Soluble vs Insoluble Fibre: What the Difference Actually Means
By Kevin · Founder, Ryedical · Updated 17 July 2026
The difference in one line: soluble fibre dissolves in water and forms a gel that slows digestion, while insoluble fibre doesn't dissolve and instead adds bulk that keeps everything moving. They do different jobs, most foods contain a mix of both, and a healthy intake includes both types.
What soluble fibre does
When soluble fibre meets water it thickens into a gel. That gel slows how quickly food leaves the stomach, which supports a feeling of fullness between meals†, and it slows how quickly nutrients are absorbed, which supports a steadier energy release†. Soluble fibre is also the type most fermented by gut bacteria, which is where it overlaps with prebiotics.
Where you find it: oats and oat bran (beta-glucan), psyllium husk, legumes, barley, and the flesh of fruit like apples and citrus.
What insoluble fibre does
Insoluble fibre passes through largely intact. It adds bulk and holds water, which supports regular, predictable gut function†. It's the structural fibre: the skins, husks, and outer layers of plants.
Where you find it: wheat bran, wholegrains, the skins of fruit and vegetables, nuts, and seeds.
Why you need both
Because the jobs don't substitute for each other. All gel and no bulk, or all bulk and no gel, each misses half the picture. Dietary guidelines don't set separate targets for the two types; the practical advice is to eat a variety of plant foods so both arrive together.
Foods that give you both at once
Most plant foods carry a mix, but a few are notably balanced. Rye bran is one of them: unlike wheat bran (strongly insoluble) or oat bran (strongly soluble), rye bran carries meaningful amounts of both fibre types naturally in the same grain layer. That's one reason a single tablespoon works as a general-purpose fibre topper rather than a specialist one.
Where Ryedical fits
Ryedical is 100% cold-processed rye bran: about 5g of fibre per tablespoon, with both soluble and insoluble fractions naturally present†. Note that rye bran contains gluten and is not suitable for people with coeliac disease or non-coeliac gluten sensitivity.
Related reading
- How much fibre do you actually need each day?
- Rye bran vs wheat bran vs oat bran: what's the difference?
- What's in each tablespoon
†As part of a balanced diet.
This article is general information and does not provide medical advice. Speak with your healthcare professional about your specific dietary needs.