Chemically modified resistant starch · RS4

Fiber, reimagined from the starch up.

Fiber Labs Health makes RS4 — a resistant starch and prebiotic fiber that travels through your small intestine intact and is fermented by the bacteria in your gut.

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Prebiotic dietary fiber Resists digestion Fermented in the colon

Type 4Resistant starch

Fiber Labs Health RS4 resistant starch tub

SCFAsFermentation by-products

The basics

So, what exactly is RS4?

Resistant starch is starch that resists digestion in the small intestine. There are several types — RS4 is the chemically modified kind, engineered in the lab to stay intact until it reaches your gut microbiome.

Made, not foraged

Unlike RS1–RS3 found in foods, RS4 is produced by chemically modifying starch — for example through cross-linking, esterification or etherification.

Built to resist

Those modifications make the starch highly resistant to the digestive enzymes in your small intestine, so it passes through largely unbroken.

Reaches the colon

Because it isn’t absorbed up top, RS4 arrives intact in the large intestine — the home of trillions of gut bacteria.

Food for microbes

There, gut bacteria ferment it — which is what makes RS4 a prebiotic: a fiber that feeds the microbiome rather than you.

The journey

From spoon to microbiome

A simplified look at the path RS4 takes through the body — and why fermentation in the colon is the whole point.

You eat it

Stir RS4 into water, coffee, smoothies or food. It’s a fine, neutral starch — no graininess, no strong taste.

It resists

Through the stomach and small intestine, the chemical modifications keep digestive enzymes from breaking it down.

It ferments

In the colon, resident bacteria ferment the starch — a natural process that selectively nourishes parts of the microbiome.

SCFAs form

Fermentation produces short-chain fatty acids such as butyrate, acetate and propionate — the molecules researchers study most.

What researchers have studied

The science of resistant starch

RS4 and resistant starch are an active area of microbiome research. Here are a few peer-reviewed studies worth reading for yourself.

Human study · PLOS ONE 2010

RS2 vs RS4 shift different bacteria

In a controlled human trial, RS4 was associated with increases in Bifidobacterium adolescentis and Parabacteroides distasonis in the fecal microbiota — distinct from the shifts seen with RS2.

Read the study In vitro · Frontiers 2021

Butyrate output depends on the source

Laboratory fermentation showed that how much butyrate gut microbes produce from resistant starch depends on both the starch source and an individual’s microbiome composition.

Read the study Human study · mBio 2017

Mapping the microbiome’s response

A multi-omics study tracked how dietary resistant starch changes the human gut microbiome, metaproteome and metabolome — documenting measurable shifts in community activity.

Read the study

These summaries describe published research on resistant starch for educational purposes. They are observations from independent studies — not statements about this specific product, and not a promise of any result for you.

Fiber Labs Health · RS4

Buy it now and start your health journey.
We wish your microbiome the best.

One clean, chemically modified resistant starch. Unflavored, mixes into anything, and made for people who like to understand what they put in their body.

$39 / 30-serving tub Founding batch

Unflavored & mixable 30 servings Prebiotic fiber

Fiber, re​imagined from the starch up.