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Prebiotics

Carbohydrates that gut microbes use as fuel, such as inulin and GOS. Studied for gut bacteria, bloating, constipation and markers of inflammation.

Strongest evidenceGut healthStrong, 281 studies
Median dose in studies7,400 mg a dayFrom 247 study groups
Dose in trials on bloating2.75 to 3.5 g a dayOf GOS, in 2 small trials. Inulin did not reduce bloating.
Dose in trials on inflammation10 g a dayFor 8 to 12 weeks, in 3 trials of blood markers.
Ask a doctor or pharmacist first

Ask a doctor or pharmacist first if you:

  • have irritable bowel syndrome: the same dose gave these people more symptoms than healthy people[1]
  • have inflammatory bowel disease: 12 g a day of fructans made symptoms worse in people in remission who had gut symptoms[2]
  • have a food allergy, especially to artichoke or to GOS: severe reactions to inulin and to GOS have been reported[3][4]
  • take diabetes medicine: inulin-type fructans lowered blood sugar in people with prediabetes or type 2 diabetes[5]
  • are pregnant or breastfeeding: a review found no serious concerns, but another found only 1 prebiotic study among 27 in pregnancy[6][7]
  • plan to give a prebiotic to a child: a Cochrane review asked for more research before routine use to prevent allergy in formula-fed infants[8]

Overview

What are prebiotics?

Prebiotics are substances that gut microbes use selectively, in a way that gives a health benefit.[9] Most are carbohydrates that the upper gut does not digest, and microbes use them as fuel.[10][11]

The main groups are fructans (inulin and fructo-oligosaccharides, or FOS), galacto-oligosaccharides (GOS), lactulose, resistant starch, polydextrose and pectin oligosaccharides.[10] They occur naturally in foods such as garlic, onion, chicory and asparagus. The amounts in food are low, so some are also made on a large scale and added to foods.[10] A 2025 British guideline on constipation accepted trials that gave fiber supplements, including prebiotic fiber, as pills, capsules, powder sachets, solutions or fortified foods and drinks.[12]

Prebiotics are different from probiotics, which are live microbes. Synbiotics contain both.[11]

What are prebiotics used for?

Prebiotics raise bifidobacteria, a group of gut bacteria, in many trials, but this does not always bring relief from symptoms.[13][14] The evidence differs from use to use:[13][15]

  • Bloating and gas: mixed. A 2019 review of 11 trials found no overall benefit. Flatulence improved at doses of 6 g a day or less and with types other than inulin-type fructans, and got worse with inulin-type fructans.[13]
  • Inflammation: a 2025 review of 90 trials found lower blood markers in adults, but about half of the prebiotic studies in a 2017 review found no drop.[15][16]
  • Gut health and constipation: EFSA concluded that 12 g a day of native chicory inulin raises stool frequency. A 2025 British guideline found that inulin-type fructans softened stools a little and did not change frequency.[17][12]
  • Immune support: 17 trials found fewer people with a respiratory infection, mostly infants and children, with less evidence in adults.[18]
  • Weight: a 2024 review of inulin-type fructans found about 1 kg less weight, with low certainty.[19]
  • Blood sugar: a 2019 review of 33 trials found lower fasting glucose and HbA1c in people with prediabetes or type 2 diabetes.[5]
  • Minerals: single trials found better absorption of calcium in adolescents and of iron from ferrous fumarate in women with low iron stores.[20][21]

Two other uses have little support. Reviews found no significant benefit in irritable bowel syndrome, or for depression.[22][23] For traveler's diarrhea, a 2017 guideline found the evidence insufficient for a recommendation.[24]

Are prebiotics safe?

Prebiotics are generally considered safe, but they can cause gas, bloating and diarrhea, more so at higher doses.[10] A 2023 Cochrane review covered 45 studies of synbiotics, prebiotics and probiotics in chronic kidney disease. Side effects were uncommon and mild, such as flatulence, nausea, diarrhea and abdominal pain, but they were poorly reported.[25]

Severe allergic reactions have been reported. A woman with an artichoke allergy had anaphylaxis, a severe allergic reaction, after foods with inulin.[3] Anaphylaxis to GOS in milk formula has been described in people with allergies in South-East Asia. A study at Singapore allergy clinics estimated that up to 3.5% of patients are allergic to one commercial GOS.[4]

No official upper limit for prebiotics was found in the NIH Office of Dietary Supplements and EFSA sources searched.[11][17] People with irritable bowel syndrome or inflammatory bowel disease, people with allergies and people who take diabetes medicine should ask a doctor or pharmacist first.[2][1][4][5]

How it works

Prebiotics act through gut bacteria. They travel to the colon, and microbes use them there.[16][10]

  1. Upper gut

    Prebiotics resist acids, protein-digesting enzymes and bile salts in the upper gut, and the body does not digest them.[10]

  2. Fermentation

    In the colon, bacteria ferment soluble prebiotic fibers.[16]

  3. More bifidobacteria

    Bifidobacteria rise. A 2019 review of 11 trials found higher counts in adults with functional bowel disorders.[13]

  4. Fatty acids

    Fermentation makes short-chain fatty acids such as acetate, propionate and butyrate. These can make the gut more acidic, change gut movement and act on immune cells.[10]

  5. Gas

    Fermentation also makes gas. A drink with 40 g of inulin raised gas and volume in the colon on MRI, in healthy people and in people with irritable bowel syndrome.[1]

Benefits and studies

Each row is one benefit. The square shows the grade and the number of studies. Open a row to see the most trusted studies.

StrongModerateWeakNo trials
BenefitMain effects in studiesStudiesPeople

Dose

Trials used different substances and amounts, so no single dose applies. Trials on bloating, inflammation and stool frequency gave about 3 to 12 g a day of a named prebiotic.[26][27][17] No official daily intake for prebiotics was found in the NIH Office of Dietary Supplements and EFSA sources searched.[11][17]

Usual dose

For bloating and gas: 2.75 g and 3.5 g a day of GOS.[26][28] For blood markers of inflammation: 10 g a day of inulin, resistant dextrin or a blend.[27][29][30] For stool frequency: 12 g a day of native chicory inulin.[17] For blood sugar: 10 g a day of inulin-type fructans.[5]

Form

Trials name the type, because the type changes the result: inulin, oligofructose, GOS or resistant dextrin.[13][31] A 2025 guideline accepted trials of fiber in pills, capsules, powder sachets, solutions and fortified foods or drinks.[12]

When to take

No trial found compared times of day. In women with low iron stores, 15 g of GOS raised iron absorption when taken together with ferrous fumarate, and not with ferrous sulfate.[21]

How long

Lower bloating scores appeared within 1 week in one trial.[26] A review of fiber supplements points to 4 weeks or more for stool frequency,[32] and a review of inulin-type fructans points to 6 weeks or more for blood sugar.[5] The 3 trials of inflammation markers above ran 8 to 12 weeks.[27][29][30]

Upper limit

No official upper limit was found in the NIH Office of Dietary Supplements and EFSA sources searched.[11][17] In one trial of healthy young adults, up to 10 g of native inulin and up to 5 g of oligofructose were well tolerated.[33] Women took about 15 g of GOS a day for 4 weeks in another trial.[21] Side effects rise with dose.[10] People with a sensitive gut, an allergy or diabetes should ask a doctor or pharmacist first.[1][4][5]

Doses in studies

Most studies gave 5,000 to 10,000 mg a day, for 1 to 3 months.

The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.

How much a day247 groups in 193 studies
  1. Up to 100 mg10 groups
  2. 100 to 250 mg6 groups
  3. 250 to 500 mg11 groups
  4. 500 to 1,000 mg8 groups
  5. 1,000 to 2,500 mg28 groups
  6. 2,500 to 5,000 mg45 groups
  7. 5,000 to 10,000 mg78 groups
  8. 10,000 to 25,000 mg47 groups
  9. 25,000 to 50,000 mg11 groups
  10. 50,000 mg or more3 groups
For how long241 groups in 187 studies
  1. 1 week or less12 groups
  2. 1 to 4 weeks85 groups
  3. 1 to 3 months115 groups
  4. 3 to 6 months21 groups
  5. 6 to 12 months8 groups
  6. More than a year0 groups
Half of the groups took less than 7,400 mg a day. Half took more.Half of the groups took 2,500 to 10,000 mg a day. A quarter took less, a quarter took more.220 of 247 groups took 500 mg a day or more. Do not copy a study dose without a doctor.

Taken together

97 of 247 study groups took prebiotics with something else. This shows what studies gave together, not what works together.

  1. Probiotics62 studies69
  2. Iron5 studies6
  3. Inulin4 studies4
  4. Zinc3 studies4
  5. Vitamin D3 studies3
  6. Yacon3 studies3
Bars and numbers count study groups. A companion is shown only when at least 3 different studies gave it.

Protocols

What studies used when they gave prebiotics for one goal, or to a group of people.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Questions

12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.

Basics
Which foods contain prebiotics?

Garlic, onion, chicory, asparagus, Jerusalem artichoke, tomatoes, wheat, barley and rye contain prebiotics.[10] The amounts in these foods are low, so some prebiotics are made on a large scale and added to products.[10] For inulin, the food industry often uses Jerusalem artichoke tubers and chicory roots.[34]

Open the answer with sources ›
Are prebiotics the same as fiber?

Not exactly. Most prebiotics are dietary fibers, but not all dietary fibers are prebiotics.[10] To count as a prebiotic, a substance must be used selectively by microbes, and a health benefit must be documented.[9]

This means results for fiber may not carry over. In a 2022 review of fiber for constipation, psyllium and pectin had significant effects.[32] In a 2025 British guideline, inulin-type fructans softened stools a little but did not raise stool frequency, and GOS and polydextrose changed neither.[12]

Open the answer with sources ›
Benefits
Do prebiotics help with bloating and gas?

Mostly no, and the result depends on the type and the dose. A 2019 review of 11 trials with 729 adults with irritable bowel syndrome or similar disorders found no overall benefit for bloating or flatulence.[13] Flatulence improved at 6 g a day or less and with types other than inulin-type fructans, and it got worse with inulin-type fructans.[13]

Two small trials of low-dose galacto-oligosaccharides (GOS), at 2.75 g and 3.5 g a day, did report less bloating.[26][28] Trials and reviews of inulin did not.[35][36]

Read the full answer ›
Do prebiotics reduce inflammation?

They lower some blood markers of inflammation in adults, but results vary. A 2025 review of 90 trials found lower C-reactive protein (CRP), TNF-α and IL-6 in adults who took prebiotics or synbiotics.[15] A 2021 review of 12 trials in people with overweight or obesity found CRP lower by 1.06 mg/L.[37]

The effect was inconsistent in healthy people,[38] and treatments aimed at gut bacteria showed no significant drop in older adults.[39] In a 2017 review, about half of the studies found a drop in at least 1 marker.[16]

Read the full answer ›
Do prebiotics help with irritable bowel syndrome?

Reviews do not support it so far. A 2019 review of 11 trials with 729 adults with irritable bowel syndrome or similar disorders found no benefit on overall response, pain, bloating, flatulence or quality of life.[13] A 2024 review found no significant improvement with prebiotics or synbiotics, and a 2023 review called their effect uncertain because of too few trials.[22][40]

One small trial in 44 people found that 3.5 g a day of GOS improved symptoms.[28] Some prebiotics can also make symptoms worse. In 29 people with irritable bowel syndrome, 13 reached the symptom threshold after 40 g of inulin, against 6 after glucose.[1] Clinical diets for this condition often limit these same substances as FODMAPs, a group of fermentable carbohydrates.[41]

Open the answer with sources ›
Do prebiotics help with constipation?

Somewhat, and the evidence conflicts. EFSA, the European food safety agency, concluded in 2015 that 12 g a day of native chicory inulin raises stool frequency, from 6 studies with 86 people.[17] In 2021 it found the evidence insufficient for a similar product, because one trial at 15 g a day had not been repeated.[42]

The newest guideline is more careful. A 2025 British guideline for chronic constipation found that inulin-type fructans softened stools a little and did not raise stool frequency, with low certainty. GOS and polydextrose changed neither.[12] A 2024 review of 37 trials found that lactulose added 3.39 bowel movements a week, with moderate certainty.[43]

In a 2022 review, fiber supplements as a whole helped: 66% responded, against 41% with control, mainly with psyllium and pectin at more than 10 g a day.[32]

Open the answer with sources ›
Do prebiotics help you lose weight?

Only slightly, if at all. For weight, a 2024 review of inulin-type fructans found 0.97 kg less body weight across 36 trials with 1672 people, with low certainty. The effect was larger in trials of 6 weeks or more, and in people with overweight or obesity.[19] An older 2021 review of 12 trials with 535 people with overweight or obesity found no drop in weight, BMI or fat mass.[37]

Open the answer with sources ›
Do prebiotics lower blood sugar and cholesterol?

A little, mainly in people whose blood sugar is already high. A 2019 review of 33 trials with 1346 people found that inulin-type fructans lowered fasting glucose by 0.60 mmol/L and HbA1c by 0.58% in people with prediabetes or type 2 diabetes. The authors favored 10 g a day for 6 weeks or longer.[5] A 2024 review of adults in general found little to no effect on these two measures.[19]

For cholesterol, the 2024 review of 55 trials found LDL cholesterol lower by 0.14 mmol/L, with very low certainty, and triglycerides lower by 0.06 mmol/L, with low certainty.[19]

Open the answer with sources ›
Do prebiotics prevent infections?

Possibly in infants and children, and less clearly in adults. For immune support, a 2022 review found fewer people with a respiratory infection across 17 prebiotic trials (odds ratio 0.73). Most trials were in infants and children, and evidence in adults was thinner.[18] A 2026 review of healthy people also found fewer infections in infants given GOS, FOS or 2'-fucosyllactose.[38]

In one trial of 142 hospital patients treated for Clostridium difficile diarrhea, relapse was 8.3% with oligofructose against 34.3% with placebo.[44] This result comes from a single trial. For traveler's diarrhea, a 2017 guideline found the evidence insufficient.[24]

Open the answer with sources ›
Safety
Can prebiotics make bloating and gas worse?

Yes, especially inulin-type fructans at higher doses and in people with a sensitive gut. A 2019 review found that inulin-type fructans made flatulence worse in functional bowel disorders.[13] In healthy adults, flatulence and then bloating were the most common symptoms after 5 g or 10 g of inulin products.[33] People with irritable bowel syndrome reported more symptoms than healthy people from the same dose.[1]

Read the full answer ›
Are prebiotics safe in pregnancy and for children?

In pregnancy and breastfeeding, no serious safety signal has appeared, but data are limited. A 2021 review of probiotics and prebiotics found no serious health concerns for mother or baby.[6] An earlier review found only 1 prebiotic study among the 27 studies in pregnancy.[7]

In infants, a 2013 Cochrane review of 4 studies with 1218 babies found less eczema with prebiotics in formula (risk ratio 0.68). All these studies had a high risk of attrition bias, meaning that many babies dropped out, and the authors said more research is needed before routine use.[8] Anaphylaxis to GOS in milk formula has been described in people with allergies in South-East Asia.[4] Kenyan infants received 3 g or 7.5 g a day of GOS and FOS in cereal for 3 weeks,[45] and adolescents received 8 g a day of inulin-type fructans for 1 year.[20] Ask a doctor or pharmacist before use in pregnancy or for a child.[6][8]

Open the answer with sources ›
Forms and timing
Which prebiotic has the best evidence: inulin, FOS or GOS?

It depends on the goal, and no type leads for everything. Low-dose GOS has the better results for gas and bloating, though from small trials.[26][28] Chicory inulin has the EFSA opinion on stool frequency.[17] Inulin-type fructans, which include FOS, have large reviews for blood sugar, cholesterol and weight.[5][19] They also made flatulence worse in a 2019 review.[13]

Read the full answer ›

References

  1. Colon Hypersensitivity to Distension, Rather Than Excessive Gas Production, Produces Carbohydrate-Related Symptoms in Individuals With Irritable Bowel Syndrome. Major G, Pritchard S, Murray K, Alappadan JP, Hoad CL, Marciani L, et al. Gastroenterology, 2017. PMID 27746233
  2. Fermentable Carbohydrates [FODMAPs] Exacerbate Functional Gastrointestinal Symptoms in Patients With Inflammatory Bowel Disease: A Randomised, Double-blind, Placebo-controlled, Cross-over, Re-challenge Trial. Cox SR, Prince AC, Myers CE, Irving PM, Lindsay JO, Lomer MC, et al. J Crohns Colitis, 2017. PMID 28525543
  3. Anaphylactic reaction to inulin: first identification of specific IgEs to an inulin protein compound. Franck P, Moneret-Vautrin DA, Morisset M, Kanny G, Mégret-Gabeaux ML, Olivier JL Int Arch Allergy Immunol, 2005. PMID 15650313
  4. Anaphylaxis to galacto-oligosaccharides--an evaluation in an atopic population in Singapore. Soh JY, Huang CH, Chiang WC, Llanora GV, Lee AJ, Loh W, et al. Allergy, 2015. PMID 25951913
  5. 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. Wang L, Yang H, Huang H, Zhang C, Zuo HX, Xu P, et al. J Transl Med, 2019. PMID 31805963
  6. Are Probiotics and Prebiotics Safe for Use during Pregnancy and Lactation? A Systematic Review and Meta-Analysis. Sheyholislami H, Connor KL Nutrients, 2021. PMID 34371892

Review history

  1. 4 Nov 2026CheckedReviewerChecked every claim against its source.
  2. 4 Nov 2026Page createdResearcherFirst edition, written from PubMed and public health sources.