Inulin / FOS
A soluble fibre from chicory root, best known for feeding gut bacteria.
- Keeping regular
- Feeding gut bacteria
- Blood sugar
- Appetite and fullness
- Weight and body fat
- Cholesterol
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is inulin / FOS?
Inulin is a soluble fibre that plants store as a chain of fructose units, and chicory root is the richest source and the one most supplements are made from. It is in some 36,000 plant species, onion, garlic, barley and Jerusalem artichoke among them. The short chains, two to ten units long, are sold as fructo-oligosaccharides, or FOS; the longer ones as inulin, and both come as powder or capsules. Manufacturers have long used it to stand in for fat or sugar, so it is already in many dairy and baked goods.
Why do people take inulin / FOS?
Keeping regular
The thinking. Hard or unpredictable bowel movements are the commonest reason people reach for a chicory fibre. Inulin passes through the small intestine undigested and reaches the colon intact, where the bacteria that feed on it multiply, so what leaves is wetter and there is more of it.
What research has found. Five randomised trials in 252 adults with long-standing constipation were pooled: how often people went, how firm the stool was and how long it took to pass all shifted in the fibre’s favour. Bloating and pain did not change. Research here is still young: a few studies so far, mostly pointing the same way.
Feeding gut bacteria
The thinking. Inulin is the fibre most often meant when a label says prebiotic: food not for you but for the bacteria already living in your large intestine. People buy it to shift that community rather than add to it.
What research has found. Reviews pooling dozens of trials, in healthy adults, older adults, children and adults with type 2 diabetes, counted bacteria in stool samples. Bifidobacterium, the group that takes it up most readily, rose consistently at 3 to 20 g a day, more so above 5 g and beyond four weeks. What the fatty acids themselves did was less consistent. This is one of the best-studied uses, and several reviews of trials broadly agree.
Blood sugar
The thinking. Blood sugar is another thing inulin is bought for in quantity, and the thinking follows the fermentation rather than the fibre itself: the fatty acids the bacteria make are absorbed, and researchers have followed them to see whether insulin works better.
What research has found. A pooling of 33 trials in 1,346 people, mostly adults with prediabetes or type 2 diabetes, found fasting glucose, HbA1c and fasting insulin lower on about 10 g a day. A second review found the picture less settled in adults without diabetes, and one 45-day trial found no change on inulin alone. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Appetite and fullness
The thinking. Some people take a spoonful before meals hoping to arrive at the table less hungry. The thinking is that a fibre still being fermented hours later keeps the gut occupied for longer; reviews list satiety among the things inulin has been measured for.
What research has found. A review of the adult trials found no effect on appetite scores, nor on how much people ate at a meal or across a day. A later 12-week trial in 125 adults carrying extra weight did record less hunger. Only a few studies have measured this so far, though they mostly agree.
Weight and body fat
The thinking. Chicory fibre turns up in slimming routines, usually alongside eating less rather than instead of it. The thinking runs partly through appetite and partly through the fibre itself, which fills space without adding much the body can absorb as energy.
What research has found. A pooling of 32 trials found body weight about a kilogram lower than placebo, with 1,184 people behind that figure, and smaller differences in body mass index, fat mass and waist measurement. Body fat percentage shifted only in trials running beyond eight weeks. A fair body of trials has looked at this, and most point the same way.
Cholesterol
The thinking. Soluble fibre and cholesterol is one of the older ideas on the supplement shelf, and inulin is counted among the fibres studied for it. Reviews describe the fatty acids made in the colon as acting beyond the gut as well as inside it.
What research has found. Two poolings of randomised trials, the larger covering 55 trials and 2,518 adults, found LDL cholesterol lower by a small amount and triglycerides with it, while the other measures showed little to no difference. The reviewers rated their own certainty in those figures as low to very low. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.
What does inulin / FOS do in the body?
Inulin is a chain of fructose units joined by a link human digestive enzymes cannot break. It passes the length of the small intestine unchanged and arrives in the large intestine intact, where the resident bacteria ferment it. Bifidobacterium is the group that responds most reliably, and that response is what reviews mean by a prebiotic effect.
Fermentation produces short-chain fatty acids: acetate, propionate and butyrate. These feed the cells lining the colon directly, and reviews describe them as taking part in how immune cells develop, and as acting beyond the gut as well as within it. That same ready fermentability is why wind and bloating are what the trials watch for. Chain length may matter too: FOS is the short form and inulin the long one, and reviews say too few trials compared them directly to tell.
What do people say about taking inulin / FOS?
These are anecdotes people have shared, not evidence.
What people like
- Three of these five threads sit in blood sugar communities, so steadier readings over months is the most common thing people report.
- Feeling fuller and more satisfied after meals comes up often, sometimes with modest weight loss that nobody puts down to it alone.
- Some say it is easy to live with once stirred into yoghurt or porridge, with no gut trouble at a small amount.
- Several like that it feeds bacteria they already have rather than adding new ones; a few mention more energy or better mood.
Common complaints
- Wind is by far the commonest complaint, raised in every thread where people had actually taken it, loudest in the first fortnight.
- Bloating and looser, more frequent stools come up nearly as often, especially where someone started on a large amount instead of building up.
- A minority describe a much stronger reaction, digestion feeling stalled or old gut symptoms returning, and those people stop taking it.
- Several find the powder sticky and oddly sweet, and awkward to dissolve; a couple went well above 20 g and regretted it.
How people take it
- Starting small and building up over weeks is the advice posters give each other most often, and what most describe doing themselves.
- One to two teaspoons a day is the usual amount, with a tablespoon or more only after months of working up.
- Most stir it into something rather than drink it alone: yoghurt, porridge, cereal, morning coffee, or baked into low-carb bread.
- A few take it alongside a probiotic; one suggests starting at a weekend, at home, while the wind settles down.
Read from these public discussions:
- Inulin food supplements (Diabetes Forum, 2016)
- Inulin (Blood Sugar Diet forum, 2016)
- Inulin (Diabetes Forum, 2017)
- What have probiotics/prebiotics done for you? (Mumsnet, 2023)
- Chronic Constipation (Mumsnet, 2025)
What forms of inulin / FOS are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Inulin / FOS | Chains of fructose units from chicory root; short chains are sold as FOS, longer ones as inulin. | 5 g |
What else is worth knowing about inulin / FOS?
- Wind and bloating are the side effect these trials watch for: inulin ferments readily, which reviews link to bloating and flatulence, and one lists gut symptoms among its reported drawbacks. In the pooled FOS trials that measured them, symptoms were no more common than on the comparator at 2.5 to 15 g a day; the constipation trials found bloating and pain unchanged.
- One review puts the amount healthy adults tolerate at 10 g a day of native inulin, or 5 g of an inulin-rich chicory extract. Trials used 3 to 20 g a day for four weeks or more; labels give the amount per serving, which may be several capsules.
- In one trial in 150 adults, most of the gut-bacteria and metabolic changes were absent in people already taking metformin for type 2 diabetes; another found the bigger shift in people who already ate plenty of fibre.
- The trials ran in healthy adults, adults carrying extra weight, adults with type 2 diabetes, adults aged 55 to 80, and children aged 7 to 15.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (31 studies)
- Effectiveness of inulin intake on indicators of chronic constipation; a meta-analysis of controlled randomized clinical trials. (2014, meta-analysis)
- Effect of inulin, galacto-oligosaccharides, and polyphenols on the gut microbiota, with a focus on Akkermansia muciniphila . (2024, meta-analysis)
- Effect of chicory-derived inulin-type fructans on abundance of Bifidobacterium and on bowel function: a systematic review with meta-analyses. (2023, meta-analysis)
- The Prebiotic Potential of Inulin-Type Fructans: A Systematic Review. (2022, systematic review)
- Effect of Fructooligosaccharides Supplementation on the Gut Microbiota in Human: A Systematic Review and Meta-Analysis. (2022, meta-analysis)
- The effects of inulin on gut microbial composition: a systematic review of evidence from human studies. (2020, systematic review)
- Enhancing gut microbiota and microbial function with inulin supplementation in children with obesity. (2024, randomised trial)
- Flexibility of Gut Microbiota in Ageing Individuals during Dietary Fiber Long-Chain Inulin Intake. (2021, randomised trial)
- Link between gut microbiota and health outcomes in inulin -treated obese patients: Lessons from the Food4Gut multicenter randomized placebo-controlled trial. (2020, randomised trial)
- Prebiotic effect of inulin-type fructans on faecal microbiota and short-chain fatty acids in type 2 diabetes: a randomised controlled trial. (2020, randomised trial)
- A prospective randomized, double-blind, placebo-controlled, dose-response relationship study to investigate efficacy of fructo-oligosaccharides (FOS) on human gut microflora. (2019, randomised trial)
- Habitual dietary fibre intake influences gut microbiota response to an inulin-type fructan prebiotic: a randomised, double-blind, placebo-controlled, cross-over, human intervention study. (2018, randomised trial)
- Prebiotic inulin-type fructans induce specific changes in the human gut microbiota. (2017, randomised trial)
- Inulin-type fructans modulate intestinal Bifidobacterium species populations and decrease fecal short-chain fatty acids in obese women. (2015, randomised trial)
- Agave Inulin Supplementation Affects the Fecal Microbiota of Healthy Adults Participating in a Randomized, Double-Blind, Placebo-Controlled, Crossover Trial. (2015, randomised trial)
- Effect of Inulin-Type Carbohydrates on Insulin Resistance in Patients with Type 2 Diabetes and Obesity: A Systematic Review and Meta-Analysis. (2019, meta-analysis)
- Inulin-type fructans supplementation improves glycemic control for the prediabetes and type 2 diabetes populations: results from a GRADE-assessed systematic review and dose-response meta-analysis of 33 randomized controlled trials. (2019, meta-analysis)
- Dietary supplementation with inulin-propionate ester or inulin improves insulin sensitivity in adults with overweight and obesity with distinct effects on the gut microbiota, plasma metabolome and systemic inflammatory responses: a randomised cross-over trial. (2019, randomised trial)
- The prebiotic inulin improves substrate metabolism and promotes short-chain fatty acid production in overweight to obese men. (2018, randomised trial)
- Effect of Butyrate and Inulin Supplementation on Glycemic Status, Lipid Profile and Glucagon-Like Peptide 1 Level in Patients with Type 2 Diabetes: A Randomized Double-Blind, Placebo-Controlled Trial. (2017, randomised trial)
- Effects of inulin-type fructans on appetite, energy intake, and body weight in children and adults: systematic review of randomized controlled trials. (2013, systematic review)
- Inulin-type fructans and whey protein both modulate appetite but only fructans alter gut microbiota in adults with overweight/obesity: A randomized controlled trial. (2017, randomised trial)
- The effects of chicory inulin-type fructans supplementation on weight management outcomes: systematic review, meta-analysis, and meta-regression of randomized controlled trials. (2024, meta-analysis)
- The effects of inulin-type fructans on cardiovascular disease risk factors: systematic review and meta-analysis of randomized controlled trials. (2024, meta-analysis)
- Effect of inulin-type fructans on blood lipid profile and glucose level: a systematic review and meta-analysis of randomized controlled trials. (2017, meta-analysis)
- Inulin: Properties, health benefits and food applications. (2016, review)
- Immunomodulatory effects of inulin and its intestinal metabolites. (2023, review)
- Inulin: properties and health benefits. (2023, review)
- Inulin fructans in diet: Role in gut homeostasis, immunity, health outcomes and potential therapeutics. (2022, review)
- Inulin, a flexible oligosaccharide I: Review of its physicochemical characteristics. (2015, review)
- Functional and therapeutic potential of inulin: A comprehensive review. (2019, review)
How much does inulin / FOS cost?
That depends on the form and the pack, so we work out the price of the same dose of every inulin / FOS product we can find and rank them.