What Is Inulin? Foods, Prebiotic Fibre and Side Effects

Inulin is a soluble, fermentable fibre made of chains of fructose, stored in the roots and bulbs of certain plants: chicory root is richest at 36 to 48 g per 100 g, then Jerusalem artichoke (16 to 20 g), garlic (9 to 16 g), leeks (3 to 10 g) and onions (1 to 7.5 g), with small amounts in wheat and bananas.^{1, 2}

Sources checked on 30 October 2026.

American diets provide about 2.6 g of inulin and 2.5 g of oligofructose a day, about 70% from wheat and 25% from onions.¹ One GB wording is authorised, at 12 g of native chicory inulin a day; "prebiotic" and gut-health wordings were refused, so this page gives the trial numbers: 3 to 20 g a day raised bifidobacteria across 50 trials of 2,525 people, and wind is the usual price.^{3, 5, 6} Inulin is the fermenting fibre in the Wellgard fibre guide.

What is inulin, and is it the same as chicory root fibre, FOS and oligofructose?

Inulin is the general name for fructans, chains of fructose with a glucose at the end. Native inulin averages nine or more units a chain; oligofructose, also called fructo-oligosaccharides or FOS, is the short-chain version. "Chicory root fibre" on a label is inulin extracted from chicory root, the source of almost all commercial inulin; the three names describe one ingredient at different chain lengths.² Unlike psyllium it forms no gel; it passes the small intestine undigested and is fermented in the colon. That makes it a fermentable, non-viscous fibre and a FODMAP (the fructan "O"): it changes the bacteria and makes gas.⁷

Which foods are high in inulin?

Food tables rarely list inulin because standard fibre methods do not measure it; these ranges come from the two surveys that analysed foods directly, per 100 g fresh weight.^{1, 2}

The ranges are wide because inulin falls as a bulb is stored and with cooking; on a plate, Jerusalem artichokes, garlic, leeks and onions lead.^{1, 2} Which foods are high in fibre has the total-fibre table.

What is a prebiotic fibre, and is inulin good for you?

The 2017 international consensus defines a prebiotic as a substrate selectively used by the host's microorganisms that confers a health benefit; all prebiotics are fibre but most fibre is not prebiotic, and inulin and FOS are the best-studied examples.⁸ That they change the bacteria is well shown: across 50 trials in 2,525 people, chicory inulin-type fructans at 3 to 20 g a day raised bifidobacteria by a large margin (standardised mean difference 0.83).⁵ What that does for a person is less clear; bowel function improved at 12 g in constipated adults.⁴ Across 33 trials, inulin-type fructans lowered fasting glucose and HbA1c overall, more in prediabetes and type 2 diabetes (HbA1c 0.58 points, fasting glucose 0.6 mmol/L), and the authors' dose-response analysis pointed to 10 g a day for six weeks or more.⁹ Eggs, Greek yoghurt and meat are not prebiotics: they contain no fibre.¹⁵

What does the GB register let a label say about inulin?

One sentence. "Chicory inulin contributes to normal bowel function by increasing stool frequency" is authorised for foods providing at least 12 g a day of native chicory inulin, with the consumer told that the effect needs 12 g a day.³ At that dose, in a 2017 supplier-funded crossover trial, 44 constipated adults took 4 g three times a day for four weeks and went from a median three stools a week to four; a 2025 supplier-funded crossover trial of 39 adults on the same 12 g found larger gains in stool frequency and symptoms than placebo.^{4, 10} Wordings for "prebiotic", "bifidogenic", digestive health, fullness, calcium or magnesium absorption and bone density were refused, and no blood-sugar wording is authorised.³ A gummy's label states its inulin milligrams; the register's 12 g condition is the yardstick.

What are the side effects of inulin, and how do you build up?

Wind, then bloating, both dose-dependent. In a trial of 26 healthy adults given single doses, up to 10 g of native inulin and up to 5 g of oligofructose were well tolerated, while 10 g of oligofructose in one go substantially raised symptoms.⁶ People with IBS do not make more gas: on MRI, 40 g of inulin raised colonic gas as much in 29 healthy controls, but 13 of 29 with IBS reached their symptom threshold, against six after glucose, because their gut felt the distension more.¹¹ So a low-FODMAP diet excludes inulin by design, people with IBS and bloating are the likeliest to feel worse, and a healthy adult can start at 2 to 5 g a day and step up weekly, a practice rule rather than trial evidence, splitting 12 g into three doses as the 2017 trial did.⁴ If you are pregnant, breastfeeding or taking medication, ask your GP before adding an inulin supplement. See a GP, the NHS says, if constipation is not improving, if there is blood in your poo, or if your bowel habit has suddenly changed.¹²

Is inulin better than psyllium, and can you take them together?

They do different jobs. Psyllium forms a gel, is barely fermented and adds little gas; chicory inulin increased stool frequency at 12 g.^{4, 7} What psyllium husk does and psyllium, chia or flaxseed set the gel-formers out. An inulin gummy's label states its grams per serving, and they count towards the 30 g fibre target. Expect some wind at first if fermentable fibre is new to you, though up to 10 g of native inulin in one dose was well tolerated in the 26-adult trial.⁶ Do fibre gummies work compares gummy types by grams.

What we don't know

Whether long-chain inulin moves the bowel at all: across 47 publications only short-chain fructans raised stool frequency.¹⁶ What the rise in bifidobacteria does for a healthy person, beyond the bowel-function effects seen in healthy subjects.⁵ How much inulin a cooked or stored onion or leek still holds, since storage and cooking lower it.²

Frequently asked questions

Will inulin spike blood sugar?

Inulin itself passes the small intestine undigested, so it adds no sugar to the blood; a gummy's label lists any sugars it also contains. In prediabetes and type 2 diabetes, inulin-type fructans lowered fasting glucose by about 0.6 mmol/L across trials.^{7, 9}

What is inulin powder, and how much a day is safe?

Extracted chicory inulin, a fine powder that dissolves in drinks. The trials ran at 12 g a day for four weeks; wind is the limit.^{4, 6}

Does inulin reduce belly fat?

Across 55 trials, waist size changed little; in the 36 that weighed people, body weight was 0.97 kg lower, with low certainty and larger effects in overweight and obese adults; no weight claim is authorised.¹³

Does prebiotic fibre help with diarrhoea?

Inulin has no trial for it here. Gel-forming psyllium can firm loose stools, and in a trial of 39 adults with incontinence of loose stools, psyllium or gum arabic halved the share of incontinent stools against placebo.^{7, 14}

Sources

1. Moshfegh AJ, et al. Presence of inulin and oligofructose in the diets of Americans. Journal of Nutrition, 1999. Analysis of a US government dietary survey, over 15,000 people; US Department of Agriculture authors. PubMed 10395608.
2. van Loo J, et al. On the presence of inulin and oligofructose as natural ingredients in the western diet. Critical Reviews in Food Science and Nutrition, 1995. Narrative review with food analyses; authors employed by an inulin producer. PubMed 8777017.
3. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. Statutory register. gov.uk.
4. Micka A, et al. Effect of consumption of chicory inulin on bowel function in healthy subjects with constipation. International Journal of Food Sciences and Nutrition, 2017. Randomised placebo-controlled crossover trial, 44 adults, 4 weeks per arm; supplier-funded, two authors at an inulin supplier's institute. PubMed 27492975.
5. Nagy DU, et al. Effect of chicory-derived inulin-type fructans on abundance of Bifidobacterium and on bowel function. Critical Reviews in Food Science and Nutrition, 2023. Meta-analysis, 50 trials, 2,525 people; first author at an inulin supplier's institute. PubMed 35833477.
6. Bonnema AL, et al. Gastrointestinal tolerance of chicory inulin products. Journal of the American Dietetic Association, 2010. Randomised crossover trial, 26 healthy adults, single doses; non-government support listed on PubMed, no grant record. PubMed 20497775.
7. McRorie JW, McKeown NM. Understanding the physics of functional fibers in the gastrointestinal tract. Journal of the Academy of Nutrition and Dietetics, 2017. Narrative review; government and non-government support listed on PubMed. PubMed 27863994.
8. Gibson GR, et al. ISAPP consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology and Hepatology, 2017. Expert consensus statement. PubMed 28611480.
9. Wang L, et al. Inulin-type fructans supplementation improves glycemic control for the prediabetes and type 2 diabetes populations. Journal of Translational Medicine, 2019. Meta-analysis, 33 randomised trials, 1,346 people; public funding (China), no conflicts declared. PubMed 31805963.
10. Puhlmann ML, et al. Inulin-induced improvements on bowel habit and gut microbiota in adults with functional constipation. BMC Gastroenterology, 2025. Randomised placebo-controlled crossover trial, 39 adults, 4 weeks per arm; funded by an inulin supplier, which employs two authors. PubMed 41233756.
11. Major G, et al. Colon hypersensitivity to distension, rather than excessive gas production, produces carbohydrate-related symptoms in individuals with irritable bowel syndrome. Gastroenterology, 2017. Randomised crossover study, 29 adults with IBS and 29 controls; Medical Research Council funding. PubMed 27746233.
12. NHS. Constipation. Page last reviewed 26 October 2023 (review due 26 October 2026). nhs.uk.
13. Talukdar JR, et al. The effects of inulin-type fructans on cardiovascular disease risk factors. American Journal of Clinical Nutrition, 2024. Meta-analysis, 55 randomised trials, 2,518 adults; authors' grants from public bodies and food-industry groups listed. PubMed 38309832.
14. Bliss DZ, et al. Supplementation with dietary fiber improves fecal incontinence. Nursing Research, 2001. Randomised placebo-controlled trial, 39 adults, 31 days; US National Institutes of Health funding. PubMed 11480529.
15. Public Health England. McCance and Widdowson's Composition of Foods Integrated Dataset (CoFID), 2021. Food composition dataset. gov.uk.
16. de Vries J, et al. Effects of β-fructans fiber on bowel function: a systematic review and meta-analysis. Nutrients, 2019. Meta-analysis of 47 publications; funded by a fructan supplier that employed two authors. PubMed 30621208.

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This article is general information, not medical advice.