The Bristol Stool Scale or Bristol Stool Chart is a medical aid designed to classify the faeces form into seven groups. It was developed by Heaton and Lewis at the University of Bristol and was first published in the journal Scand J Gastroenterol in 1997. Because the form of the stool depends on the time it spends in the colon, there is a correlation between the colonic transit time and the stool type. The seven types of stool are:
Type 1: Separate hard lumps, like nuts (hard to pass)
Type 2: Sausage-shaped, but lumpy
Type 3: Like a sausage but with cracks on its surface
Type 4: Like a sausage or snake, smooth and soft
Type 5: Soft blobs with clear cut edges (passed easily)
Type 6: Fluffy pieces with ragged edges, a mushy stool
Type 7: Watery, no solid pieces (entirely liquid)
Types 1 and 2 indicate constipation, with 3 and 4 being the "ideal stools" especially the latter, as they are the easiest to pass. 5-7 being further tending towards diarrhea.
The average passage time of undigested food residues through the human gut is about 50 hours in men and 57 hours in women, but ranges from well under 20 to over 100 hours. It also changes from one day to the next. Most of this time (80 to 90 per cent) is spent in the colon.
The average weight of a stool is about 100 grams (3.5 oz) but, again, this varies a lot. The colour of normal stools is always brown, but, curiously, the nature of the brown pigments is unknown.
The average stool is 75 per cent water, but most of this water is locked up inside bacteria and undigested plant cells. Half to two-thirds of the stool is bacteria ? some living, some dead ? and the rest is mainly undigested residues of plant foods (dietary fibre). Thanks to bacterial activity, there are hundreds of different organic compounds in stools, mainly present in trace amounts.
The average person is said to void wind 12 times in 24 hours. This fact was established in young men (American students) and the situation may be different in older people and in women. There is a great deal of person-to-person variation.
The lack of basic scientific data in this field of human experience is extraordinary. For example, we do not know how many stools float in water and how many sink, nor how long people spend over the act of defecation. It is widely taught that straining (holding the breath and pushing) is a normal and necessary part of defecation. However, recent research has shown that straining is a minority practice and, what?s more, depends on the type, size and consistency of the stool. The most difficult stools to pass are small ones and broad, firm ones. In practice, these are types 1 and 2, or occasionally 3.
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