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Allen KamravaMD · MBA · FACS · FASCRS

Why is my poop so long?

In healthy adults, what determines stool length and shape (e.g., fiber intake, colonic transit time), and does a long stool indicate normal variation versus an underlying bowel problem?

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Evidence review in plain language · compiled 2026-10-13 · checked 2026-10-13 · next 2026-11-13 · automated review, how it works

What the evidence says

Bottom line

No study has directly looked at why healthy people's stools are long, or whether a long stool means something is wrong.

The 34 studies found are almost all trials of constipation treatments, or lab and microbiome studies; none set out to measure stool length itself. Related measures such as stool thickness, consistency, weight, and transit time have been studied — for example, more fibre softened stool, increased fecal weight, and shortened transit time in people without bowel dysfunction, and a small smart-toilet study linked slower stool passage to thicker stool — but no study has tested whether these relate to stool length, or whether a long stool signals an underlying bowel problem such as a stricture or mass.

How certain

Very low

The 30 human studies found measure a related question rather than this one, so they can only be read indirectly.

What it shows

Not studied

No study has measured this outcome in people with this condition.

studies found
34studies found
randomised trials
13randomised trials
people studied
20,984people studied
reviews of trials
3reviews of trials
years covered
2023–2026years covered
finished, never published
24finished, never published

What the research shows

  • Stool length and diameter measurements

    No study in this set measured stool length or diameter as an outcome. One very small smart-toilet study tracked stool thickness and how long it took to drop, but not length, and only in 11 people.[1]

    Not studied

  • Bristol stool form scale score

    Many trials measured the Bristol scale, which grades stool texture from hard lumps to watery — not length. These trials were done in people with constipation or IBS, not in people asking why a stool was long, so they cannot answer this question directly.[1,2,3,4,5,6,7,8,9,10,11,12]

    Insufficient evidence

  • Dietary fiber intake

    In people with normal bowel function, more fibre was linked to softer stool, more stool weight, and faster transit; a high-fibre diet was linked to better stool form in a small group of healthy women. Neither study measured stool length.[1,2]

    Possible improvement

  • Association with bowel pathology (e.g., stricture, mass)

    One small surgical case series looked at outcomes after surgery for anal narrowing (stenosis) that developed following hemorrhoid surgery — it did not test whether stool length predicts strictures or masses in otherwise healthy people. A separate study found that the Bristol Stool Scale (a stool-shape tool) was poor at identifying constipation in children, while a different constipation-symptom score was much more accurate; neither tested stool length as a predictor of structural bowel disease. No study has tested whether a long stool in an otherwise healthy person predicts a stricture, mass, or other bowel problem.[1,2]

    Not studied

What it may help with

  • In people with normal bowel function, higher fibre intake was linked to softer stool, more stool weight, more frequent bowel movements, and faster gut transit — though this evidence is based on statistical models across many measurements, not a head-to-head trial of long stools specifically.[1]
  • A small pilot study found that healthy women following a traditional high-fibre diet had better stool form than those on their usual diet after four weeks.[1]

Important limitations

  • Almost every study here was designed to test treatments for constipation or to study gut bacteria — none asked 'why is a stool long' or compared long stools with other lengths.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
  • The standard tool used in these studies, the Bristol stool form scale, grades texture (hard to watery) on a 1–7 scale. It does not measure length, and one study found it was a poor tool even for diagnosing constipation.[1]
  • The one study that measured stool size directly used a smart toilet with only 11 participants and no control for diet or hydration, so it cannot be generalised.[1]
  • Evidence on bowel narrowing and stool shape comes only from people who had already had surgery for a known problem, not from otherwise healthy people with a long stool.[1]

What the studies found

  • Found a benefit17 · 50%
  • Found no clear effect2 · 6%
  • Mixed or unclear15 · 44%

What kind of studies

  • Randomised trial13 · 38%
  • Prospective cohort5 · 15%
  • Case series4 · 12%
  • Retrospective3 · 9%
  • Laboratory study3 · 9%
  • Case-control2 · 6%
  • Meta-analysis2 · 6%
  • Systematic review1 · 3%
  • Animal study1 · 3%

The studies that decided it

  • Do et al. 2026

    Surgical management of anal stenosis following hemorrhoid treatment: a single-center case series

    Surgery fixed narrowed anus, not stool size.Case seriesLow qualityRelated question

    13 people13.3 months (range 6-24 months)

    12 of 13 patients had good outcomes, healing in about 2 months on average; 1 patient had the problem come back and needed another operation

    Who was studied
    patients with anal narrowing (stenosis) after hemorrhoid surgery
    What they received
    surgery to release the scar/fibrotic ring, sometimes combined with rectal tissue repair (mucosal advancement, suturing, or V-Y flap)
    Compared with
    different surgical techniques compared to each other (no untreated or non-surgical comparison group)
    Main outcome
    ability to pass stool normally, stool thickness, and absence of pain or bleeding after surgery
    Quality
    This is a small, uncontrolled case series of only 13 patients, so it cannot reliably prove the surgery caused the improvement.
    Limitations
    Small sample size, no comparison group, retrospective design, and it addresses anal narrowing after hemorrhoid surgery rather than the general question of long stool size.

    Taken word for word from the abstract

    • population 13 patients with anal stenosis after hemorrhoidectomy
    • intervention fibrotic ring release alone, fibrotic ring release with rectal mucosal advancement, fibrotic ring release with horizontal suturing of the rectal mucosa, and fibrotic ring release with V-Y flap reconstruction
    • comparator Patients treated with fibrotic ring release alone experienced the longest healing time, while those who underwent mucosal advancement or V-Y flap reconstruction had shorter recovery periods
    • primaryOutcome Outcomes were assessed based on patients' ability to achieve normal defecation, stool caliber, and the absence of anal pain or bleeding postoperatively
    • result Surgical outcomes were favorable in 12 out of 13 patients (92.3%), with an average healing time of 2.0 ± 1.1 months
    • n This retrospective case series included 13 patients with anal stenosis after hemorrhoidectomy

    Int J Colorectal Dis · PMID 41748755 · Read it on PubMed ↗

  • Balk et al. 2026

    Fiber intake and laxation in people with normal bowel function: a systematic review

    More fiber means bulkier, more frequent stools.Systematic reviewModerate qualityRelated question

    size not given2026

    more fiber modestly softened stool, increased fecal weight and frequency, and shortened gut transit time, with low-solubility, low-fermentability fibers having the strongest effects

    Who was studied
    healthy adults with normal bowel function
    What they received
    higher dietary fiber intake
    Compared with
    lower fiber intake or different fiber types
    Main outcome
    stool consistency, fecal weight, bowel movement frequency, and gut transit time
    Quality
    Based on many randomized trials with low-to-moderate bias, but the authors say findings come from indirect modeling rather than direct dose comparisons in most individual trials.
    Limitations
    The authors state findings are indirect, based on statistical models rather than direct trial comparisons, and that there is insufficient evidence in specific subpopulations.

    Taken word for word from the abstract

    • population general population without bowel dysfunction
    • intervention increasing fiber intake (per g/d total fiber)
    • comparator compared fiber amounts or types
    • primaryOutcome assessed stool consistency, fecal weight, fecal frequency, or gut transit time
    • result increasing fiber intake (per g/d total fiber) yields softening stool consistency [0.013 units, 95% credible interval (CrI): 0.009, 0.016 on the Bristol Stool Scale], increasing total fecal weight (1.76 g/d, 95% CrI: 1.58, 1.94) and dry fecal weight (0.47 g/d, 95% CrI: 0.42, 0.51), increasing fecal frequency (0.053 additional bowel movements/wk, 95% CrI: 0.042, 0.065), and shortening gut transit times (-0.24 h, 95% CrI: -0.36, -0.12)
    • limitations findings are indirect, based on models, and there is insufficient evidence in specific subpopulations

    Am J Clin Nutr · PMID 41611088 · Read it on PubMed ↗

  • Estevam de Abreu et al. 2026

    Beyond the Rome IV criteria: Diagnostic accuracy of clinical tools for functional constipation in children and adolescents

    Symptom scores help diagnose constipation accurately.Case seriesLow qualityRelated question

    106 people2026

    the constipation score tool was most accurate (92.1%), one voiding-symptom question was moderately accurate (72.5%), while stool shape scale and rectal diameter were poorly accurate (under 60%)

    Who was studied
    children and teenagers aged 4-17 being evaluated for possible constipation in pediatric and urology clinics
    What they received
    clinical scoring tools (Cleveland Clinic Constipation Score, Bristol Stool Scale, Dysfunctional Voiding Symptom Score, rectal diameter measurement) used to identify constipation
    Compared with
    official Rome IV diagnostic criteria for constipation (used as the gold standard)
    Main outcome
    how accurately each tool identified functional constipation compared to the Rome IV criteria
    Quality
    this was a cross-sectional comparison of scoring tools in a relatively small group, so it shows which tools match a diagnosis rather than why stools are long or what causes constipation.
    Limitations
    abstract does not describe blinding, how patients were selected beyond age range and clinic type, or any assessment of long-term outcomes.

    Taken word for word from the abstract

    • n This cross-sectional study included 106 patients aged 4-17 years
    • population evaluated in general pediatric and specialized lower urinary tract dysfunction outpatient clinics
    • intervention the pediatric-adapted Cleveland Clinic Constipation Score (CCS), the Bristol Stool Scale, the Dysfunctional Voiding Symptom Score (DVSS), and rectal diameter (RD)
    • comparator using the Rome IV criteria as the gold standard
    • primaryOutcome Each assessment tool was compared against the Rome IV criteria in terms of sensitivity, specificity, and overall accuracy.
    • result The CCS demonstrated the highest diagnostic accuracy (92.1 %), with a sensitivity of 89.5 % and specificity of 80.0 %
    • result Item 4 of the DVSS, which assesses the perception of effort during defecation, showed an accuracy of 72.5 %
    • result the Bristol Stool Scale (types 1 and 2), RD measurement, and DVSS item 3 (bowel movement frequency) presented low accuracy levels (<60 %)

    J Pediatr Urol · PMID 41193362 · Read it on PubMed ↗

  • Zhu et al. 2025

    Comprehensive microbial and clinical profiling of functional constipation: A stratified comparative study of age and constipation subtype

    Gut bacteria differ by age and constipation type.Case-controlLow qualityRelated question

    126 people2025

    Microbial diversity and composition differed significantly by age group and by constipation subtype (slow-transit vs defecatory disorder), with different bacteria linked to sphincter tone, peristalsis speed, and inflammation in each group

    Who was studied
    Adults with functional constipation (grouped by age: young, middle-aged, older) compared with healthy people without constipation
    What they received
    Gut microbiota profiling (16S rRNA sequencing) stratified by age group and constipation subtype, along with anorectal and transit testing
    Compared with
    Healthy control participants without constipation
    Main outcome
    Differences in gut microbial composition and their relation to constipation subtype, age, and anorectal/motility measurements
    Quality
    This is a small, non-randomized comparison of stool bacteria across groups, so it can show patterns but not prove what causes constipation or stool characteristics.
    Limitations
    Observational comparative study with limited sample size (92 patients, 34 controls); no intervention tested; does not address stool length or size specifically.

    Taken word for word from the abstract

    • n Ninety-two patients with FC completed questionnaires and underwent anorectal manometry and gastrointestinal transit tests; stool samples were collected for 16S rRNA gene sequencing. Stool samples alone were collected from 34 healthy controls.
    • population Patients with FC were categorized into age groups (young, middle-aged, and older) and classified into normal-transit constipation, slow-transit constipation (STC), defecatory disorder (DD), and mixed constipation subtypes.
    • intervention Gut microbial compositions across age groups and constipation subtypes were compared, and their correlations with clinical parameters were investigated.
    • comparator Stool samples alone were collected from 34 healthy controls.
    • primaryOutcome To characterize gut microbiota profiles by age and constipation subtype and identify factors associated with microbial composition in FC.
    • result Significant differences in microbial composition and function were observed across age groups and constipation subtypes in FC, suggesting underlying pathophysiological heterogeneity and providing a basis for precision diagnosis and treatment.

    World J Gastroenterol · PMID 41180988 · Read it on PubMed ↗

  • Song et al. 2025

    AI-Driven Defecation Analysis by Smart Healthcare Toilet: Exploring Biometric Patterns and Eu-Tenesmus

    Slower pooping linked to constipation, not length.Prospective cohortVery low qualityRelated question

    11 people2025

    Stools that took longer than 5 seconds to drop were linked to lower Bristol scores (more constipated), and stool thickness decreased as Bristol scores rose

    Who was studied
    11 people using a smart toilet system that tracked their bowel movements
    What they received
    smart toilet sensor monitoring of defecation behavior (stool duration, thickness, timing)
    Compared with
    stool consistency type measured by the Bristol Stool Form Scale
    Main outcome
    how stool dropping duration and thickness relate to stool consistency (constipation score)
    Quality
    Only 11 people and 45 bowel movements were studied using a new device, so the findings are preliminary and not yet validated.
    Limitations
    Very small number of participants and events, no mention of controlling for diet, hydration, or health conditions, and this is an exploratory technology-validation study rather than a clinical trial.

    Taken word for word from the abstract

    • n Analyzing 45 defecation events from 11 participants
    • population Analyzing 45 defecation events from 11 participants
    • intervention a smart toilet system is developed that enables real-time monitoring of defecation behaviors
    • comparator longer durations (>5 s) linked to lower Bristol Stool Form Scale (BSFS) scores
    • primaryOutcome key defecation parameters are identified, including stool dropping duration, stool thickness, and eu-tenesmus interval
    • result Stool dropping duration follows a log-normal distribution, with longer durations (>5 s) linked to lower Bristol Stool Form Scale (BSFS) scores, suggesting constipation (p = 0.008 for BSFS1/2/3 vs BSFS5/6/7). Stool thickness decreases with increasing BSFS scores (p = 5 × 10⁻⁶ for BSFS1/2/3 vs BSFS5/6/7)

    Adv Sci (Weinh) · PMID 40349171 · Read it on PubMed ↗

  • Sun et al. 2024

    Consistency of Feces Affects Defecatory Function

    Harder stool is harder to pass.Laboratory studyLow qualityRelated question

    12 people2024

    harder simulated stool took longer and needed more pressure to pass than softer stool, with little difference beyond a certain hardness

    Who was studied
    healthy adult volunteers (10 analyzed, 4 female/6 male, ages 20-48)
    What they received
    simulated artificial feces of varying hardness inserted into the rectum
    Compared with
    different stool consistencies compared to each other (softer vs harder simulated stool)
    Main outcome
    measures of defecation such as duration, pressure needed, and shape changes during evacuation
    Quality
    Very small study using artificial stool in healthy volunteers, not real patients or real stool, so it may not reflect everyday bowel habits.
    Limitations
    Small sample size, one subject excluded for technical issues, used a mechanical device with simulated (not real) stool in healthy subjects rather than patients.

    Taken word for word from the abstract

    • population Twelve normal subjects were recruited for studies with the simulated feces device
    • n Twelve normal subjects were recruited
    • intervention The Fecobionics probes were inserted in rectum in random order with +20 minutes between insertions.
    • comparator Most differences were observed between the 0A and 10A probe
    • primaryOutcome duration, maximum bag pressure, duration x maximum bag pressure, and relaxation of the front pressure and the bend angle during evacuation
    • result the duration was 9 (8-12) seconds at 0A and 18 (12-21) seconds at 10A (P < 0.05), and maximum bag pressure was 107 (96-116) cmH2O at 0A and 140 (117-162) cmH2O at 10A (P < 0.05)

    J Neurogastroenterol Motil · PMID 38533644 · Read it on PubMed ↗

  • Minnebo et al. 2023

    Gut microbiota response to in vitro transit time variation is mediated by microbial growth rates, nutrient use efficiency and adaptation to in vivo transit time

    Slower gut transit changes bacteria, raises fermentation.Laboratory studyVery low qualityRelated question

    6 people2023

    transit time was the biggest factor changing bacterial growth and the mix of species; slower transit increased some fibre-digesting bacteria and overall short-chain fatty acid output, while faster transit let bacteria convert carbs to biomass more efficiently

    Who was studied
    stool bacteria samples from six people with short, medium or long gut transit times
    What they received
    growing those gut bacteria in an artificial gut model set to different transit speeds (21, 32 or 63 hours)
    Compared with
    the same bacteria samples grown at the other transit speeds
    Main outcome
    changes in bacterial growth, species makeup and the chemicals (short-chain fatty acids) they produce
    Quality
    this was a small lab experiment using an artificial gut model with only six stool donors, not a study of people or of stool size itself
    Limitations
    in vitro artificial gut model, only six donors, does not measure stool size or volume at all

    Taken word for word from the abstract

    • n faecal microbial communities from six individuals
    • population faecal microbial communities from six individuals with either short, medium or long in vivo transit times
    • intervention three different colonic transit times of 21, 32 and 63 h in the validated human gut in vitro model, SHIME
    • comparator three different colonic transit times of 21, 32 and 63 h
    • primaryOutcome Transit time was identified as the single most important driver of microbial cell concentrations (52%), metabolic activity (45%) and quantitative (24%) and proportional (22%) community composition.
    • result These microbial communities reached a higher population density and net carbohydrate fermentation, leading to an increased SCFA production at longer transit times. In contrast, the carbohydrate-to-biomass production efficiency was increased at shorter transits

    Microbiome · PMID 37926855 · Read it on PubMed ↗

All 34 studiesEvery study that answered the question, with its design, size and result.
The other 27 studiesEverything else the search returned, including anything retracted.

  • Gao et al. 2026

    Clinical efficacy of repetitive transcranial magnetic stimulation combined with electroacupuncture at Baliao points for functional constipation: a retrospective study

    More bowel movements with combined therapy.RetrospectiveLow qualityRelated question

    142 people8 weeks

    After 8 weeks, bowel movements increased more with combined therapy than with acupuncture alone (median 4 vs 3 per week, p<0.001), with better symptom, quality-of-life and transit-time scores

    Who was studied
    Adults with functional constipation treated at one hospital
    What they received
    Transcranial magnetic stimulation combined with electroacupuncture at Baliao points
    Compared with
    Electroacupuncture alone
    Main outcome
    Weekly number of complete bowel movements
    Quality
    It was a retrospective, non-randomized study without blinding or a sham control, so the findings are only exploratory.
    Limitations
    Given the absence of randomization, sham control and blinding, the findings should be interpreted as exploratory and hypothesis-generating

    Taken word for word from the abstract

    • n observation group (rTMS combined with EA, n = 67)
    • n control group (EA alone, n = 75)
    • population FC patients treated at a single hospital from February 2022 to March 2025
    • intervention adding repetitive transcranial magnetic stimulation (rTMS) to electroacupuncture (EA) at Baliao points
    • comparator control group (EA alone, n = 75)
    • primaryOutcome The primary outcome was weekly complete spontaneous bowel movements (CSBMs)
    • result After 8 weeks, CSBMs increased more in the observation group (week-8 median 4.00 vs. 3.00; p < 0.001)
    • limitations Given the absence of randomization, sham control and blinding, the findings should be interpreted as exploratory and hypothesis-generating
    • followUp After 8 weeks

    Front Neurol · PMID 42553215 · Read it on PubMed ↗

  • Can et al. 2026

    Effects of a Supervised Telerehabilitation-Based Exercise Program on Constipation Symptoms and Quality of Life in Adults With Chronic Constipation: A Randomized Controlled Trial

    Exercise program improved stool form, less constipation.Randomised trialLow qualityRelated question

    32 people4 weeks

    intervention group had more normal stool form, lower constipation severity scores, and better satisfaction scores than control at 4 weeks

    Who was studied
    adults with chronic constipation
    What they received
    supervised telerehabilitation exercise program plus online education
    Compared with
    online education alone
    Main outcome
    stool consistency and constipation severity scores
    Quality
    Very small trial of only 32 people over just 4 weeks, with the authors themselves calling the findings preliminary and needing confirmation.
    Limitations
    Small sample size, short follow-up, no objective physiological outcomes measured, authors state findings are preliminary and need confirmation in larger trials

    Taken word for word from the abstract

    • n telerehabilitation-based exercise plus online education group (n = 16) or an online education-only control group (n = 16)
    • population Adults with chronic constipation
    • intervention supervised telerehabilitation-based exercise plus online education group
    • comparator online education-only control group
    • primaryOutcome Outcomes included stool consistency assessed by the Bristol Stool Form Scale, constipation severity assessed by the Constipation Assessment Scale (CAS) and Constipation Severity Instrument (CSI)
    • result By Week 4, normal stool form (Bristol Types 3-5) was observed in 68.8% of the intervention group and 37.5% of the control group. CAS scores were lower in the intervention group at Week 4 (3.56 ± 2.94 vs. 7.25 ± 4.33; p = 0.008).

    Neurogastroenterol Motil · PMID 42186252 · Read it on PubMed ↗

  • Bhattacharya et al. 2026

    Exploring the Impact of Yoga on Autonomic Nervous System Function, Social Functioning, and Quality of Life in People with IBS

    Not relevant to stool length.Randomised trialLow qualityRelated question

    202 people3 months

    yoga group had reduced resting heart rate, improved heart rate variability ratio, increased Valsalva ratio, and better quality of life scores

    Who was studied
    adults aged 18-45 with irritable bowel syndrome (IBS)
    What they received
    3-month yoga program
    Compared with
    control group (no yoga)
    Main outcome
    autonomic nervous system function and quality of life
    Quality
    this study measured autonomic function and quality of life, not stool characteristics like length, so it doesn't answer the question about why someone's poop is long.
    Limitations
    abstract does not mention stool form, size, or bowel habit changes specifically; focuses on autonomic and quality of life measures.

    Taken word for word from the abstract

    • population The study included 202 people (ages 18-45) diagnosed with IBS according to the Rome IV criteria.
    • intervention a 3-month yoga intervention on IBS management
    • comparator control group (n = 100)
    • primaryOutcome to measure autonomic function and quality of life
    • result The yoga group showed significant improvements in autonomic function, with reductions in resting heart rate (p < 0.0001) and the low- to high-frequency ratio of heart rate variability (p < 0.0001), as well as an increase in the Valsalva ratio (p = 0.0100).
    • n The study included 202 people

    Int J Yoga Therap · PMID 42128431 · Read it on PubMed ↗

  • Park et al. 2026

    Effects of a spore-forming probiotic blend on bowel habits and physical well-being in adults with functional constipation: A randomized, double-blind, placebo-controlled trial

    Probiotic eased constipation symptoms.Randomised trialModerate qualityRelated question

    78 people4 weeks

    probiotic group had significant improvements in bowel symptoms and shifted stool consistency toward normal types

    Who was studied
    adults with functional constipation
    What they received
    spore-forming probiotic blend (Clostridium butyricum, Weizmannia coagulans, Bacillus subtilis)
    Compared with
    placebo
    Main outcome
    changes in weekly bowel movements and stool form
    Quality
    it was a randomized double-blind placebo-controlled trial but with a small sample size and only 4 weeks of follow-up
    Limitations
    abstract does not mention limitations such as small sample size or short duration explicitly, though the study design has these inherent constraints

    Taken word for word from the abstract

    • n 78 adults with FC (Rome IV criteria) received either probiotic blend (n = 40) or placebo (n = 38)
    • population adults with functional constipation (FC)
    • intervention spore-forming probiotic blend containing Clostridium butyricum IDCC 1301, Weizmannia coagulans IDCC 1201, and Bacillus subtilis IDCC 1101
    • comparator In a randomized, double-blind, placebo-controlled trial, 78 adults with FC (Rome IV criteria) received either probiotic blend (n = 40) or placebo (n = 38) daily for 4 weeks.
    • primaryOutcome Primary outcomes were changes in weekly spontaneous bowel movements (WSBM) and stool form.
    • result The probiotic blend group showed significant improvements in irritant bowel movements (p = 0.0458), incomplete evacuation (p = 0.0374), and abdominal pain before defecation (p = 0.0090). Stool consistency shifted toward normal types (Bristol types 3-4, p = 0.0176).

    PLoS One · PMID 42030329 · Read it on PubMed ↗

  • Hoang Van et al. 2026

    Effects of fermented milk containing Lacticaseibacillus paracasei strain Shirota on constipation and gut microbiota: A randomised pilot study in Vietnam

    Probiotic milk eased hard stools.Randomised trialLow qualityRelated question

    51 people4 weeks

    Probiotic group had significantly fewer hard/lumpy stools, more frequent stools, and less constipation on questionnaire scores compared to control

    Who was studied
    Vietnamese adults with constipation and hard or lumpy stools
    What they received
    fermented milk with Lacticaseibacillus paracasei strain Shirota probiotic, one bottle daily for 4 weeks
    Compared with
    no intervention (control group)
    Main outcome
    proportion of participants with hard or lumpy stools in 25% or more of bowel movements over 4 weeks
    Quality
    This was a small, open-label pilot study without a placebo or blinding, so bias and small numbers limit confidence in the results.
    Limitations
    Open-label design (no blinding), single-centre, small sample size, control group received no intervention rather than a placebo

    Taken word for word from the abstract

    • n 51 participants with HLS were randomised
    • population constipated Vietnamese adults with a high prevalence of HLS
    • intervention one bottle per day of fermented milk containing ≥6.5 × 109 cfu of LcS for 4 weeks (probiotic group)
    • comparator no intervention (control group)
    • primaryOutcome The primary endpoint was the proportion of participants with HLS (Bristol Stool Form Scale score of 1 or 2) in ≥25% of bowel movements over 4 weeks.
    • result the probiotic group had a significantly lower proportion of participants with HLS in ≥25% of bowel movements compared to controls (odds ratio: 0.00; 95% confidence interval: 0.00-0.16; P = 0.005)
    • result The probiotic group also showed increased total stool frequency ( P = 0.001), reduced HLS frequency ( P = 0.035), and fewer participants with CCQ scores ≥5 indicating constipation ( P < 0.001) at 4 weeks.

    Benef Microbes · PMID 41980711 · Read it on PubMed ↗

  • Seven Avuk et al. 2025

    The investigation of fermented food consumption on gastrointestinal symptoms: a cross-sectional study in university students

    More fermented foods linked to fewer GI symptoms.RetrospectiveLow qualityRelated question

    546 people2025

    Students who ate more yogurt, kefir, vinegar, cheese, and pickles had fewer gastrointestinal symptoms, and those with normal stool consistency had fewer symptoms than those with constipation

    Who was studied
    university students who completed a survey
    What they received
    frequency of eating fermented foods like yogurt, kefir, vinegar, cheese, pickles, sourdough bread
    Compared with
    different frequencies of fermented food consumption among students
    Main outcome
    gastrointestinal symptoms (bloating, pain, reflux) and stool consistency
    Quality
    This is a one-time survey of students' habits, not a controlled trial, so it can only show a link, not prove fermented foods cause fewer symptoms or affect stool length.
    Limitations
    Cross-sectional, self-reported food frequency questionnaire and symptom scales; cannot establish cause and effect.

    Taken word for word from the abstract

    • n included 546 university students
    • population university students
    • intervention FFs consumption habits were recorded using a food frequency questionnaire
    • comparator Significant differences were found between the frequency of yogurt, kefir, vinegar, cheese, pickle consumption, and gastrointestinal symptoms
    • primaryOutcome collecting data on sociodemographic characteristics, the Gastrointestinal Symptom Rating Scale (GSRS), and the Bristol Stool Form Scale (BSFS)
    • result Students with normal stool consistency had fewer dyspepsia, abdominal pain, reflux symptoms, and overall gastrointestinal symptoms than those with constipation (p < 0.05).

    PeerJ · PMID 41424727 · Read it on PubMed ↗

  • Malekiantaghi et al. 2025

    Abdominal massage as an adjunctive therapy for pediatric functional constipation: a randomized controlled trial

    Less constipation and leakage, not stool consistency.Randomised trialLow qualityRelated question

    61 people2025

    No significant difference in stool consistency between groups, but the massage group had a greater reduction in constipation severity scores and fewer fecal incontinence episodes

    Who was studied
    children aged 4 to 10 years with chronic functional constipation
    What they received
    abdominal massage (12 sessions) added to standard constipation medication
    Compared with
    standard constipation medication alone
    Main outcome
    stool consistency, constipation severity, and fecal incontinence episodes
    Quality
    Small trial of 61 children with short-term outcomes and no mention of blinding, so results need confirmation in larger studies.
    Limitations
    Abstract notes larger, multicenter trials are needed to confirm findings; no blinding described.

    Taken word for word from the abstract

    • n This randomized controlled trial included 61 children aged 4-10 years
    • population 61 children aged 4-10 years (mean age 6.36 ± 1.77) diagnosed with functional constipation
    • intervention the intervention group, receiving 12 sessions of Swedish abdominal massage involving effleurage and gentle pressing, vibration of the small and large intestines, kneading of the abdomen, and clockwise circular movements in addition to drug treatment
    • comparator the control group, receiving standard drug therapy
    • primaryOutcome Outcomes assessed included stool consistency (using the Bristol Stool Scale), constipation severity (measured by the Constipation Assessment Scale), and associated symptoms.
    • result Both groups showed improvements in stool consistency; however, no statistically significant difference was found between them. The intervention group demonstrated a significantly greater reduction in constipation symptoms (Constipation Assessment Scale scores decreased from 14.70 ± 1.29 to 10.21 ± 1.45, P < 0.001.) and fewer episodes of fecal incontinence (from 3.82 ± 1.33 to 2.70 ± 1.33 days/week, P < 0.001) compared to the control group.

    Turk J Pediatr · PMID 41327986 · Read it on PubMed ↗

  • Rausch et al. 2025

    First insights into microbial changes within an Inflammatory Bowel Disease Family Cohort study

    Gut bacteria linked to bowel transit time.Prospective cohortLow qualityRelated question

    size not given2025

    Community gradients correspond strongly with IBD pathologies, physiological manifestations of inflammation (e.g. Bristol stool score, ASCA IgA, ASCA IgG), and genetic risk for IBD. Anthropometric and medical factors influencing fecal transit time strongly modify bacterial communities.

    Who was studied
    IBD patients and their relatives, a population at high risk for IBD development
    What they received
    none - observational collection of microbial, health and lifestyle data over time (no treatment given)
    Compared with
    external IBD cohorts used for validation of findings
    Main outcome
    factors influencing the gut microbiota in health and IBD disease, including dysbiosis patterns
    Quality
    This is an observational cohort study of IBD patients and relatives looking at microbiome patterns, not a controlled study designed to explain why stool is long.
    Limitations
    Abstract does not report participant numbers, follow-up duration, or statistical details, and focuses on IBD-specific microbial dysbiosis rather than stool length in general.

    Taken word for word from the abstract

    • population index IBD patients and their relatives, a population at high risk for IBD development
    • intervention systematically and extensively collect data and biosamples from index IBD patients and their relatives
    • comparator strong and generalizable gradients within and across different external IBD cohorts for validation
    • primaryOutcome characterize the factors influencing the microbiota in health and disease via detailed ecological analyses
    • result These community gradients correspond strongly with IBD pathologies, physiological manifestations of inflammation (e.g. Bristol stool score, ASCA IgA, ASCA IgG), and genetic risk for IBD.
    • result Anthropometric and medical factors influencing fecal transit time strongly modify bacterial communities.

    Gut Microbes · PMID 41047557 · Read it on PubMed ↗

  • Akçalı et al. 2025

    A randomized trial of inulin for bowel symptoms, depression and quality of life in constipation predominant IBS

    Eased constipation symptoms in IBS.Randomised trialLow qualityRelated question

    34 people8 weeks

    IBS quality of life score rose and symptom severity score fell in the inulin group, with improved constipation and psychological state ratings

    Who was studied
    adults aged 21 to 63 with constipation-predominant IBS
    What they received
    inulin/oligofructose prebiotic supplement
    Compared with
    maltodextrin placebo
    Main outcome
    bowel symptoms, quality of life, and depression scores
    Quality
    This was a small, single-blind trial of only 34 people over just 8 weeks, so the results are an early signal rather than strong proof.
    Limitations
    small sample size, single-blind design (not double-blind), short 8-week intervention period

    Taken word for word from the abstract

    • n Individuals (n = 34) aged between 21 and 63 years with constipation-predominant IBS were included in the study
    • population Individuals (n = 34) aged between 21 and 63 years with constipation-predominant IBS were included in the study
    • intervention the prebiotic group (n = 17), which received a 50%/50% mixture of inulin/oligofructose (4.6 g twice daily, for a total daily dose of 9.2 g)
    • comparator the placebo group (n = 17), which total received 9.2 g of maltodextrin per day
    • primaryOutcome This study was conducted to evaluate the effect of inulin on bowel symptoms, depression and quality of life in individuals with constipation-predominant irritable bowel syndrome
    • result total IBS-QoL score increased in the prebiotic group (61.0 ± 19.4 to 77.4 ± 15.1; p < 0.006), whereas total IBS-SSS score decreased (267.3 ± 56.0 to 195.8 ± 59.0; p < 0.026)
    • followUp The intervention period was 8 weeks

    Sci Rep · PMID 41034384 · Read it on PubMed ↗

  • Aatsinki et al. 2025

    Early life gut microbial and metabolic shifts reflected in stool consistency- a gut transit time proxy

    Breastfeeding and gut bacteria shape infant stool firmness.Prospective cohortLow qualityRelated question

    618 people2025

    breastfeeding had the strongest association with stool consistency and water content, and certain bacterial metabolites (bile acid amidates, SCFAs) were linked to firmer or looser stools

    Who was studied
    infants and young children aged 2.5 to 30 months from a birth cohort study
    What they received
    breastfeeding status (exclusive vs partial) and gut microbial/metabolite composition
    Compared with
    partial versus exclusive breastfeeding
    Main outcome
    stool water content and parent-reported stool consistency
    Quality
    This is an observational, correlational study in infants from a preprint that has not yet been peer reviewed, so its findings are preliminary and not about adults or stool length specifically.
    Limitations
    Preprint not peer-reviewed; observational/correlational design; studies infants aged 2.5-30 months, not adults; does not address stool length specifically.

    Taken word for word from the abstract

    • n 618 stool samples
    • population 618 stool samples from children aged 2.5 months (n = 360), 6 months (n = 229), 14 months (n = 274), and 30 months (n = 169) from the FinnBrain Birth Cohort Study
    • intervention breastfeeding had the strongest association with both stool consistency and fecal water content
    • comparator Partial versus exclusive breastfeeding was further linked to higher levels of specific bile acid amidates through mediation by constipation
    • primaryOutcome correlating these data with stool water content and parent-reported stool consistency
    • result We found that breastfeeding had the strongest association with both stool consistency and fecal water content.

    bioRxiv · PMID 41000790 · Read it on PubMed ↗

  • Culqui Lévano et al. 2025

    Impact of prebiotics and postbiotics in the management of constipation: Analysis of their differentiated modulation of intestinal microbiota

    Improved stool consistency with prebiotic supplementRandomised trialLow qualityRelated question

    24 peopletwo weeks

    significant improvement in stool consistency after taking NextDext™ from constipated to normal, with only a trend toward improvement after ABB C24

    Who was studied
    adults with constipation
    What they received
    a dextran prebiotic (NextDext™) or a prebiotic-postbiotic combination (ABB C24)
    Compared with
    the two supplement types compared against each other
    Main outcome
    stool consistency (Bristol Stool Form Scale) and gut microbiome composition
    Quality
    Very small study (24 people) over just two weeks, which limits how much confidence can be placed in the results.
    Limitations
    Abstract does not report dropout, blinding success, or statistical details beyond 'significant' and 'trend'; sample size is very small.

    Taken word for word from the abstract

    • n 24 subjects with constipation
    • population subjects with constipation
    • intervention NextDext™, a dextran prebiotic, or ABB C24, a prebiotic-postbiotic combination of NextDext™ and ABB C22®, for two weeks
    • comparator double-blind, randomized and parallel-arm clinical study
    • primaryOutcome to evaluate their effects on stool consistency (Bristol Stool Form Scale) and gut microbiome
    • result a significant improvement in stool consistency after taking NextDext™ from constipated to normal (Bristol Scale) and a trend to improvement after ABB C24 supplementation
    • followUp for two weeks

    Clin Nutr ESPEN · PMID 40780410 · Read it on PubMed ↗

  • Ryu et al. 2025

    Multiomics insights into functional constipation: Exploring microbiome, metabolome, and lipidome independent of transit time

    Altered gut bacteria and metabolites in constipation.Case-controlLow qualityRelated question

    size not given2025

    certain gut bacteria and metabolites differed between constipation patients and healthy controls, but lipid levels did not differ before and after laxative use

    Who was studied
    patients with functional constipation and healthy controls
    What they received
    fecal sampling before and after laxative administration
    Compared with
    healthy controls
    Main outcome
    differences in gut microbiome, metabolome, and lipidome profiles
    Quality
    This is a small exploratory lab-style profiling study without a reported sample size, so its findings are not yet reliable evidence.
    Limitations
    No participant numbers given, and the abstract does not address stool length or size, only microbiome/metabolome/lipidome composition.

    Taken word for word from the abstract

    • population fecal samples were collected from patients with FC both before and after laxative administration
    • intervention fecal samples were collected from patients with FC both before and after laxative administration to minimize the impact of intestinal transit time
    • comparator Beneficial microbiota such as Anerobutyricum hallii, Blautia luti, Blautia wexlerae, Collinsella aerofaciens, and Fusicatenibacter saccharivorans were predominantly found in healthy controls (HC)
    • primaryOutcome These samples underwent comprehensive microbiome, metabolome, and lipidome analyses to discern the unique properties of FC.
    • result Beneficial microbiota such as Anerobutyricum hallii, Blautia luti, Blautia wexlerae, Collinsella aerofaciens, and Fusicatenibacter saccharivorans were predominantly found in healthy controls (HC), while harmful microbiota, Blautia faecis, was prevalent in patients with FC.
    • result In terms of lipidome profiling, no significant differences in lipid levels were observed between pre- and post-laxative FC samples.

    Dig Liver Dis · PMID 40713395 · Read it on PubMed ↗

  • Sahran et al. 2025

    Effects of Traditional Asian Diet on dietary fibre requirement, gut microbiome composition, and faecal and urine metabolomes in healthy Asian women: a pilot study

    High-fibre diet improved stool formRandomised trialLow qualityRelated question

    22 peoplefour-week

    higher fibre intake, lower fat intake, and better stool form with the Traditional Asian Diet compared to control

    Who was studied
    healthy Asian women
    What they received
    Traditional Asian Diet (high fibre diet program)
    Compared with
    control diet
    Main outcome
    meeting fibre needs, gut microbiome, faecal/urine chemicals, and stool form
    Quality
    This was a very small, short, pilot trial (11 per group over 4 weeks), so its findings are not very reliable on their own.
    Limitations
    Small pilot study with only 11 participants per group, short 4-week duration, and only healthy women studied, so findings may not generalize.

    Taken word for word from the abstract

    • n TAD group (n = 11) following a newly developed TAD program and the control group (n = 11)
    • population healthy Asian women
    • intervention Traditional Asian Diet (TAD)
    • comparator control group
    • primaryOutcome This study investigated TAD's effects on meeting fibre requirements, gut microbiome, and faecal and urine metabolomes.
    • result The TAD group showed significant increases in dietary fibre ( P < 0.001), reduced fat ( P < 0.05), and improved faecal form ( P = 0.009) compared to the control group.

    Benef Microbes · PMID 40312033 · Read it on PubMed ↗

  • Song et al. 2024

    Efficacy of acupuncture for functional constipation in elderly: a systematic review and meta-analysis

    Mixed results for constipation relief.Meta-analysisLow qualityRelated question

    469 people2024

    Acupuncture improved some constipation measures (treatment effectiveness, complete spontaneous bowel movements, Bristol Stool Scale, CCS) but showed no significant difference in spontaneous bowel movements, Defecation Difficulty Score, or PAC-QOL

    Who was studied
    elderly people with functional constipation
    What they received
    acupuncture treatment for constipation
    Compared with
    control group (standard care/medication)
    Main outcome
    treatment effectiveness and bowel movement measures (e.g., complete spontaneous bowel movements, Bristol Stool Scale, Clinic Constipation Score)
    Quality
    The authors themselves state the evidence is low-to-moderate quality and call for more high-quality research.
    Limitations
    Small number of trials (8 RCTs, 469 participants) with mixed outcome significance and author-acknowledged low-to-moderate quality evidence.

    Taken word for word from the abstract

    • n A total of 469 elderly individuals were included in 8 RCTs.
    • population elderly patients dealing with functional constipation
    • intervention the application of acupuncture has significantly elevated the rates of treatment effectiveness compared to the control group
    • comparator Compared with the control group, the treatment group exhibited a statistically significant difference in complete spontaneous bowel movements after treatment.
    • primaryOutcome the treatment group exhibited a statistically significant difference in complete spontaneous bowel movements after treatment
    • result The two groups showed no significant difference in spontaneous bowel movements. However, there was a significant difference in the Bristol Stool Scale scores.
    • result The Defecation Difficulty Score and Patient Assessment of Constipation Quality of Life (PAC-QOL) showed p-values that indicated no significant effect.

    Front Med (Lausanne) · PMID 39697209 · Read it on PubMed ↗

  • Nassar et al. 2024

    Impact of L-carnitine supplementation on gastric emptying and bowel function in pediatric ketogenic diet therapy: a clinical trial

    More frequent, easier bowel movements.Randomised trialLow qualityRelated question

    30 people3 months

    L-carnitine group had longer antral length, better stool consistency scores, and more frequent bowel movements than the diet-only group

    Who was studied
    children aged 12 months to 18 years with drug-resistant epilepsy starting a ketogenic diet
    What they received
    ketogenic diet plus L-carnitine supplement
    Compared with
    ketogenic diet without L-carnitine
    Main outcome
    stomach emptying speed (measured as antral length) and bowel habits
    Quality
    Very small trial (30 children) over just 3 months in a specific epilepsy population, not patients with everyday constipation or stool-size concerns.
    Limitations
    Small sample size, short 3-month duration, and population limited to children with drug-resistant epilepsy on a strict ketogenic diet rather than general bowel complaints.

    Taken word for word from the abstract

    • n The current study recruited 30 patients aged 12 months to 18 years
    • population newly diagnosed with DRE assigned to start KD who were following up at the Pediatric Clinical Nutrition and Neurology Outpatient Clinics
    • intervention arm I: received KD with L-carnitine supplementation
    • comparator arm II: received KD only
    • primaryOutcome The primary aim of the current clinical trial was to study the effect of L-carnitine supplementation on gastric emptying
    • result There was significant increase in antral length in the patients who received KD with L-carnitine supplementation compared to the non-supplemented group.
    • result L-carnitine supplementation to children with DRE on KD has a significant role in improving gastric motility and it increases the frequency of defecation.
    • followUp Patients were assessed at baseline and after 3 months of starting KD

    Sci Rep · PMID 39543202 · Read it on PubMed ↗

  • Letourneau et al. 2024

    Interplay between particle size and microbial ecology in the gut microbiome

    Gut bacteria shape food particle size.Laboratory studyLow qualityRelated question

    76 people2024

    Fecal particle size varied a lot between people but was not changed by better chewing or by diet; it was linked instead to gut transit time and to the mix of gut bacteria, and mice without gut bacteria had larger fecal particles than mice with normal bacteria

    Who was studied
    76 people who gave stool samples, plus germ-free and antibiotic-treated mice and human fecal microbiota used in lab cultures
    What they received
    a behavioral program to make 41 volunteers chew their food more, plus lab experiments with mouse gut microbiomes and human stool bacteria grown outside the body
    Compared with
    people before vs after the chewing intervention, germ-free/antibiotic-treated mice vs normally colonized mice, and different human stool-bacteria donors in lab culture
    Main outcome
    the size of particles found in feces (fecal particle size)
    Quality
    the human findings are mostly correlations from a modest number of people, and the clearest cause-and-effect evidence comes from mouse and lab-dish experiments rather than from people's actual bowel movements.
    Limitations
    human associations are correlational, chewing intervention did not change outcome, mechanistic evidence relies on mouse and ex vivo models rather than direct human testing

    Taken word for word from the abstract

    • n we analyzed FPS by laser diffraction across a total of 76 individuals
    • population we analyzed FPS by laser diffraction across a total of 76 individuals and found FPS to be strongly individualized
    • intervention a behavioral intervention with 41 volunteers designed to increase chewing efficiency did not impact FPS
    • comparator Fecal samples from germ-free and antibiotic-treated mice exhibited increased FPS relative to colonized mice
    • primaryOutcome fecal particle size (FPS) has been known to be shaped by chewing efficiency and diet
    • result Contrary to our initial hypothesis, a behavioral intervention with 41 volunteers designed to increase chewing efficiency did not impact FPS. Dietary patterns could also not be associated with FPS. Instead, we found evidence that human and mouse gut microbiomes shaped FPS.
    • result In humans, markers of longer transit time were correlated with smaller FPS.

    ISME J · PMID 39214074 · Read it on PubMed ↗

  • Ossola et al. 2024

    Does Microbiome Matter in Chronic Intestinal Failure Due to Type 1 Short Bowel Syndrome in Adults?

    Not relevant to normal stool length.Case seriesVery low qualityRelated question

    44 people2024

    higher levels of certain gut bacteria were linked to more stoma output, and fiber intake was linked to hyperphagia

    Who was studied
    adults with short bowel syndrome and chronic intestinal failure (missing part of the small intestine, with a stoma)
    What they received
    gut bacteria (microbiome) composition and diet
    Compared with
    none; patients compared to each other based on clinical features
    Main outcome
    link between gut bacteria/diet and stomal output or hyperphagia (excessive eating)
    Quality
    This is a small observational study of a very specific surgical patient group looking only at correlations, not an experiment, so it can't show cause and effect and doesn't apply to typical stool length questions.
    Limitations
    Observational and correlational design, no control group, specific to patients with surgically short bowels and stomas rather than general bowel function.

    Taken word for word from the abstract

    • population A total of 44 adult type 1 SBS-CIF patients were enrolled.
    • intervention Fecal microbiota was studied by amplicon-based sequencing and volatile organic compounds (VOCs) were assessed by solid-phase microextraction and gas chromatography-mass spectrometry.
    • comparator Patients with increased stomal output showed higher ASVs for Lactobacillus
    • primaryOutcome The aim of this study is to evaluate the microbiome characteristics of adult type 1 SBS-CIF patients according to their clinical features.
    • result Patients with increased stomal output showed higher ASVs for Lactobacillus (Rho = +0.38; p = 0.010), which was confirmed after adjusting for small bowel length (OR = 1.04; 95% CI 1.01-1.07, p = 0.023).
    • n A total of 44 adult type 1 SBS-CIF patients were enrolled.

    Nutrients · PMID 39064725 · Read it on PubMed ↗

  • Lin et al. 2024

    Effects of Lactocaseibacillus paracasei subsp. paracasei NTU 101 on gut microbiota: a randomized, double-blind, placebo-controlled clinical study

    Improved bowel regularity, not lengthRandomised trialLow qualityRelated question

    size not given6 weeks

    Probiotic significantly shifted gut microbiota, improved peristalsis, and shortened time between bowel movements compared to placebo

    Who was studied
    Healthy adults
    What they received
    Probiotic supplement (Lactocaseibacillus paracasei NTU 101, Vigiis 101-LAB)
    Compared with
    Placebo
    Main outcome
    Gut microbiota composition, bowel movement frequency and stool quality
    Quality
    Although randomized and placebo-controlled, the abstract does not report how many people were studied or how it measured 'poop length', making it hard to judge reliability.
    Limitations
    Abstract does not report participant number, and the study focuses on gut microbiota, peristalsis, and defecation interval rather than stool length specifically

    Taken word for word from the abstract

    • population gut microbiota modulation effect of an NTU 101 product, Vigiis 101-LAB, on healthy human
    • intervention Vigiis 101-LAB
    • comparator randomized, double-blind, placebo-controlled
    • primaryOutcome gut microbiota modulation effect of an NTU 101 product, Vigiis 101-LAB, on healthy human was investigated
    • result Vigiis 101-LAB significantly modulated human gut microbiota at fourth and sixth weeks of trial (anosim analysis, P = 0.001). It also significantly improved peristalsis (P = 0.003) and shortened defecation interval of subjects.

    J Sci Food Agric · PMID 39051756 · Read it on PubMed ↗

  • Avesani et al. 2024

    Plant-based diet in hyperkalemic chronic kidney disease patients receiving sodium zirconium cyclosilicate: a feasibility clinical trial

    No change in stool pattern.Prospective cohortLow qualityRelated question

    26 people6-wk trial

    stool type and frequency did not change after starting the plant-based diet

    Who was studied
    adults with stage 4-5 chronic kidney disease and high blood potassium taking a potassium-lowering drug
    What they received
    switching to a high-potassium plant-based diet while continuing the potassium binder
    Compared with
    a low-protein, low-potassium diet plus the same potassium binder
    Main outcome
    change in stool type and frequency (Bristol stool scale) after diet change
    Quality
    this was a small, 6-week, non-randomized feasibility trial with only 26 patients and no control group, so it gives weak evidence on stool changes.
    Limitations
    Abstract does not mention randomization, blinding, or a separate control group; stool outcome was secondary to the study's main focus on potassium control.

    Taken word for word from the abstract

    • n 26 hyperkalemic patients with CKD stage 4-5 not on dialysis
    • population hyperkalemic patients with CKD stage 4-5 not on dialysis received a low-protein low-potassium diet plus SZC
    • intervention a PBD with high potassium content delivered as a weekly food basket while continuing SZC
    • comparator a low-protein low-potassium diet plus SZC for 3 wk
    • primaryOutcome Bristol stool scale, Quality of life (QoL), and renal treatment satisfaction were assessed at baseline (week 0), week 3, and week 6
    • result stool type and frequency did not change after starting PBD
    • followUp 6-wk trial

    Am J Clin Nutr · PMID 39032787 · Read it on PubMed ↗

  • Mysonhimer et al. 2024

    Honey Added to Yogurt with Bifidobacterium animalis subsp. lactis DN-173 010/CNCM I-2494 Supports Probiotic Enrichment but Does Not Reduce Intestinal Transit Time in Healthy Adults: A Randomized, Controlled, Crossover Trial

    No change in gut transit time.Randomised trialModerate qualityRelated question

    66 people2 weeks per condition

    Honey yogurt boosted probiotic levels but did not speed up or slow down gut transit time compared to control yogurts

    Who was studied
    healthy adults
    What they received
    yogurt with honey and a probiotic (Bifidobacterium animalis)
    Compared with
    heat-treated yogurt plus sugar (and plain yogurt plus sugar)
    Main outcome
    how fast food moves through the gut (intestinal transit time)
    Quality
    It was a well-controlled crossover trial but used healthy adults, not people with bowel symptoms, and was modest in size.
    Limitations
    Participants were healthy adults, not people with constipation or long stools, and the extension arm was not randomized.

    Taken word for word from the abstract

    • n Sixty-six healthy adults (34 female; 33.6 ± 9.8 y; 24.6 ± 3.0 kg/m2) in a crossover trial were randomly assigned
    • population healthy adults
    • intervention yogurt plus honey and
    • comparator heat-treated yogurt plus sugar
    • primaryOutcome intestinal transit time, probiotic enrichment, digestive health, mood, and cognition
    • result Intestinal transit time, gastrointestinal health, mood, and cognition did not differ between conditions

    J Nutr · PMID 38830472 · Read it on PubMed ↗

  • Tan et al. 2024

    Clinical effects of chemical drugs, fecal microbiota transplantation, probiotics, dietary fiber, and acupuncture in the treatment of chronic functional constipation: a systematic review and network meta-analysis

    Fecal transplant most effective for constipationMeta-analysisLow qualityRelated question

    17,118 people2024

    fecal microbiota transplantation ranked best for symptom improvement, stool form score, and quality of life, while electroacupuncture had the fewest side effects

    Who was studied
    adults with chronic functional constipation
    What they received
    fecal microbiota transplantation, probiotics, dietary fiber, or acupuncture
    Compared with
    chemical drugs (laxatives) and the treatments compared against each other
    Main outcome
    improvement in constipation symptoms, stool form, and quality of life
    Quality
    this is a network meta-analysis combining many different trials and treatments indirectly, which makes the comparisons less certain than a single head-to-head trial.
    Limitations
    abstract does not report study quality, risk of bias, or heterogeneity across the 45 pooled trials

    Taken word for word from the abstract

    • n 17 118 patients with CFC
    • population patients with CFC
    • intervention chemical drugs, fecal microbiota transplantation (FMT), probiotics, dietary fiber, and acupuncture in the treatment of patients with CFC
    • comparator compare the relative efficacy and safety of chemical drugs, fecal microbiota transplantation (FMT), probiotics, dietary fiber, and acupuncture
    • primaryOutcome clinical efficacy, Bristol stool form scale scores, patient assessment of constipation quality of life scores
    • result FMT showed the best utility in terms of clinical efficacy, Bristol stool form scale scores, patient assessment of constipation quality of life scores, and the treatment modality with the lowest ranked incidence of adverse effects was electroacupuncture

    Eur J Gastroenterol Hepatol · PMID 38829940 · Read it on PubMed ↗

  • Jaafar et al. 2024

    Constipation anti-aging effects by dairy-based lactic acid bacteria

    More stool bulk, softer stool, in rats.Animal studyLow qualityRelated question

    size not given2024

    probiotic-treated rats had more and softer stool, higher fecal moisture, and more mucus-producing gut cells than controls

    Who was studied
    aged rats with drug-induced constipation
    What they received
    dairy-derived probiotic bacteria (Lactobacillus fermentum or Lactobacillus plantarum)
    Compared with
    sterile saline control
    Main outcome
    stool bulk, softness, moisture, and gut lining changes
    Quality
    this is an animal study with an induced constipation model, so it may not reflect how human digestion works, and participant numbers aren't given.
    Limitations
    study was done in rats, not humans, and does not address stool length specifically

    Taken word for word from the abstract

    • population Rats were aged via daily subcutaneous injection of D-galactose (600 mg/body weight [kg]), prior to induction of constipation via oral administration of loperamide hydrochloride (5 mg/body weight [kg])
    • intervention LAB strains (L. fermentum USM 4189 or L. plantarum USM 4187) were administered daily via oral gavage (1 × 10 Log CFU/day)
    • comparator the control group received sterile saline
    • primaryOutcome Aged rats as shown with shorter telomere lengths exhibited increased fecal bulk and soften fecal upon administration of LAB strains amid constipation as observed using the Bristol Stool Chart, accompanied by a higher fecal moisture content as compared to the control
    • result increased fecal bulk and soften fecal upon administration of LAB strains amid constipation as observed using the Bristol Stool Chart, accompanied by a higher fecal moisture content as compared to the control (p < 0.05)

    J Anim Sci Technol · PMID 38618031 · Read it on PubMed ↗

  • İnce Palamutoglu et al. 2024

    Probiotics and Prebiotics Affecting Mental and Gut Health

    Yogurt linked to fewer gut symptoms.RetrospectiveLow qualityRelated question

    538 people2024

    People who never ate yogurt had much higher gut symptom scores, and ayran consumption frequency was linked to stool pattern differences, but prebiotic intake did not significantly affect stool scores

    Who was studied
    young adults at a Turkish university, mostly female
    What they received
    frequent consumption of probiotic foods like yogurt and ayran
    Compared with
    infrequent or no consumption of these foods
    Main outcome
    gut symptoms and stool consistency (Gastrointestinal Symptom Rating Scale, Bristol Stool Scale) and mental health scores
    Quality
    This is a survey-based study without controlled intervention, so it can only show associations, not prove cause and effect.
    Limitations
    Observational survey design, self-reported diet and symptoms, mostly female sample, no mention of stool length specifically.

    Taken word for word from the abstract

    • population Data were obtained using an online survey from young adults (n = 538) enrolled at Afyonkarahisar Health Sciences University who agreed to participate in this study in the 2022-2023 academic year.
    • n This study included 538 participants, mostly (85.5%) females.
    • intervention Participants who never consumed yogurt had 7.614 times higher Gastrointestinal Symptom Rating Scale scores than those who consumed yogurt daily (p < 0.01).
    • comparator Participants who never consumed yogurt had 7.614 times higher Gastrointestinal Symptom Rating Scale scores than those who consumed yogurt daily (p < 0.01).
    • primaryOutcome Similarly, the frequency of ayran consumption had a statistically significant effect on Bristol Stool Scale scores (p < 0.05).
    • result However, the frequency of prebiotic consumption did not have a significant effect on Bristol Stool Scale scores (p > 0.05).

    Healthcare (Basel) · PMID 38470623 · Read it on PubMed ↗

  • Fujisue et al. 2024

    Open-Label, Single-Center, Single-Arm Study Evaluating the Efficacy and Safety of Elobixibat for Chronic Constipation in Patients With Heart Failure

    Less straining, lower cholesterol; stool length not studied.Case seriesLow qualityRelated question

    18 people12 weeks

    straining during defecation and cholesterol levels improved significantly, but bowel movement frequency did not significantly increase

    Who was studied
    heart failure patients with chronic constipation
    What they received
    elobixibat 10 mg/day for 12 weeks
    Compared with
    baseline measurements before treatment (no control group)
    Main outcome
    frequency of spontaneous bowel movements, stool consistency, and straining during defecation
    Quality
    This was a small, single-arm study with only 18 patients and no comparison group, so it's hard to know if the treatment itself caused the changes.
    Limitations
    single-center, single-arm design with no control group, small sample size of 18 patients

    Taken word for word from the abstract

    • n administered for 12 weeks to 18 HF patients with chronic constipation
    • population chronic constipation in patients with heart failure (HF)
    • intervention elobixibat (10 mg/day) was administered for 12 weeks
    • comparator single-center, single-arm study
    • primaryOutcome Spontaneous bowel movement (SBM), stool consistency as measured by the Bristol Stool Form Scale, and degree of straining during defecation were recorded
    • result Although there was no significant difference, the frequency of SBM increased by 2.0/week from baseline to Week 12. Both the degree of straining during defecation and low-density lipoprotein cholesterol (LDL-C) levels were significantly decreased at Week 12

    Circ Rep · PMID 38464992 · Read it on PubMed ↗

  • Yamauchi et al. 2023

    The differential effect of two cereal foods on gut environment: a randomized, controlled, double-blind, parallel-group study

    More frequent bowel movements with fiber cereal.Randomised trialLow qualityRelated question

    size not given4 weeks

    Defecation frequency improved, and the two cereal foods affected gut bacteria differently

    Who was studied
    People eating cereal-based foods as part of their diet
    What they received
    Fruit granola or corn flakes eaten daily for 4 weeks
    Compared with
    Fruit granola group compared with corn flakes group
    Main outcome
    Changes in bowel movements, gut bacteria, and gut immune markers
    Quality
    It was a small, double-blind trial but did not report participant numbers and measured bowel frequency and gut bacteria, not stool length.
    Limitations
    Abstract does not state number of participants and focuses on bowel frequency and microbiome, not stool size or length.

    Taken word for word from the abstract

    • population Subjects continuously consume CF or FG for 4 weeks.
    • intervention Cereal-based foods such as fruit granola (FG) and corn flakes (CF)
    • comparator The different cereal-based foods had different effects on gut microbiome.
    • primaryOutcome Stool samples, and questionnaires on defecation were collected before, 2 weeks after, and 4 weeks after intake.
    • result The defecation frequency after cereal based food intake was improved.

    Front Nutr · PMID 38455871 · Read it on PubMed ↗

  • Deutsch et al. 2024

    Relationship Between Colonic Transit Response to Eating With Self-reported Constipation Severity in Constipated Patients According to the Phenotype

    Transit speed tied to severity, varies by type.Prospective cohortLow qualityRelated question

    387 people2024

    Constipation severity was linked to total colon transit time and bloating in IBS-C and FC, but only linked to how the colon responded to eating (left CTRE) in FC and defecation disorder patients, not in IBS-C

    Who was studied
    adult outpatients with chronic constipation (IBS-C, functional constipation, or defecation disorders)
    What they received
    colonic transit response to eating (CTRE), measured by colonic transit time testing
    Compared with
    differences between constipation subtypes (IBS-C, FC, DD)
    Main outcome
    relationship between colonic transit response to eating and self-reported constipation severity
    Quality
    This is an observational study of one group of patients with no comparison to healthy people or treatment, so it can only show associations, not prove what causes long or large stools.
    Limitations
    Abstract does not mention control group, blinding, or adjustment for confounders; study is cross-sectional so cause and effect cannot be determined.

    Taken word for word from the abstract

    • n We included 387 consecutive outpatients complaining of Rome IV chronic idiopathic constipation.
    • population Of the 387 patients included (49.7 ± 16.4 years), 320 (83%) were female, 203 had irritable bowel syndrome with constipation (IBS-C), 184 as functional constipation (FC), and 283 had defecation disorders (DD).
    • intervention total and segmental colonic transit time (CTT), and colonic transit response to eating (CTRE) were performed in all patients
    • comparator 203 had irritable bowel syndrome with constipation (IBS-C), 184 as functional constipation (FC), and 283 had defecation disorders (DD)
    • primaryOutcome The present study aims to evaluate the interplay between self-perceived constipation severity (CS) and colonic response to eating in constipated patients according to the phenotype.
    • result In contrast, in FC, CS was only related to left CTRE (P = 0.006), and in patients with DD, CS was associated with total CTT (P < 0.001) and left CTRE (P = 0.002).
    • result Colonic transit response to eating was not associated to CS in IBS-C patients, but left CTRE was associated with constipation severity in FC and DD patients.

    J Neurogastroenterol Motil · PMID 38173161 · Read it on PubMed ↗

  • Nieh et al. 2023

    Effect of acupressure on alleviating constipation among inpatients with stroke during the acute phase: A randomized controlled trial

    Less constipation after stroke.Randomised trialModerate qualityRelated question

    128 people7 days

    acupressure group had lower constipation scores, less need for laxatives, and less hard stool over time compared to sham group

    Who was studied
    hospital patients with acute stroke experiencing constipation
    What they received
    acupressure at three acupoints twice daily for 7 days
    Compared with
    sham acupressure
    Main outcome
    constipation severity and stool form, measured by Constipation Assessment Scale and Bristol Stool Form Scale
    Quality
    it was a randomized trial with a sham control, but it was small and specific to stroke patients, not general constipation.
    Limitations
    abstract does not mention blinding of outcome assessors or long-term follow-up beyond the 7-day intervention

    Taken word for word from the abstract

    • n In total, 128 inpatients with stroke at the acute phase from neurological departments were randomly assigned
    • population inpatients with stroke at the acute phase from neurological departments
    • intervention acupressure group (ST25, CV12, and CV6) or a sham acupressure group for twice-daily therapy at 4 min per intervention for 7 days
    • comparator sham acupressure group
    • primaryOutcome The Bristol Stool Form Scale and Constipation Assessment Scale (CAS) were assessed at the beginning and completion of the study.
    • result The acupressure group demonstrated gradually lower scores on the CAS over time than the sham acupressure group. Patients who received acupressure had a lower likelihood of requiring defecation medication and were more likely to have normal bowel movements and a decreased risk of their stool appearing as a hard lump than those who received sham acupressure over time.

    Complement Ther Clin Pract · PMID 37793306 · Read it on PubMed ↗

How we searchedThe exact query, the date it ran, and what came back — so you can run it yourself.
Searched
PubMed · ClinicalTrials.gov · Crossref on 2026-10-13
The exact search — paste this into PubMed to repeat it
("Feces"[Mesh] OR stool[tiab] OR stools[tiab]) AND (length[tiab] OR size[tiab] OR caliber[tiab] OR shape[tiab] OR form[tiab] OR "Bristol stool"[tiab]) AND ("Gastrointestinal Transit"[Mesh] OR transit time[tiab] OR "Dietary Fiber"[Mesh] OR fiber intake[tiab] OR defecation[tiab])
PubMed expanded that to: ("Feces"[MeSH Terms] OR "stool"[Title/Abstract] OR "stools"[Title/Abstract]) AND ("length"[Title/Abstract] OR "size"[Title/Abstract] OR "caliber"[Title/Abstract] OR "shape"[Title/Abstract] OR "form"[Title/Abstract] OR "Bristol stool"[Title/Abstract]) AND ("Gastrointestinal Transit"[MeSH Terms] OR "transit time"[Title/Abstract] OR "Dietary Fiber"[MeSH Terms] OR "fiber intake"[Title/Abstract] OR "defecation"[Title/Abstract])
What came back
1060 records found · 199 read · 34 answered the question
Included
  • Human, animal or laboratory studies reporting an outcome relevant to the question
Excluded
  • Records about a different condition or intervention
  • Records reporting no outcome
  • Retracted publications, which are listed but excluded from every count
Limits
  • Details were read from abstracts, not full papers, so anything reported only in a paper's methods section is not captured here.
  • Fields were read from abstracts, not full text, so detail reported only in a paper's methods section is not captured.
  • Evidence strength is adapted from the GRADE framework. It is not a GRADE assessment and was not produced by a GRADE panel.

Automated evidence review — PubMed, ClinicalTrials.gov, Crossref. Search strategy, grading rules and the checks that must pass before anything publishes were written by Allen Kamrava, MD, MBA, FACS, FASCRS, colon & rectal surgery, Beverly Hills. The pages themselves are compiled by software running that method and are not read one by one before publication — saying otherwise would be the one claim here that could not be checked.

How we grade evidence →

  1. 1060records came back from the search
  2. 199were read
  3. 34actually answered the question
Risks and safetyReported side effects and who should be careful.
  • In a small surgical case series, people with an anal narrowing after hemorrhoid surgery had thin stool as a symptom, and most needed a procedure to fix it. This describes people with an already-diagnosed narrowing — it does not show that a long or thin stool in a healthy person signals this problem.
  • Harder stool took more pressure and time to pass in a lab study using artificial stool in healthy volunteers, which may make passing a large or firm stool uncomfortable.
Why people try thisThe reasoning behind the question — not a claim that it works.
  • Noticing a stool that looks unusually long or different than usual naturally makes people wonder if their diet, hydration, or gut is working differently.
  • Online health content and toilet folklore often links stool shape and size to gut health, prompting people to search for reassurance.
  • People who have recently changed their diet, started a supplement, or eaten more fibre may notice a change in stool size and want to know if that's the cause.
  • Concern about serious bowel disease, especially after hearing that 'thin stool can be a warning sign,' drives many people to check whether their own stool is a cause for concern.
Common questionsShort answers, drawn from the same studies.
Why is my poop so long?
No study has tested what makes a single stool long. Diet (especially fibre) and how fast food moves through your gut affect stool softness, weight, and frequency, and probably affect its size too, but no study measured length itself. A long stool on its own, with no other symptoms, is not something research has linked to disease.
What does long, thin poop mean?
Thin stool was described in a small study of people who already had a known narrowing in the bowel after hemorrhoid surgery, and most of them needed a procedure to fix it. No study has tested whether thin stool predicts an undiagnosed narrowing or growth in people without that history, so an occasional thin stool in someone otherwise well hasn't been shown to mean anything concerning.
What happens when you hold your poop too long?
No study in this review tested delaying a bowel movement and its effect on stool shape or length. Related lab work found that harder stool needs more pressure and time to pass, and that slower transit through the colon changes the gut bacteria that help form stool — but 'holding it in' specifically has not been studied.
Does fibre make your poop longer?
Fibre has been shown to make stool softer, heavier, and more frequent, and to speed up gut transit in people with normal bowel function. No study measured stool length as an outcome, so whether fibre makes stool specifically longer hasn't been directly tested.
Should I see a doctor about a long stool?
A single long stool with no other symptoms hasn't been studied as a sign of disease. See a doctor if you notice ongoing changes in bowel habit, persistent thin or pencil-like stool, blood, unexplained weight loss, or pain — these are the situations the available (though indirect) evidence touches on, not stool length by itself.

This is information, not advice

This page summarises published research. It cannot tell you what is happening in your own body, and evidence changes. If something is bleeding, painful, or new, it is worth being looked at — that is a different question from the one on this page, and a better one to bring to a consultation.

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Automated evidence review — PubMed, ClinicalTrials.gov, Crossref. Search strategy, grading rules and the checks that must pass before anything publishes were written by Allen Kamrava, MD, MBA, FACS, FASCRS, colon & rectal surgery, Beverly Hills. The pages themselves are compiled by software running that method and are not read one by one before publication — saying otherwise would be the one claim here that could not be checked.

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