What your poo says about your gut

Dr Chad OkayFounder, Suna Health

4 min read. Updated .

Your stool is the most useful daily data point about your gut. The 4 things to read: form (Bristol scale 3-4 is healthy), frequency (1-3 a day, or every other day, both fine), colour (medium brown is normal, black, red, pale or grey deserve a doctor), and smell (strong but not foul is normal; sudden change can mean infection or food intolerance). 30 seconds of glancing tells you what an expensive test won't.

Most people don't look. They flush and forget. But your stool is the highest-resolution daily data your gut produces, and it costs nothing to read. Here's what to look for and what each signal means.

Form (Bristol stool chart)

The Bristol stool chart runs from type 1 (separate hard lumps) to type 7 (entirely watery). Most people fluctuate between types 3 and 5 across the week. Healthy zone: type 3 (sausage with cracks) and type 4 (smooth sausage). Type 1-2 is constipation territory. Type 6-7 is diarrhoea.

  • Type 1-2: dehydration, low fibre, low movement, slow transit, sometimes medicines (strong painkillers, GLP-1 injections, iron supplements).
  • Type 3-4: healthy zone.
  • Type 5: soft blob with clear edges. Slightly fast transit but not pathological.
  • Type 6-7: too fast transit. Common after fatty meals, lactose, gluten in the sensitive, an infection passing through, a sensitive-gut pattern, or stress.

Frequency

  • Normal range: 3 times a day to 3 times a week. Wide normal because individuals vary.
  • A change in habit that has not settled: worth seeing a doctor at any age. NICE now recommends a simple stool test (FIT) for an unexplained change in bowel habit with no minimum duration.
  • Less than 3 a week: constipation territory. Look first at fibre, water and movement; medicines and a sluggish thyroid are the ones your doctor can check.
  • More than 3 a day with urgency: a food trigger is the common explanation; the less common causes are your doctor's to check, and worth checking.

Colour

  • Medium brown: normal. Comes from bilirubin (liver bile pigment) modified by gut bacteria.
  • Dark green: usually fast transit (bile didn't have time to change colour) or lots of leafy greens. Mostly fine.
  • Yellow / pale grey: sometimes too much fat passing through. If it is persistent, that is one for your doctor.
  • Black or tarry: blood from the upper GI tract (stomach, small intestine), digested. Iron supplements also do this. Black, tarry stool not explained by iron supplements needs medical help the same day: it can mean bleeding higher up the gut. If you also feel faint or are vomiting blood, call 999 in the UK or 911 in the US.
  • Bright red: blood from the lower GI tract (colon, rectum, haemorrhoids). One-off after a hard stool: probably haemorrhoids. Persistent: see a doctor, especially if it is not clearly from haemorrhoids or you are 50 or over.
  • Bright orange: usually high beta-carotene intake (carrots, sweet potato) or some medications. Rarely concerning.

Smell

  • Strong but not foul: normal. Comes from sulphur compounds bacteria produce.
  • Sudden very foul smell: possibly an infection, poor fat absorption, or a new dietary trigger. If it lasts, mention it to your doctor.
  • Notably worse smell with high-protein meals: more sulphur from amino acid fermentation. Reduce processed meat, increase plant fibre to balance.
  • No smell at all: rare. Possible if very rapid transit (food not fully digested). Or you're paying too much attention.

Other things to read

  • Mucus: small amounts are normal. Large amounts of mucus on stool, or anything that looks like pus: that is one for your doctor.
  • Floating vs sinking: floaters can mean more gas, more fat, or just less dense fibre. Mostly harmless.
  • Visible undigested food: corn, sesame, blueberry skins. Normal, humans don't have enzymes for these. Lots of leafy green or whole nuts: probably fast transit, otherwise fine.
  • Pencil-thin stools persistently: could be a colon narrowing. Worth seeing a doctor if persistent.

What to do with the data

  1. Glance at every bowel movement for 2 weeks. Note Bristol type, colour, frequency.
  2. Identify your baseline. Most healthy adults are type 3-4, once daily, medium brown.
  3. Watch for changes that last 2+ weeks. One-off changes are normal.
  4. If your baseline is type 1-2 with infrequent movements: add fibre (5 g a day for a week, then 5 more), water, and movement. If that isn't enough, a pharmacist can advise on what genuinely helps.
  5. If your baseline is type 6-7: try a 4-week low-FODMAP elimination, or a 2-week dairy-free trial if lactose is the suspect. If morning urgency dominates, tell your doctor that detail: it points somewhere specific.
  6. The serious signals above (black or tarry, persistent bright red, persistent pale grey, weight loss, blood, night-time pain) always deserve a doctor, full stop.

Common questions

Should I be worried about visible food in my stool?
Not usually. Corn, sesame seeds, blueberry skins and tomato skins regularly pass through whole because humans lack enzymes for cellulose. Lots of recognisable food in stool from many meals can mean fast transit (worth checking). Single items occasionally is normal.
How often should I poo?
Anywhere from 3 times a day to 3 times a week is normal range. Pattern stability matters more than the specific number. A sudden change that lasts more than 2 weeks deserves a check, regardless of which direction it changed.
What does a healthy poo look like?
Bristol type 3 or 4: sausage-shaped, soft enough to pass without strain but firm enough to hold its form. Medium brown. Smells but not foul. Once or twice a day is most common.
When should I see a doctor about my stool?
Black or tarry stool not explained by iron supplements. Bright red blood that's persistent. Pale grey or yellow stool persistently. Pencil-thin stool persistently. A new change in bowel habit lasting more than a few weeks (sooner if you are over 50, or with bleeding or weight loss). Weight loss alongside changes. Blood with mucus. Pain that wakes you at night. Family history of bowel cancer plus any change.

Sources

Written by Dr Chad Okay. Contributor: Dr Parisah Hussain, MBChB, BSc (Hons), DRCOG, MRCGP. Last updated 15 September 2026. From Digests.

Digests explains how the body works in general, everyday terms. It is not medical advice. It is not a substitute for someone who can examine you and knows your history, and we do not tell you what dose of any medicine to take.

Where we describe how something is checked or looked after, we follow UK guidance from NICE and the NHS. If you are reading this outside the UK, the same concerns are worth taking to your own doctor, though the tests and routes where you live may differ.

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