The Sensitive Gut

Understanding IBS

Stool Gazing: A Definitive Guide.

Ken Heaton

Dr Kenneth Heaton

In the nineteen sixties before the age of scans and blood tests for everything, medical students were drilled on in the arts of history taking and clinical examination.  Xrays and laboratory investigations were just used for confirmation.  Inspection, palpation, percussion and auscultation were our tests; we used our eyes, our hands, our ears and our noses to make a diagnosis.  And, yes, examination of the stool was considered essential to good clinical practice.



Stool gazing and the humoral theory of illness.

It was Hippocrates who started it.   In the 5th century BCE,  he suggested that health  depended on the balance of the four humours:  blood, phlegm, black bile or yellow bile, a concept that held sway right up until the 18th century AD.   Examination of the stool provided clues as to the state of that equilibrium.  Accordingly, a sanguine stool was moist and soft, a generous bulk, and a rich brown colour and an odour that was not unpleasant, though if a lot of rich food was consumed without sufficient fibre they could be  gummy and foul smelling.  Phlegmatic stools contained a lot of fluid and mucus,  a choleric stool was yellow and irritant and a melancholic (black bile) stool was dark, hard, dry and friable.  The humours were also linked to temperament and emotion.   An excess of choler (anger) was associated with diarrhoea, while melancholia was linked with constipation.  Those of a sanguine temperament were more balanced and equable as long as they regulated their diet.

There is nothing new under the sun.  The idea the nature of the stool could be related to a person’s temperament might be relevant for IBS.  I have often observed that people with IBS-diarrhoea tend to express more anxiety and frustration while those who are constipated can be more resistant and depressed.

Weight and Frequency of Stool.

It is said that the average person living in western cities passes about 200g of stool in a single bowel action every day, but there is enormous variation.   People on vegetarian diet rich in fruit, vegetables and cereal fibre can pass considerably bulkier faeces while the stools of those on a predominantly protein and fat are smaller and harder.  Constipated people may only open their bowels once or twice a week while those with diarrhoea go several times a day.

Consistency and Form

A stool is an extrusion from the rectum of a paste of unabsorbed food residues and bacteria.   This paste is often propelled into the rectum by propagating contractions that are so powerful they can empty the distal section of the colon.  Such ‘mass movements’ occur first thing in the morning when you get up and may also be triggered by eating breakfast (gastro-colonic reflex), but if you have a particularly sensitive bowel they may occur at other times of the day.   It is the arrival of content into the rectum that initiates the urge to defaecate.  So if the conditions are right, you are relaxed and the contents of the colon soft, a gentle push from the abdomen expels it in the shape of a sausage.

The nature of the stool, how thick it is, whether it is broken up into small sausages or extruded as one long coil may depend on a number of factors.  These indlude: the amount of gas present, the sensitivity of the rectum,  the consistency of colonic contents, and whether the timing is convenient.   The colon is still the dark continent of physiology.   The mystery of defaecation is not a topic that has attracted a lot of research despite the considerable distress that it can cause.  Nevertheless current knowledge about colonic function does permit a few speculative insights.

It would seem reasonable to suggest that:

  • Suppressing the urge and holding on while you find a toilet may create a particularly bulky stool.
  • An anxious colon may generate frequent mass movements that continue to dump small amounts of faeces into a sensitive rectum. This may create the urge to pass small packages of stool up until lunch time (see my last post on ‘when you bowels rule your life).
  • The sigmoid colon, the sinuous loop of colon above the rectum, can generate painful contractions in IBS, moulding the paste into hard pellets that are not large enough to generate an urge to defaecate until enough have accumulated They may nevertheless irritate the rectum, causing production of mucus.
  • Thin stools indicate increased tone in the anal sphincter, which suggests increased activity in the sympathetic nervous system.
  • Liquid stools suggest a sensitive colon that fails to salvage the nutrient rich fluid arriving from the small intestine.

The Bristol Stool Scale

In 1997,  Dr Stephen Lewis and Dr Kenneth Heaton, Reader in Medicine at The University of Bristol and guiding light behind the original diagnostic criteria for IBS (The Manning Criteria) published their Bristol Stool Scale, a seven point field guide for stoolgazers.   For the first time, patients had a way of communicating to doctors the nature of their stool without needing to bring a sample.

Bristol Stool Chart


We might question when soft blobs become fluffy pieces, or when nuts become lumps, but The Bristol Scale was never intended as a diagnostic test.  There are, for example, many causes of watery stools.   As Lewis and Heaton concluded from their study1,  which was conducted on normal volunteers given senna to accelerate transit or Imodium to delay it, .  stool form was an index of transit time.  Softer and paler stools contained more water and were indicative of a rapid transit, while if the stool was hard and lumpy, transit time was slower.



Both the yellow to brown colour of the stool and the lemon yellow of urine comes originally from bile pigments.   Bile pigment is derived from the degradation of haemoglobin, released  from disintegrating red blood cells.  The iron is removed and the haem component oxidised to  biliverdin, which has a greenish hue and then rapidly reduced to bilirubin,  which combines with the amino acids, taurine or glycine and becomes a component of bile.  Bile is secreted into the intestine when we digest a meal.  Then when it reaches the colon,  bilirubin is degraded by colonic bacteria to urobilinogen.  Some of this is absorbed and converted in the kidney to urobilin (urochrome), which turns the urine yellow; the remainder stays in the colon and is further reduced by  colonic bacteria to stercobilin, turning the stool brown.  The longer the stool remains in the bowel the more the pigment is reduced and concentrated and the darker it becomes.  Thus rapid transit produces stools that are pale and soft while slow transit produces dark brown stools that are hard and lumpy.

If secretion of bile is blocked by stones or a tumour in the bile duct,  the pigment will not enter the gut and the stool turns a very pale colour like putty, while bilirubin is excreted in the urine turning it as dark as guinness.  So pale stools and dark urine are a clinical sign of obstructive jaundice.

Steatorrhoea is the term used to describe excessive loss of fat in the stool.  This may result from impaired absorption of fat as in coeliac disease or impaired digestion caused by chronic pancreatic disease.  Steatorrhoea stools are characteristically described as pale, bulky and offensive.

Bleeding into the colon caused by colitis, diverticulitis, polyps or cancer may turn the stool red, though if the bleeding occurs higher up in the gut from, for example, a duodenal ulcer, the blood is broken down by bacteria and turns the stool black.  The medical term for this is melaena.  Bleeding from the anus due to haemorrhoids or a fissure may just coat the outside of the stool in a red stripe,  though bleeding due to haemorrhoids is said to ‘splatter round the pan’.

Eating beetroot can also turn the stool red and leach out into the water in the toilet bowl.  The appearance of beetroot in the stool is a good indicator of mouth to colon transit time which is usually between about 24 to 48 hours – one or two days after eating beetroot.  A bright red stool may also be caused by food dyes.  Drinking a lot of Cherry Kool-Aid  is said to make your stools red because it contains Red # 40.

Green stools may be due to chlorophyll and caused by a combination of eating a lot of leafy green vegetables, such as lettuce, cabbage or spinach and a rapid transit that does not allow enough time for these to be degraded.   Iron tablets can also turn the stool greenish.  Finally, drinking large volumes of sports drinks such as Gatorade or Kool Aid (Purplesaurus Rex) is also said to turn the stool bright green.  This is because they contain a food dye (Blue # 1 or 5) that turns green when reduced by colonic bacteria.

The colour blue in the stool is generally produced by food dyes.  Do check if you or your infant has eaten or drank any coloured food recently.   If your infant is passing blue or any other strange colours in their stool, they might have been chewing crayons.

A purple tinge to the stool or purple urine may be diagnostic of acute porphyria.  The doctors attending King George III used to examine the contents of his chamber pot every day to determine whether he was likely to have a relapse.


The presence of excessive amounts of mucus suggests inflammation or irritation of the colon.  This might be because of inflammatory bowel disease (Crohn’s Disease or Colitis),  diverticulitis  or rarely cancer, such as the mucus secreting villous adenoma of the rectum or an intussusception,  where one area of intestine inverts into another and blocks it.    Mucous Colitis is now considered a variant of IBS, where people pass copious amounts of mucus, so much so that mucous casts of the intestine may be passed.  This term has dropped out of mainstream medicine and seems to be a lot less common.  Herbalists recognise that it may be due to emotional stress or depression, but might it be due to the prescription of large amounts of herbal laxatives?

Watery Stools          

Most cases of diarrhoea are related to the failure of intestinal absorption (osmotic diarrhoea),  but some infections or hormone secreting tumours may cause watery diarrhoea even though a person has not been eating any food (secretory diarrhoea)2.  Cholera or dysentery, for example, can result of the passage of odourless ‘rice water’ stools.

Food components

Food is usually so broken down by digestive enzymes and bacteria that little, apart from the thick waxy coats of peas and maize is recognisable in the stool.  If, however, the transit time through the colon is very rapid, other components such as the skins of tomatoes or even green leaves of some vegetables may be seen.    


improved standards of hygeine have meant that worm infestations are less common that they used to be.  Nevertheless, roundworms, threadworms, pinworms, tapeworms and whipworms can still be seen in stool samples as white threads,strings or spheres.

Why do some stools float?

It used to be said that the reason stools is because off the amount of fat in them, but then studies were conducted in which floating stools were subjected to increased hydrostatic pressure in a closed container whereupon they sank, rather like the toy diver containing a bubble of gas in a bottle of carbonated water, indicating it was the gas they contained that caused them to float.  This indicates that floating stools contain unabsorbed carbohydrate that was still being fermented, suggesting that floating stools are either an indicator or malabsorption or of a diet that contains large amounts of fruit and vegetables.


Faeces smell bad because of the breakdown of unabsorbed protein and carbohydrate by colonic bacteria.  The particular odour of faeces depends on the nature of the diet and the composition of colonic bacteria, though not enough is known about the chemical composition of intestinal gases and the bacteria that produce them for a cause to be identified with any certainty.   Skatoles are indoles caused by the bacterial breakdown of tryptophan and have a faeculent odour.  Cadaverine and putrescine are toxic diamines caused by the putrefaction of unabsorbed animal protein.  Sulphur reducing bacteria can metabolise sulphur containing amino acids in meat, some pulses and some sulphur containing preservatives food to produce hydrogen sulphide, the rotten egg odour of chemical laboratories.

In a characteristically sceptical mood, I once suggested that the main benefit of Colpermin, delayed release peppermint oil, was related to the fact when people farted it generated a sweet atmosphere of peppermint.  No wonder British Airways used to offer peppermints to their first class passengers.  But that’s another story!


  1. Lewis SJ, Heaton KW (1997). “Stool form scale as a useful guide to intestinal transit time”. J. Gastroenterol. 32 (9): 920–4.
  2. Read, N. W., Krejs, G. J., Read, M. G., Santa Ana, C. A., Morawski, S. G., & Fordtran, J. S. (1980). Chronic diarrhea of unknown origin.Gastroenterology,78(2), 264-271.

11 comments on “Stool Gazing: A Definitive Guide.

  1. Joan Ransley
    August 10, 2016

    Great article on a subject nobody like to talk about.

    Liked by 1 person

  2. Kate Gwynne
    August 31, 2017

    Very interesting article with a great sense of humour. IBS sufferers have to get used to talking about their bowels but people don’t like it. As a nurse in elderly care, people’s bowel habits become a topic of conversation all the time so I’m used to it.


  3. Lina
    December 2, 2017

    Nice article doc. What would a combination of excessive flatulence, yellow colored stools and bilirubin value of 1.6 for a 53 year old suggest to you ? Thanks in advance.


    • nickwread
      December 7, 2017

      I’m not sure. There could be several explanations. Firstly, a bilirubin level of 1.6 is not very high (normal range 0.2 to 1.2). Pale yellow stools and a highish bilirubin suggests mild obstructive jaundice. If you have no pain, hen this might be due to Gilbert’s Syndrome, an inherited enzymic defect in bilirubin conjugation, which is a harmless condition but may occasionally cause flatulence. Thank you for your comment.


    • Dude
      April 23, 2018

      Fat, flatulent female over forty?

      A mild obstructive jaundice is the first thing someone might think of. If you have right upper quadrant pain or discomfort at times the first thing on anybody’s list for the four F’s is gallstones.


  4. Aleida Olmos
    December 20, 2017

    My 8 year old son has been having type 4 stool with bright red blood on the tip on his stool… Also complains of stomach ache.. Any ideas


    • nickwread
      December 20, 2017

      Thanks for your comment. Blood on the tip of the stool suggests bleeding from the anal canal, possibly a fissure or piles. Softening the stool a bit with fybogel might help, but if it continues, do ask your doctor to take a look with a proctoscope.


  5. Dude
    April 23, 2018

    Very good. As a dude with a hepatobilliary ailment I have become an obsessively paranoid stool watcher. This has helped decrease some paranoia lol.


  6. Joie De Viv
    February 29, 2020

    I’ve been vegan for 2 months now. My stool has been primarily type 5. Is this normal? I pass every day usually in the morning. I noticed that when I haven’t pass for a day, the next day my stool looks more like type 4.


    • nickwread
      February 29, 2020

      This is quite normal on a vegan diet. Fruit and vegetables tend to retain water in the gut resulting in a soft stool, but if you miss a day, then more fluid will be absorbed in the colon resulting in a more formed stool.


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