What Bristol stool type is IBS-D?

IBS-D (diarrhoea-predominant IBS) is defined under Rome IV criteria as more than 25% of bowel movements being Bristol types 6 or 7, with fewer than 25% being types 1 or 2. Rome IV counts those percentages across days with at least one abnormal bowel movement, not across every stool in the log. Types 6 (mushy, ragged) and 7 (watery, liquid) indicate fast colonic transit and represent diarrhoea on the Bristol scale.

What Bristol stool type is IBS-C?

IBS-C (constipation-predominant IBS) is defined as more than 25% of bowel movements being Bristol types 1 or 2, with fewer than 25% being types 6 or 7. As with the other subtypes, Rome IV works the percentages out over days with at least one abnormal bowel movement rather than over the whole log. Types 1 (separate hard lumps) and 2 (lumpy sausage) indicate slow transit and constipation.

Do you count every bowel movement when working out your IBS subtype?

No. Rome IV (2016) calculates the 25% thresholds using bowel movements on days with at least one abnormal bowel movement, meaning a stool of Bristol type 1-2 or 6-7. Normal stools passed on those same days are included; days that were entirely normal are excluded. This is the change from Rome III, which used every bowel movement in the period, and it was made because the older denominator left too many patients unclassified as IBS-U.

This is an educational resource, not a diagnostic tool. For persistent changes in bowel habit, any blood in your stool, unintentional weight loss, or new symptoms that worry you, book an appointment with your GP. In an emergency call 999. This site is not affiliated with the NHS, Bristol Royal Infirmary, Cleveland Clinic, or any medical institution.

Bristol Stool Chart for IBS: Understanding IBS-C, IBS-D, and IBS-M

Q: Can your IBS subtype change over time?

Yes. IBS subtypes are not fixed. Rome IV treats the subtype as something that can be re-categorised as your bowel habit changes, and follow-up studies find a substantial proportion of patients move between IBS-C, IBS-D, and IBS-M over weeks to months. One trial recorded around a third of patients shifting subtype between two assessments. This is why logging stool form over at least two weeks gives a more reliable picture than a single appointment.

Q: Does IBS overlap with other digestive conditions?

Often. IBS frequently overlaps with other functional gastrointestinal disorders, especially functional dyspepsia (recurrent upper-abdominal pain or fullness). In studies using Rome IV criteria, around half of people who meet the criteria for IBS also meet the criteria for functional dyspepsia. Overlap tends to mean more severe symptoms and is worth flagging to your GP, as it can change which treatments help.

Rome IV IBS subtypes mapped to Bristol types - Updated September 2026

Quick answer

Under the Rome IV criteria, your IBS subtype depends on how often your stools are abnormal in form on the Bristol Stool Chart. Types 3-5 are the normal range; the 25% thresholds apply to the hard (types 1-2) and loose (types 6-7) ends.

IBS-C (constipation): more than 25% of bowel movements are types 1-2, fewer than 25% are types 6-7.
IBS-D (diarrhoea): more than 25% are types 6-7, fewer than 25% are types 1-2.
IBS-M (mixed): more than 25% are types 1-2 and more than 25% are types 6-7.
IBS-U (unsubtyped): neither end exceeds 25%.

The denominator is the catch. Rome IV counts those percentages across the bowel movements you had on days with at least one abnormal stool, not across every stool in the period. Rome III used the whole log; Rome IV narrowed it because too many patients were coming out unclassified.

What Is IBS? The Rome IV Definition

Irritable Bowel Syndrome (IBS) is a functional bowel disorder characterised by recurrent abdominal pain associated with defecation or a change in bowel frequency or form. Under the Rome IV diagnostic criteria (2016), IBS is diagnosed when recurrent abdominal pain occurs at least one day per week in the last three months, with two or more of the following: pain related to defecation; change in frequency of stool; change in form (appearance) of stool. Symptoms must have been present for at least six months.

IBS is diagnosed clinically, without specific abnormalities on investigation (no blood, no structural lesion on colonoscopy). It is one of the most common conditions managed in UK primary care. NICE CKS puts prevalence in the general population at 5-20%, and notes this may be an underestimate because many people with symptoms never seek medical advice. The spread is largely down to which criteria a study uses: the Rome Foundation global survey of 73,076 people found 4.1% under Rome IV against 10.1% under the looser Rome III. The Bristol Stool Chart is embedded directly in the Rome IV subtyping system.

IBS Subtypes: How Bristol Types Map to Rome IV

IBS-CConstipation-predominantBristol Types 1-2

Rome IV criteria: More than 25% of stools are Bristol types 1 or 2; fewer than 25% are types 6 or 7.

Treatment focus: Psyllium, osmotic laxatives, linaclotide (NICE-approved), prucalopride

IBS-DDiarrhoea-predominantBristol Types 6-7

Rome IV criteria: More than 25% of stools are Bristol types 6 or 7; fewer than 25% are types 1 or 2.

Treatment focus: Loperamide, antispasmodics, low-FODMAP diet, colestyramine if BAD suspected

IBS-MMixedBristol Types 1-2 and 6-7

Rome IV criteria: More than 25% of stools are types 1 or 2 AND more than 25% are types 6 or 7 (both criteria met).

Treatment focus: Symptom-led: manage whichever pattern predominates at the time

IBS-UUnclassifiedBristol Inconsistent

Rome IV criteria: Meets IBS criteria but stool pattern does not fit C, D, or M.

Treatment focus: Symptom-led management

How to identify your subtype: Log your stool type daily for at least two weeks using our private tracker. Pick out the days on which at least one stool was type 1-2 or 6-7, then, counting only the stools from those days, work out what share were types 1-2 and what share were types 6-7. Apply the 25% thresholds above. Share this data with your GP. Our IBS subtype classifier applies these Rome IV thresholds to your counts automatically and returns IBS-C, IBS-D, IBS-M, or IBS-U.

Your Subtype Can Change, and IBS Often Overlaps with Other Conditions

IBS subtypes are not permanent labels. Rome IV explicitly treats the subtype as something that can be re-categorised as your bowel habit changes, and follow-up studies find a substantial proportion of patients move between IBS-C, IBS-D, and IBS-M over weeks to months. One trial that reassessed patients a short time apart recorded around a third of them shifting subtype between the two assessments, most commonly into the mixed (IBS-M) pattern. This is the practical reason to log your stool form over at least two weeks rather than judging your subtype from a single bad day.

IBS also frequently overlaps with other functional gastrointestinal disorders. The most common overlap is with functional dyspepsia (recurrent upper-abdominal pain, early fullness, or bloating not explained by an ulcer or other structural cause). In studies using Rome IV criteria, around half of people who meet the criteria for IBS also meet the criteria for functional dyspepsia. Overlap tends to track with more severe symptoms and can change which treatments help, so it is worth telling your GP if you have persistent upper-tummy symptoms as well as the bowel pattern.

NHS IBS Treatment Pathway

1. Diet: Low-FODMAP

The low-FODMAP diet is the most evidence-based dietary intervention for IBS. FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols) are short-chain carbohydrates that are poorly absorbed in the small intestine and rapidly fermented by gut bacteria, producing gas and triggering IBS symptoms. The diet involves a 3-6 week elimination phase followed by a structured reintroduction to identify individual triggers.

NICE recommends undertaking low-FODMAP under dietitian supervision where possible. The Monash University Low FODMAP App (developed by the team that created the diet) is available for iOS and Android and provides a comprehensive food guide. Up to 75% of IBS patients report symptom improvement on low-FODMAP.

2. Fibre

For IBS-C, soluble fibre (psyllium husk, oats) generally helps. Insoluble fibre (wheat bran) can worsen bloating and pain in IBS-D. For IBS-D, a low-fibre diet during flares is sometimes helpful, with gradual reintroduction.

3. Probiotics

NICE CG61 does not recommend probiotics as such. What it says (recommendation 1.2.1.6) is that people with IBS who choose to try them should take the product for at least four weeks at the manufacturer's dose while monitoring the effect. It names no strain and no brand. Among the strains with their own published IBS trial data are Bifidobacterium longum subsp. longum 35624 (sold as Alflorex, and long referred to in the literature as B. infantis 35624); Symprove, a multi-strain liquid with UK RCT data for IBS symptom reduction; and Lactobacillus plantarum 299v. See probioticvsprebiotic.com for the full evidence comparison.

4. Antispasmodics

For abdominal cramping and spasm: mebeverine (Colofac), hyoscine butylbromide (Buscopan), and peppermint oil capsules (Colpermin, Mintec) are all available in the UK. Peppermint oil has the most evidence for overall IBS symptom reduction and is effective for both IBS-C and IBS-D variants.

5. Subtype-Specific Prescription Options

IBS-C

Linaclotide (Constella) - NICE-approved, prescribers only
Prucalopride (Resolor) - for chronic constipation not responding to laxatives

IBS-D

Loperamide (Imodium) - OTC, reduces frequency
Colestyramine - if bile acid diarrhoea suspected
Low-dose amitriptyline - tricyclic, second-line; its constipating effect suits IBS-D. Used off-label: CG61 notes tricyclics have no UK marketing authorisation for IBS

6. Psychological Therapies

Cognitive Behavioural Therapy (CBT) and gut-directed hypnotherapy both have strong evidence for IBS, and gut-directed hypnotherapy achieved a 72% response rate in one Australian trial. Be aware of the threshold NICE sets, though: CG61 recommendation 1.2.3.1 says referral for psychological interventions should be considered for people whose IBS has not responded to drug treatment after 12 months and who have a continuing symptom profile, described as refractory IBS. So it is a later step on the NHS pathway rather than an early one. Access also varies by region; ask your GP for a referral or seek an accredited practitioner privately.

Type 1 (IBS-C)Type 2 (IBS-C)Type 6 (IBS-D)Type 7 (IBS-D)Bowel Tracker IBD (not IBS)

Updated September 2026. Sources: Rome IV criteria (2016), including the subtype denominator (bowel movements on days with at least one abnormal bowel movement), subtype re-categorisation, and the documented overlap between IBS and functional dyspepsia (roughly half of IBS patients under Rome IV). Schmulson and Drossman, What Is New in Rome IV, J Neurogastroenterol Motil 2017;23:151-63, for the Rome III to Rome IV denominator change. NICE CG61 IBS guidance (2008, last updated 2017, reviewed April 2025) for recommendations 1.2.1.6 (probiotics) and 1.2.3.1 (psychological interventions in refractory IBS). NICE CKS Irritable bowel syndrome, prevalence, last revised July 2025. Monash University FODMAP research.