Most adults in the UK eat about 20g of fibre a day. The government target is 30g.[1] That gap is why fibre supplements sell, and why two names keep turning up on the shelf: psyllium and inulin.
Both are fibre. They are not the same thing, and they don't do the same job.
Two fibres, two very different jobs
Psyllium is the husk of Plantago ovata seeds. Stir it into water and it swells into a thick gel. That gel is the whole trick: it holds water in the gut and adds soft bulk. We've covered how that works in more detail in our psyllium husk guide.
Inulin is a different animal. It comes from chicory root (and, in smaller amounts, onions, garlic and leeks), and it doesn't bulk anything. Your gut bacteria ferment it. That makes it a prebiotic, a food for the bugs rather than a sponge for water. If the prebiotic idea is new, probiotics vs prebiotics is the place to start.
One bulks. One feeds. Which you want depends on what you're actually trying to do.
What the constipation research shows
In 2025 the British Dietetic Association published guidelines on managing chronic constipation in adults through diet, built on four systematic reviews covering 75 randomised trials.[2] On the fibre supplement question, the picture was clear. Psyllium softened stools, increased how often people went and reduced straining, with the effects showing up at higher doses and over longer periods. Supplements based on inulin and similar fibres (polydextrose, galacto-oligosaccharides) didn't show the same benefit, and inulin-based ones made flatulence more likely.[2]
That's guidance for chronic constipation, not a promise about any one person's gut. But it's a useful steer: if regularity is the goal, psyllium has the stronger track record.
So why does inulin have an authorised claim?
Fair question, because it does. There's an authorised claim that chicory inulin contributes to normal bowel function by increasing stool frequency, with one condition attached: it needs a daily intake of 12g of native chicory inulin.[3]
Both things can be true. That authorisation is about a defined amount of one specific type of inulin, while the BDA looked across fibre supplements as a group. Twelve grams is also a lot to take in one go, so check the label on anything that mentions inulin and see whether an amount is given at all. Plenty don't.
Choosing between them
Reach for psyllium if the aim is softer, more regular stools. Think about inulin if you're more interested in feeding your gut bacteria than in bowel movements, and go slowly, since gas is the usual price of fermentable fibre.
Plenty of people want a bit of both, and that's the logic behind our Psyllium Husk Fibre: 4,200mg of psyllium husk fibre, with prebiotic inulin and live cultures alongside it. Psyllium does the bulking, the inulin is there for your gut bacteria, and the cultures go in with them.
To be straight about it: the trials behind the psyllium findings tended to use higher doses over longer periods, so treat 4,200mg as a steady top-up that sits alongside the fibre you eat, not a full-dose protocol. We also don't list an inulin amount, so we're not claiming the 12g effect for it.
Starting without regret
- Go low first — a sudden jump in any fibre is what causes the gas and bloating, so build up over a couple of weeks.
- Drink water with it — psyllium needs liquid to do its job, and more with each dose.
- Keep eating fibre — porridge, beans, lentils, wholemeal bread and vegetables with their skins on all count towards that 30g.
- Mention it to a pharmacist — if you take regular medication, ask how to space it from a fibre supplement.
If constipation is persistent, or comes with blood in your stools or a change in bowel habit that doesn't settle, see your GP rather than self-managing with supplements.
Good fibre habits are rarely dramatic. A bowl of porridge, a glass of water, a capsule or two, repeated for weeks. That's the standard worth holding yourself to.
Frequently asked questions
Is psyllium or inulin better for constipation?
On the current evidence, psyllium. The BDA's 2025 guidelines found psyllium softened stools and increased frequency, while inulin-based supplements didn't show a benefit and made flatulence more likely. Inulin is better thought of as a prebiotic than a bulking fibre.
Can you take psyllium and inulin together?
They're often combined in one product, and the two work differently, so there's no clash in principle. Start with a low dose, build up slowly and drink plenty of water. If you're curious how prebiotics and live cultures fit together, our guide to probiotics vs prebiotics explains it.
How long should you try a fibre supplement before judging it?
Longer than a few days. The BDA guidelines suggest starting at a low dose and persisting for at least four weeks before deciding whether it's helping. If nothing has improved, speak to your GP or pharmacist.
Why does fibre make me bloated?
Gut bacteria ferment some fibres, especially inulin, and gas is a by-product. Increasing too fast makes it worse. Going slowly gives your gut time to adjust, and the BDA review noted inulin-based supplements in particular raised the likelihood of flatulence.
Sources
- NHS — 30g a day fibre target and average UK adult intake of about 20g. https://www.nhs.uk/live-well/eat-well/digestive-health/how-to-get-more-fibre-into-your-diet/
- Dimidi E, van der Schoot A, Barrett K, et al. British Dietetic Association guidelines for the dietary management of chronic constipation in adults, Journal of Human Nutrition and Dietetics, 2025 — cited for psyllium and inulin findings and the low-dose, four-week trial suggestion. https://doi.org/10.1111/jhn.70133 (summary: News-Medical)
- Commission Regulation (EU) 2015/2314 (as retained in UK law) — authorised chicory inulin claim and 12g daily intake condition. https://www.legislation.gov.uk/eur/2015/2314/annex/adopted
At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.
