I was cross-referencing verses for a teaching inside Project Kingdom Gladiator. I hit a footnote I’d skipped past for years: “some manuscripts add and fasting.” That sent me down a real rabbit hole into what the Bible actually says about fasting. Scripture says less than I assumed. The tradition around it had quietly filled in the gaps.
What does the Bible say about fasting? It’s voluntary in every case except one: the Day of Atonement (Leviticus 16:29). Scripture never commands fasting for New Testament believers, and it never sets a required length, method, or formula. Jesus assumed His followers would fast (“when you fast,” not “if you fast,” Matthew 6:16-18), but He cared more about why you fasted than how long. A few popular fasting proof-texts, including Matthew 17:21 and part of Acts 10:30, aren’t even in the earliest manuscripts we have.
The Short Answer: Voluntary, With One Exception
Search “what does the Bible say about fasting” and you’ll find a hundred pages telling you it’s commanded. Go check the text yourself. That’s not what you find.
God commanded only one fast in scripture: the Day of Atonement. He told Israel to “afflict your souls” (Leviticus 16:29, 23:27). Jewish tradition and later scripture itself (Isaiah 58:3, 58:5) both interpret that Hebrew phrase as fasting. That’s it. One command, one day a year, under the Old Covenant.
People chose every other fast in the Bible, from Moses to Daniel to Jesus to the early church in Acts. Nobody ordered it. Nobody broke a law by skipping it.
What the Actual Words Say
Jesus never told His disciples they had to fast. He also never suggested they wouldn’t.
Matthew 6:16-18 opens with “when you fast,” the same construction He used for “when you pray” a few verses earlier. He’s not issuing a command. He’s describing a normal rhythm of a devoted life, the same way you’d say “when you brush your teeth” without implying a legal requirement. Bible.org’s survey of the passage reads it the same way: assumed practice, not mandated obligation.
That’s the grammar of the only extended teaching Jesus gave on fasting. People read a lot into the text beyond it: that it’s required, that it has to hit a certain number of days, that God owes you something for doing it. The text never states any of that.
The Fasting Verses That Didn’t Make the Cut
Here’s something most fasting content skips. It matters if you actually want to know what scripture says, not just what got added to it later.
Three of the most quoted fasting verses have a textual problem. In Mark 9:29, Jesus says a certain kind of demon “cannot come out by anything but prayer.” Later manuscripts added the words “and fasting.” The two oldest and most reliable copies we have, Codex Sinaiticus and Codex Vaticanus, just say “prayer.” Matthew 17:21, the parallel verse, doesn’t appear in those same early manuscripts at all. Scribes likely copied it in from the longer version of Mark. Acts 10:30 has the same issue: several of the earliest Greek manuscripts and early translations leave out the word “fasting.”
This isn’t a fringe theory. It’s why modern translations like the ESV and NIV drop these words or flag them in a footnote. They’re working from the same manuscript evidence textual scholars have studied for over a century. Here’s the likely explanation: fasting became a bigger deal in church practice over the following centuries, and some scribes added it to verses that originally only mentioned prayer.
I’m not bringing this up to argue fasting doesn’t matter. I’m bringing it up because you asked what scripture actually says. The honest answer: people attached some fasting traditions to the text over time that were never in the original.
What Scripture Never Says
People assume the Bible specifies fasting length, method, or a formula for results. It doesn’t, anywhere.
There’s no verse telling you a fast has to be 24 hours, 3 days, or 40 days to count. Daniel fasted 21 days and only from certain foods (Daniel 10:2-3). Esther called for 3 days, no food or water (Esther 4:16). Jesus went 40 days in the wilderness (Matthew 4:1-2). Scripture doesn’t prescribe any of those lengths for anyone else. They’re just what those specific people did in those specific situations.
There’s also no verse where fasting works like a lever you pull to guarantee an outcome from God. Isaiah 58 makes this point bluntly. God’s people fasted and complained that God wasn’t responding. God told them their fasting was hollow, because they were still mistreating workers and ignoring the poor the whole time (Isaiah 58:3-7). Fasting didn’t obligate God to anything. It never does.
Was Fasting Only an Old Testament Requirement?
No. This is where people misread the text in the other direction. They assume that because God commanded only one Old Testament fast, fasting itself was just a Jewish law that ended at the cross.
That’s not what the record shows. The early church in Acts kept fasting voluntarily, well after Jesus rose. The church at Antioch was fasting when the Holy Spirit set apart Paul and Barnabas for their mission (Acts 13:2-3). Paul and Barnabas fasted again every time they appointed elders in a new church (Acts 14:23). Nobody told them to. They just kept doing it. Jesus had assumed they would, and it kept working as a way to focus on God during weighty decisions.
Fasting Predates the Bible, and That’s Not a Problem
Here’s a fair question, one a skeptic would raise. Fasting shows up in Sumerian, Egyptian, and Greek religious practice long before Israel existed. Doesn’t that mean the Bible just borrowed a generic ancient ritual instead of receiving something from God?
The practice, sure. Going without food to focus on something bigger than yourself is a nearly universal human instinct. Scripture never claims Israel invented it. What’s different isn’t the mechanics of skipping food. It’s who you’re doing it for, and why. Scripture says you’re not trying to manipulate capricious gods into a favor. You’re seeking the attention of one specific God, who already knows what you need before you ask (Matthew 6:8). Same practice, a completely different posture behind it.
How This Actually Changes the Way I Fast
Going back to the actual text, instead of the version I’d absorbed secondhand, changed how I fast now.
I stopped treating my weekly fast as a box to check. Worse, I stopped using it to force God’s hand: fast hard enough and He has to answer. Nothing in scripture supports that. Scripture supports fasting as a specific conversation with a specific purpose. Hold it loosely. Want more of God, not a result from Him. [NEED: photo of the concordance/study notes from when I first dug into this]
Want the full theology of fasting? I laid out the seven biblical reasons people fasted and the four major individual fasts here. Ready for the practical side, how long to fast, what to drink, how to break it safely? That’s covered step-by-step here. Want the research on fasting for weight loss, plus who shouldn’t fast at all? The full pillar post covers it.
I’m a personal trainer, certified since 2011. I built Project Kingdom Gladiator after going back to scripture myself, instead of trusting what I’d always assumed it said, about fasting and a lot else. You can read more about that at tylerinloes.com/about.
Next time someone tells you what the Bible says about fasting, go check it yourself. That’s the whole point of this post.
