The Short Answer
Psyllium is a husk from the seed of Plantago ovata, used largely unprocessed. Resistant dextrin is a manufactured ingredient, made by heating and enzymatically treating starch until most of it resists digestion. Psyllium thickens and gels in water; resistant dextrin dissolves clear. Both count as dietary fibre in Australia, but they reached that status by different regulatory routes.
Where Each Comes From
Psyllium husk is the seed coat of the psyllium plant, separated out and milled, with minimal further processing. Resistant dextrin is produced industrially: starch (commonly from maize, wheat or potato depending on the manufacturer) is heated under acidic conditions and treated with enzymes, a process that rearranges some of the glucose bonds into forms human digestive enzymes can't break down.
Solubility and Texture: Gel vs Clear Dissolve
This is the most noticeable practical difference. Psyllium's husk is largely arabinoxylan, a highly branched soluble fibre that absorbs many times its own weight in water and forms a weak, elastic gel rather than dissolving. Research on psyllium mucilage describes this gel as shear-thinning: thick at rest, thinner when stirred, and increasingly structured as extraction and processing conditions change its molecular weight. Resistant dextrin has a far more compact, branched structure that disperses into water with little thickening at typical use levels, dissolving close to clear.
Fermentability
Both are at least partly fermented by gut bacteria in the large intestine, which is part of why both qualify as dietary fibre under the Food Standards Code. The specific rate and extent of fermentation differs by ingredient, processing and individual gut microbiota, and isn't something that can be stated as a single figure for either.
Taste and Mixability
Resistant dextrin is essentially flavourless and mixes into hot or cold liquid without changing the texture much, which is why it's a common base for powdered supplements intended to disappear into a drink. Psyllium is also largely flavourless, but its gelling means it visibly thickens whatever it's mixed into; this is a deliberate, useful property in some baking and cooking applications, and a texture some people have to get used to in a drink.
How Each Is Regulated as Dietary Fibre in Australia
Psyllium is a naturally occurring plant fibre that meets the Food Standards Code's dietary fibre definition (resistant to digestion in the small intestine, fermented in the large intestine, with the required polysaccharide structure) without needing a specific application to FSANZ. Resistant dextrin, as a manufactured ingredient, needed its status established through FSANZ Application A491, which assessed resistant maltodextrin against the Code's dietary fibre definition and an approved method of analysis before it could be declared as dietary fibre on an Australian label.
Low FODMAP Status
Monash University, the main Australian authority on FODMAP testing, hasn't published a specific low FODMAP serve threshold for either ingredient in a form we could verify directly. FODMAP status for a finished product depends on testing that specific product, including its serve size and any other ingredients, so a general ingredient-level description isn't a substitute for checking the product you're actually using.
Side by Side
| Psyllium | Resistant dextrin | |
|---|---|---|
| Source | Plantago ovata seed husk | Manufactured from starch |
| In water | Forms a gel | Dissolves clear |
| Taste | Neutral | Neutral |
| Australian regulatory route | Meets the general Code definition | FSANZ Application A491 |
Sources
- FSANZ, Final Assessment Report, Application A491, Resistant Maltodextrin as Dietary Fibre
- Effect of extraction temperature on the rheological properties of psyllium husk mucilage, PMC
- Molecular Structure and Properties of Resistant Dextrins from Potato Starch Prepared by Microwave Heating, PMC