gut-health · 1 min read
How much fiber in a banana? About 3.1 g in a medium one
A medium banana contains roughly 3.1 g of fiber, about 12% of the daily target for women. Greener bananas carry more resistant starch, which behaves like fiber and falls as the fruit ripens.
Written by Lifebar Desk · Checked against the sources listed below
Published 20 Sept 2026
Key takeaways
- A medium banana carries about 3.1 g of fiber, a large one closer to 4 g.
- Underripe bananas contain resistant starch, which is fermented like fiber and largely disappears as they ripen.
- Bananas sit mid-table among fruits, below berries and pears.
- They are a better potassium source than fiber source, at roughly 420 mg per medium fruit.
A medium banana contains roughly 3.1 g of fiber. That places it squarely in the middle of the fruit table, well below berries and pears, and slightly below an apple.
The numbers
| Size | Weight | Fiber |
|---|---|---|
| Small | ~101 g | ~2.6 g |
| Medium | ~118 g | ~3.1 g |
| Large | ~136 g | ~3.5 g |
| Extra large | ~152 g | ~4 g |
The resistant starch complication
Ripeness changes what a banana does in your gut even though the labelled fiber barely moves. A green banana is high in resistant starch, a carbohydrate that escapes digestion in the small intestine and gets fermented by bacteria in the colon, producing short-chain fatty acids much as fiber does. As the fruit ripens that starch converts to simple sugars, which is why a spotty banana tastes sweeter and feeds your microbiome less.
What a banana is actually good for
Potassium, mostly. A medium banana supplies roughly 420 mg, around 9% of the adequate intake for adults, alongside vitamin B6 and a quick, well-tolerated dose of carbohydrate. It earns its reputation as portable fuel more than as a fiber food.
Against the daily target
At 3.1 g, a banana covers about 12% of the 25 g target for women and 8% of the 38 g target for men. Reaching the target on bananas alone would take eight to twelve of them, which is a useful sense of scale for how much fruit fiber actually contributes.
One caveat
Published fiber values for bananas vary a little between databases and cultivars, and resistant starch is measured inconsistently. Treat 3 g as the working figure for a medium banana rather than a precise constant.
Frequently asked
How much fiber is in one banana?
About 3.1 g for a medium banana of roughly 118 g. Small bananas land near 2.6 g and large ones near 4 g.
Are green bananas higher in fiber?
They contain more resistant starch, which resists digestion in the small intestine and is fermented in the colon much as fiber is. Standard nutrition labels do not count it as fiber, so the labelled figure understates the effect of an underripe banana.
Do bananas help or worsen constipation?
Ripe bananas are mildly helpful for most people. Underripe ones are higher in resistant starch and tannins and are occasionally reported to do the opposite. Neither effect is strong, and a banana is not a treatment for constipation.
Sources
Educational content, talk to your clinician before changing treatment.
