Explainer 1 min read

Soluble vs. Insoluble Fibre: What's the Difference?

Soluble fibre dissolves in water and feeds your gut bacteria. Insoluble fibre doesn't dissolve. It adds bulk and helps things move. You need both.

Reviewed by our gut-microbiome scientists Built on 10+ years of MIT research

The short answer

The split isn't about which is better. It's about what each one does. Most whole foods contain a mix of both.

Soluble fibre dissolves into a gel and is the type most easily fermented by gut bacteria.
Insoluble fibre stays intact and adds bulk, helping food move through your gut.
Most fibre-rich foods contain both, though the ratio varies.

Two different jobs, not a competition

Soluble fibre dissolves in water, forming a gel your gut bacteria can ferment. Insoluble fibre doesn't dissolve. It stays intact and adds bulk, helping food move through your gut. Most whole foods contain some of both; the ratio is what varies.

Why the fermentable, soluble kind gets most of the research attention

Soluble fibre is the type most easily broken down by gut bacteria, which is why most prebiotic fibre research focuses there. Insoluble fibre still matters for regularity, but if your goal is feeding your gut microbiome specifically, soluble, fermentable fibre is doing most of that work.

Soluble fibre

Dissolves and ferments

Forms a gel in water. Slowly fermented by gut bacteria, producing the compounds that support gut lining health.

Insoluble fibre

Adds bulk

Passes through largely intact, adding bulk to stool and helping food move through the digestive tract.

Getting enough total fibre matters. So does getting a mix of both types, in enough variety within each.

You need the mix, not just the max

Getting enough total fibre matters, but so does getting the right mix of soluble and insoluble types — and enough variety within each. Our blend combines multiple fibres in the ratios our team arrived at through a decade of research at MIT. One spoonful, stirred into whatever you're already having.

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