Yeast mannan

Also called YM, yeast cell-wall mannan, yeast mannans.

Best grade C across 5 graded outcomes Other Last checked Oct 21, 2026

The short answer

From 4 sources

Yeast mannan is a fibre from the yeast cell wall studied as a prebiotic. Two Japanese placebo-controlled trials at 1.1 g a day, both with authors from the company group that makes it, reported more frequent bowel movements, more Bacteroides gut bacteria and less subjective skin dryness, with deep-sleep changes in one. An open-label study found 15 g a day well tolerated.

Every graded outcome on this page

5 rows · line = participants

Grade CGut bacteria, putrefactive compounds and bowel habitsGut microbiomen 100
Grade CSubjective skin drynessSkinn 100
Grade DDefecation frequency and stool volumeBowel habitsn 40
Grade DDeep sleep measured by EEGSleepn 40
Grade DStool frequency and gut symptoms in older adultsBowel habitsn 20

Key facts

Bowel habits: 1.1 g/day raised defecation frequency and stool volume vs placebo in 40 adults with defecation discomfort¹
Gut bacteria: In 100 women, 8 weeks raised Bacteroides thetaiotaomicron and B. ovatus and lowered fecal p-cresol, indole and skatole vs placebo²
Tolerance: 15 g/day for 2 weeks in 20 older adults caused only slight increases in cramping and bloating³
Conflicts of interest: Both placebo-controlled trials had authors employed by Asahi Quality and Innovations and used yeast mannan made from Asahi Group Foods yeast cell walls; the open-label study had Lallemand co-authors^1,2,3

What it is

Yeast mannan is an indigestible, water-soluble polysaccharide from the yeast cell wall, studied as a prebiotic fibre.

How it works

Proposed

Yeast mannan passes undigested to the colon, where in trials it selectively increased Bacteroides species and lowered putrefactive compounds. In the sleep trial, changes in fecal propionate and GABA were statistically linked to sleep changes; whether they cause them is not established.^1,2,3

Forms, side by side

2 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.

Yeast mannan forms compared

2 forms

Yeast mannan forms compared: 2 forms by 3 attributes. Empty cells are labelled No data yet, or Not graded in the evidence row.
2 forms	Tablets (1.1 g/day)	Powder (15 g/day)
Absorption in people	Indigestible; it reaches the colon, where gut bacteria ferment it.²	Indigestible; in a lab gut simulation it produced less gas than inulin.³
GI tolerance	No side effects observed over 8 weeks in 110 women.²	Slight increases in cramping and bloating over 2 weeks in older adults.³
Studied for	Bowel habits, gut bacteria, skin dryness, sleep	Gut tolerance and stool frequency

Yeast mannan tablets (1.1 g/day)
Absorption in people
Indigestible; it reaches the colon, where gut bacteria ferment it.²
GI tolerance
No side effects observed over 8 weeks in 110 women.²
Studied for
Bowel habits, gut bacteria, skin dryness, sleep
Yeast mannan powder (15 g/day)
Absorption in people
Indigestible; in a lab gut simulation it produced less gas than inulin.³
GI tolerance
Slight increases in cramping and bloating over 2 weeks in older adults.³
Studied for
Gut tolerance and stool frequency

What the human research says

Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.

Trial map

5 graded outcomes, largest study first

5 graded outcomes: 4 improved, 1 mixed. The largest, a 2020 randomized trial of 100 people on gut bacteria, putrefactive compounds and bowel habits, found an improvement.

By ageBy sizeTable

AgeAll ages

Bar: the ages a study enrolled (running to the edge when it states no upper or lower limit). Dot: only a mean age, counted as near your age within 5 years. Tick: the mean age inside a range.

3Defecation frequency and stool volume: improved, 22–64

4Deep sleep measured by EEG: improved, 22–64

1Gut bacteria, putrefactive compounds and bowel habits: improved, 30–49

2Subjective skin dryness: improved, 30–49

5Stool frequency and gut symptoms in older adults: mixed, mean age 71

1Gut bacteria, putrefactive compounds and bowel habits

Improved · Grade C · RCT, 100 people, 2020

Healthy women aged 30-49 (Japan)

Dose, result and source

Every graded outcome on this page, largest study first
Outcome	Found	People	Study	Who was studied
Gut bacteria, putrefactive compounds and bowel habits	Improved	100	Grade C · RCT, 2020	Healthy women aged 30-49 (Japan)
Subjective skin dryness	Improved	100	Grade C · RCT, 2020	Healthy women aged 30-49 (Japan)
Defecation frequency and stool volume	Improved	40	Grade D · RCT, 2023	Healthy adults aged 22-64 with discomfort in defecation (Japan)
Deep sleep measured by EEG	Improved	40	Grade D · RCT, 2023	Healthy adults aged 22-64 with discomfort in defecation (Japan)
Stool frequency and gut symptoms in older adults	Mixed	20	Grade D · Open-label trial, 2025	Older adults, mean age 71 (Florida, US)

Every graded row

5 rows

Form tested

Showing 5 of 5 outcomes. Human trials only.

Grade CGut bacteria, putrefactive compounds and bowel habitsGut microbiomeMore Bacteroides, fewer putrefactive compoundsRCT
n 100 · 2020

Improved Bacteroides thetaiotaomicron and B. ovatus rose, fecal p-cresol, indole and skatole fell and urinary equol rose vs placebo. Defecation days per week rose more than with placebo; stool form scores did not differ. No side effects were observed.

Design: RCT, n = 100, 2020
Population: Healthy women aged 30-49 (Japan)
Form: Yeast mannan tablets vs maltose placebo
Dose: 1.1 g/day (0.62 g mannan)
Duration: 8 weeks
Source: Reference 2 · PubMed 33260560 (opens PubMed)

Grade CSubjective skin drynessSkinLess self-rated drynessRCT
n 100 · 2020

Improved Skin-dryness scores after 8 weeks were lower with yeast mannan than placebo; itching scores did not differ.

Design: RCT, n = 100, 2020
Population: Healthy women aged 30-49 (Japan)
Form: Yeast mannan tablets vs maltose placebo
Dose: 1.1 g/day
Duration: 8 weeks
Source: Reference 2 · PubMed 33260560 (opens PubMed)

Grade DDefecation frequency and stool volumeBowel habitsMore frequent bowel movementsRCT
n 40 · 2023

Improved Defecation frequency and stool volume increased significantly more than with placebo.

Design: RCT, n = 40, 2023
Population: Healthy adults aged 22-64 with discomfort in defecation (Japan)
Form: Yeast mannan vs placebo
Dose: 1.1 g/day
Duration: 4 weeks
Source: Reference 1 · PubMed 38201970 (opens PubMed)

Grade DDeep sleep measured by EEGSleepMore deep sleep vs placeboRCT
n 40 · 2023

Improved After 4 weeks, time in deep (N3) sleep was higher and N3 latency shorter than with placebo, and time in bed was longer.

Design: RCT, n = 40, 2023
Population: Healthy adults aged 22-64 with discomfort in defecation (Japan)
Form: Yeast mannan vs placebo
Dose: 1.1 g/day
Duration: 4 weeks
Source: Reference 1 · PubMed 38201970 (opens PubMed)

Grade DStool frequency and gut symptoms in older adultsBowel habitsOverall change not significantOpen-label trial
n 20 · 2025

Mixed Stool frequency trended up from 1.35 to 1.53 a day (P = .079); in the 8 people with 1 or fewer stools a day it rose from 0.84 to 1.19 (P = .016). Most gut symptoms did not change; cramping and bloating rose slightly.

Design: Open-label trial, n = 20, 2025
Population: Older adults, mean age 71 (Florida, US)
Form: Yeast mannan powder, no control group
Dose: 15 g/day
Duration: 2 weeks after a 1-week baseline
Source: Reference 3 · PubMed 40117931 (opens PubMed)

What the numbers add up to

Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.

One maker behind the controlled trials

Both placebo-controlled trials had authors employed by an Asahi group company and used yeast mannan made from Asahi Group Foods yeast cell walls; independent replication is lacking.^1,2

Studied doses

Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.

Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.

Doses studied in human trials

Doses studied in human trials ranged from 1.1 g/day for 4-8 weeks in Japanese placebo-controlled trials to 15 g/day for 2 weeks in an open-label study. These are research doses, not recommendations.^1,2,3

Interactions and safety

Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.

Interactions

0 agents

None found in our sources.

Check with what you take

Kept on this device only

Add what you take. We list every interaction our evidence profiles cite between Yeast mannan and your picks, and between your picks.

Add a supplement or medicine

Most cited:

Add a supplement or medicine you take to check it against Yeast mannan.

Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.

Who should be careful

3 groups

People prone to bloating: At 15 g/day, cramping and bloating rose slightly from baseline in older adults.³
People on medicines: No drug-interaction studies have been published, so effects with sedatives, diabetes drugs, blood thinners or other medicines are unknown.^1,2,3
Pregnancy and breastfeeding: NCCIH notes that many dietary supplements have not been tested in pregnant women or nursing mothers, and no yeast mannan trial reported results in them. LactMed has no yeast mannan entry, so there are no breastfeeding data.⁴

Frequently asked questions

Short answers to common questions; the numbers link to the sources below.

Common questions

6 answers

Does yeast mannan help with regularity?

Two small Japanese trials found more frequent bowel movements than placebo at 1.1 g/day. In an open-label US study at 15 g/day the overall change was not significant, though people with infrequent stools improved.^1,2,3

Does it improve sleep?

One 40-person trial measured more deep sleep with an EEG device after 4 weeks. Participants were not chosen for sleep problems, and the result has not been replicated.¹

Does it cause gas?

At 15 g/day for 2 weeks, cramping and bloating rose only slightly, and in a lab gut model it produced less gas than inulin.³

Does yeast mannan interact with medicines?

No interaction studies or case reports have been published, and the trials did not report any. NCCIH notes that dietary supplements in general may interact with medicines, so the absence of data is not proof of safety.^4,1,2,3

Is it the same as glucomannan?

No. Yeast mannan comes from the yeast cell wall, while glucomannan is a different fibre from konjac and has its own page.

What is yeast mannan?

An indigestible, water-soluble polysaccharide from the yeast cell wall that gut bacteria ferment, so it is studied as a prebiotic.²

Sources

4 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.

Sources cited on this page

4 sources

1Effects of Prebiotic Yeast Mannan on Gut Health and Sleep Quality in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Study.RCT Nutrients, 2023 · PMID 38201970
2Effects of Yeast Mannan Which Promotes Beneficial Bacteroides on the Intestinal Environment and Skin Condition: A Randomized, Double-Blind, Placebo-Controlled Study.RCT Nutrients, 2020 · PMID 33260560
3Yeast mannans promote laxation and specifically modulate microbiota composition in older adults: An open-label pilot study.Open-label trial Nutr Res, 2025 · PMID 40117931
4Using Dietary Supplements WiselyFact sheet National Center for Complementary and Integrative Health (NCCIH), 2019 · nccih.nih.gov

What changed

Every dated change to this page: what changed, who made it and why.

Change log

3 entries

Dated changes to this page
Date	Change	Who and why
Oct 21, 2026who should be careful, FAQ	A–Z audit. Interaction check: no yeast mannan entry in LactMed or LiverTox (NCBI archives searched) and no interaction studies or case reports in PubMed, so the interactions list stays empty; added an FAQ saying so and a note that LactMed has no entry. PubMed search 2020 to 2026 found no human trials beyond the three already graded (PMIDs 33260560, 38201970, 40117931). NCCIH page reopened.	Writer: Kymata Health EditorialTrigger: A–Z page audit
Oct 14, 2026who should avoid	Pregnancy and breastfeeding caution re-sourced to NCCIH (agency source) instead of trial reports	Writer: Kymata Health EditorialTrigger: adversarial review
Oct 14, 2026all	Initial editorial evidence review	Writer: Kymata Health EditorialTrigger: new page

Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.