather than treating as a failure.

The prayer part is not automatic. If nothing is planned, a fast day becomes a day of being hungry and slightly cross. What makes the difference is deciding beforehand what occupies the gap — the twenty minutes that would have been lunch, the money not spent, the hour freed by not watching anything. Traditions that legislate fasting almost always pair it with something else: prayer and almsgiving in the Catholic Lenten triad, longer services and confession in Orthodox practice.

Breaking a fast matters too, in an unglamorous way. Ending a day-long fast with a very large meal is uncomfortable and, after longer fasts, genuinely risky; the traditions that fast for weeks all reintroduce food gradually.

What fasting does not buy

This is the point at which a lot of writing goes wrong. Nothing in these texts presents fasting as a lever.

• It does not oblige God to act. Isaiah 58 is precisely a rebuke of people who assumed it did.
• It does not measure spiritual seriousness. Luke's Pharisee announces that he fasts twice a week and is not the character the parable commends.
• It is not required of Christians by any New Testament command. Jesus assumes it and does not schedule it; Paul never instructs a church to fast.

Who should not fast

Fasting is a physical act with physical consequences, and there are people for whom it is simply not safe. Anyone who is pregnant or breastfeeding, has diabetes or another condition affecting blood sugar, has a history of an eating disorder, takes medication that must be swallowed with food, or is recovering from illness or surgery should speak to a doctor before altering how they eat. Children and older adults are treated as exempt in the traditions that legislate fasting at all, and that exemption exists for good reason. This article is not medical advice and does not replace the guidance of your own doctor.

Where food is not appropriate, most traditions accept a substitution — silence, screens, spending, alcohol — and the Catholic canons explicitly allow bishops' conferences to substitute other forms of penance.

A modest way to start

If you want to try it, one day is enough. Pick a day, pick one meal or one habit, decide in advance what you will do with the time or money released, tell nobody, and attach a specific prayer to it — often a decision you are weighing or a person you are carrying. The prayer for making a decision and the prayer for strength fit that use, and the article on praying before a hard decision covers the discernment side. If you want the wider picture of how different churches pray, see how each Christian tradition prays.