Soluble vs Insoluble Fibre: What Is the Difference?
TL;DR: Soluble vs insoluble fibre comes down to water. Soluble fibre dissolves or swells in water to form a gel, like oats and psyllium. Insoluble fibre does not dissolve and adds bulk, like wheat bran and vegetable skins. Most foods have both. Most Australians do not eat enough fibre of either kind. Dietary fibre contributes to regular laxation.
Fibre is not one thing.
Drop some in a glass of water and you will see.
Soluble fibre
Soluble fibre takes up water and forms a gel. You find it in oats, barley, legumes, apples, citrus, psyllium and slippery elm. Some soluble fibres, like inulin, are also prebiotics: gut bacteria can ferment them.
Insoluble fibre
Insoluble fibre does not dissolve. It passes through largely unchanged and adds bulk. Wheat bran, wholegrains, nuts, seeds and the skins of fruit and vegetables are good sources.
Side by side
| Soluble | Insoluble | |
|---|---|---|
| In water | Swells or dissolves, forms a gel | Stays as it is |
| Food sources | Oats, legumes, apples, psyllium | Wheat bran, wholegrains, skins |
| Texture | Thick, smooth | Rough, bulky |
Your move: add one food from each column to your day.
How much do you need?
The NHMRC sets adequate intakes of 30 g a day for men and 25 g for women, with no split between types. Details in how much fibre per day.
A powder with both
Gut Health Powder is a soluble and insoluble fibre powder: psyllium husk, slippery elm bark, yucca root, organic inulin and rice bran, with 4.1 g of dietary fibre per 8 g serve.
Frequently asked questions
Is one type better?
No. Most fibre-rich foods contain both, and a varied diet covers both.
Is inulin soluble?
Yes. See inulin vs psyllium husk.
Why drink water with fibre?
Soluble fibre takes up water, so drinking enough helps it go down smoothly.
References
National Health and Medical Research Council (2006, updated). Nutrient Reference Values for Australia and New Zealand: Dietary Fibre.
Propel Health Australia. Gut Health Powder 240 g label.
About the author
Grant Jenkins is co-founder of Propel Health Australia, an Australian, family-owned company based in Brisbane, Queensland, and an ESSA Accredited Exercise Physiologist. Every Propel Health figure quoted here is the figure on the pack.
Disclaimer
This article is general information, not medical advice. Gut Health Powder is a food, taken as part of a balanced diet. Fibre can affect how some medicines are taken up, so leave about two hours between them and ask your pharmacist. Speak to your healthcare provider before starting anything new, especially if you are pregnant, breastfeeding or under medical supervision.
