What is fasting, and should Christians do it?

What Is Fasting?

Fasting, in the biblical sense, is the voluntary abstention from food — and sometimes drink — for a set period, for spiritual purposes. It is not a diet. It is not a hunger strike. It is not a way of twisting God's arm into answering prayer. It is a deliberate act of self-denial in which physical hunger is redirected toward spiritual longing — a bodily expression of dependence on God that goes beyond what words alone can say.

The Hebrew word most commonly used is tsum (צוּם), meaning to abstain or withhold. The Greek word is nēsteia (νηστεία), from nē- (not) and esthiō (to eat) — literally "not eating." Both words appear throughout their respective Testaments in contexts ranging from mourning and repentance to urgent prayer and spiritual warfare.

Fasting in the Old Testament

Fasting appears throughout the Old Testament as a natural accompaniment to serious prayer, grief, repentance, and seeking God's direction.

Moses fasted for forty days on Mount Sinai when receiving the Law: "I stayed on the mountain forty days and forty nights; I ate no bread and drank no water" (Deuteronomy 9:9). He did it again after the golden calf (v. 18). The forty-day fast at a moment of national crisis and covenant renewal becomes a pattern that echoes through Scripture.

David fasted when his infant son was sick: "David pleaded with God for the child. He fasted and spent the nights lying in sackcloth on the ground" (2 Samuel 12:16). When the child died, he stopped fasting — explaining to his servants: "While the child was still alive, I fasted and wept. I thought, 'Who knows? The LORD may be gracious to me and let the child live.' But now that he is dead, why should I go on fasting?" (vv. 22–23). David's fasting was an earnest appeal to God, not a mechanical performance.

Esther calls the Jewish people to a three-day fast before she approaches the king uninvited — a potentially fatal act: "Do not eat or drink for three days, night or day. I and my attendants will fast as you do" (Esther 4:16). The fast accompanies a moment of mortal danger and complete dependence on God.

Ezra fasts at the river Ahava before leading the exiles back to Jerusalem: "There, by the Ahava Canal, I proclaimed a fast, so that we might humble ourselves before our God and ask him for a safe journey for us and our children, with all our possessions" (Ezra 8:21). He explicitly connects fasting with humility before God.

Nehemiah responds to the news of Jerusalem's broken walls with fasting and prayer: "When I heard these things, I sat down and wept. For some days I mourned and fasted and prayed before the God of heaven" (Nehemiah 1:4).

The prophet Joel calls the whole nation to a fast in the face of judgment: "Even now, declares the LORD, return to me with all your heart, with fasting and weeping and mourning" (Joel 2:12). And Isaiah 58 gives perhaps the Bible's most important corrective on fasting — God rejects the fasting of people who oppress their workers and ignore the poor, and calls instead for a fast expressed in justice and care for the vulnerable (Isaiah 58:3–7).

Jesus and Fasting

Jesus's teaching on fasting in the Sermon on the Mount is revealing both for what he says and how he says it. In Matthew 6:16–18, he does not say "if you fast" — he says "when you fast": "When you fast, do not look sombre as the hypocrites do, for they disfigure their faces to show others they are fasting... But when you fast, put oil on your head and wash your face, so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen."

The assumption is that his followers will fast. The instruction is about how to do it rightly: privately, without display, directed toward God rather than human audience. Fasting done for public admiration has already received its reward — the admiration. Fasting done before God alone is the kind that God rewards.

Jesus himself fasted for forty days in the wilderness before his public ministry began (Matthew 4:2). He faced the full weight of hunger — "he was hungry" (v. 2) — and was then tempted by Satan to turn stones to bread. His response — "Man shall not live on bread alone, but on every word that comes from the mouth of God" (v. 4, quoting Deuteronomy 8:3) — is precisely the truth that fasting enacts: that there is a deeper hunger than physical hunger, and a more essential sustenance than food.

When asked why his disciples did not fast while the Pharisees' disciples did, Jesus replied: "How can the guests of the bridegroom fast while he is with them? The time will come when the bridegroom will be taken from them; then they will fast" (Matthew 9:15). Jesus is the bridegroom — while he is physically present, the disciples are at a wedding feast. After his ascension, fasting resumes as the normal practice of those who long for the bridegroom's return.

Fasting in the Early Church

The early church fasted regularly and specifically. Acts 13:2–3 records that the church at Antioch was "worshipping the Lord and fasting" when the Holy Spirit directed them to set apart Paul and Barnabas for missionary work — and they fasted again before sending them off. Acts 14:23 records Paul and Barnabas appointing elders in every church "with prayer and fasting." Fasting accompanied major decisions, transitions, and the commissioning of leaders.

The Didache — one of the earliest Christian documents outside the New Testament, dated to around AD 100 — instructs believers to fast on Wednesdays and Fridays rather than the Jewish days of Monday and Thursday. This shows that by the end of the first century, fasting had become a structured part of Christian practice, with the church deliberately distinguishing its fast days from those of surrounding Jewish practice.

Why Fast? What Does It Do?

John Piper, in A Hunger for God: Desiring God Through Fasting and Prayer (Crossway, 1997) — the most widely read modern treatment of the subject — argues that the essence of fasting is this: "Fasting is the body's way of saying, 'I am so gripped by this spiritual reality that I am not going to stop to eat.'" It is hunger for God made physical. When the body says "I need food" and the spirit says "I need God more," fasting is what happens when the spirit wins that argument.

Scripture suggests several connected purposes:

Humbling oneself before God. Psalm 35:13 — "I humbled myself with fasting." Ezra 8:21 explicitly connects fasting with humbling oneself before God. Fasting is a bodily acknowledgment of dependence — a way of saying with the whole person, not just the mouth, "I am not self-sufficient."

Intensifying prayer. Fasting and prayer are consistently paired throughout Scripture. The combination appears to intensify earnestness — when you skip meals to pray, the growling stomach becomes a reminder to return to prayer. It gives prayer a physical weight and urgency that words alone do not carry.

Seeking God's guidance. The church in Antioch was fasting when the Spirit spoke (Acts 13:2). Fasting creates attentiveness — a quieting of normal appetites that seems to make it easier to hear what God is saying.

Repentance and mourning. In the Old Testament especially, fasting accompanies grief over sin — both personal and corporate. Joel 2:12 calls for fasting as part of returning to God with the whole heart. The fast is the body participating in what the heart is expressing.

Spiritual warfare. In Matthew 17:21 (in some manuscripts), Jesus indicates that certain demonic strongholds are only broken "by prayer and fasting." The implication is that there is spiritual power released in fasting that is not available through prayer alone.

Should Christians Fast Today?

Given Jesus's assumption in Matthew 6 ("when you fast"), the early church's regular practice, and the consistent witness of Christian history — including figures like Augustine, John Calvin, John Wesley, and countless others who maintained regular fasting — the answer from Scripture is yes.

Fasting is not commanded as a law in the New Testament the way certain Old Testament fasts were (e.g., the Day of Atonement fast in Leviticus 23:27). It is practised voluntarily, freely, in response to spiritual need. But Jesus's "when" — not "if" — makes it clear that the expectation is that his followers will fast.

Practically, there is no single prescribed form. A fast might mean skipping one meal and using that time to pray. It might mean a day of water-only. It might mean abstaining from a particular food or habit (some Christians fast from social media or entertainment in the spirit of the discipline). Medical conditions should always be taken into account — diabetics, those with eating disorders, pregnant women, and others have real physical reasons to approach food restriction carefully. Fasting is meant to direct attention to God, not to harm the body.

The goal is never the fast itself. Isaiah 58 stands as the permanent corrective: God is not impressed by religious fasting that coexists with injustice and indifference to the poor. The fast he desires is one that breaks chains, feeds the hungry, and shelters the homeless — the outward practice flowing from an inward reality of genuine dependence on and love for God.

"When you fast, do not look sombre as the hypocrites do... But when you fast, put oil on your head and wash your face, so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you." — Matthew 6:16–18 (NIV)

For further reading: John Piper, A Hunger for God (Crossway, 1997) — the definitive modern treatment, combining theology, history, and practical guidance. Richard Foster, Celebration of Discipline (HarperOne, 1978) — Chapter 4 covers fasting as one of the classical spiritual disciplines; widely regarded as the best introduction to the disciplines as a whole. GotQuestions.org's article "What does the Bible say about fasting?" is a thorough biblical survey.