Mention poo – or bowel motions, number twos or whatever you want to call them – and most people pull a face and change the subject. Yet there’s much you need to know about poo. What goes in must come out, right? So, when was the last time you took a good long look after you went to the toilet?

It’s one thing to talk about the delicious food you’ve been eating, but you probably avoid thinking about what happens to that food as it passes through your body. Yet when it comes out, it may have a message for you.

According to gastroenterologist Dr Derwin Williams, the most important thing poo can let us know about our health is whether we have a bowel tumour. Bowel tumours often bleed so you should always talk to your doctor if you see any blood after you poo.

“What is important is that any blood in your poo should be reported to your doctor,” Williams says.

You might notice blood on the outside of stools, on toilet paper after you wipe or in the bottom of the toilet bowl. As well, certain coloured stools are associated with bleeding. So maroon, dark red, bright red or very black poo (especially if it’s extremely smelly) are worth getting checked out.

While you should never ignore any blood associated with your poo, it’s worth remembering not all bleeding is bowel cancer. Haemorrhoids, anal fissures, bowel polyps, peptic ulcers and a range of other digestive diseases can also cause bleeding.

There’s a chart

But what else can poo tell us about our health? And what is a “normal” poo?

Poo, or faeces or stool as it is referred to in medical circles, text books and polite conversation, is composed of water and solid matter consisting of dead bacteria, indigestible food matter, cholesterol and fats, protein and inorganic substances like iron phosphate. These are all collected along the digestive tract from your mouth to your bottom.

Bowel motions come in a variety of shapes, sizes and consistencies, as described in the Bristol Stool Scale, first published in 1997. The chart aimed to classify human poo into seven categories and was designed as a tool to ascertain a person’s bowel transit time – the time it takes for food to pass through the digestive tract.

These days the chart is more often used to help concerned patients better describe their bowel motions, with numbers 3 or 4 considered ‘the perfect poo’.

Williams says the Bristol Stool Scale is not clinically important and he doesn’t know any colleagues who use it.

“The chart’s really an attempt to work out if someone is constipated [so] every toilet should have a poster,” he says.

“However, if there is any persistent change in the consistency of your poo, it sometimes indicates a problem and should be reported to your doctor.”

Some people tend be obsessed with their poo, and patients have been known to bring photographs and even samples to the doctor’s for an opinion.

But everyone’s poo is different and its appearance changes from day to day. You may see mucus on Monday and have a hard poo on Tuesday. Williams says these variations are nothing to be worried about, unless they are still there a few days later because some factors may be relevant depending on your medical history.

At the far end of the scale (number 7) is diarrhoea. This can be a sign of anything from a tummy bug or food poisoning to a food intolerance, or possibly just a reminder that you had too many alcoholic drinks the night before. As well, some medications can cause diarrhoea. In most cases diarrhoea will clear up after a day or two, but sometimes it will warrant a trip to the doctor.

Colour coding
When we think of poo, we tend to think of a certain shade of brown. But what ends up in the toilet bowel can be anything from brown to green to black. While what you eat can affect the colour of your stools, so can certain health conditions.

Stool gets its brown colour from bile, a digestive fluid produced by the liver. During the digestion process bile mixes with we have eaten, and it changes colour from green to brown as it travels to our colon. Generally, a meal takes three days to pass through the body to reappear in your toilet bowl. In some instances however, this process is sped up (for instance, if you have diarrhoea) and this can lead to green poo.

“A bright green poo indicates a quick transition through the bowel where the bile has had no time to change to brown,” Williams says.

Black poo may contain blood from further up your digestive tract, but it can also mean you are taking iron tablets – or gorging yourself on licorice or blueberries.

While bright red blood on your stools warrant a trip to your doctor as it can mean bleeding in your digestive tract, beetroot can also make your poo look red.

A very pale poo, which can mean a lack of bile, is “pretty rare”, Williams says, although it could mean a bile duct obstruction, which requires medical treatment.

Any changes to your poo’s consistency or colour which last more than a few days should be reported to your doctor, Williams says. But if the only thing that has changed is the colour of your poo – and you have no other symptoms (or any sign of blood) or pre-existing health conditions and these changes don’t last too long – then don’t worry too much.

“The gist of it is that everyone should look at their poo [and] any blood or consistent change should be reported to your GP.

“In our Western culture, we tend to just sit on the loo and flush and we lose the opportunity to take a look. Everyone should look for blood and leave it at that.

Jennifer King has been a digital producer at ABC News Online since 2014 (after a long career as a registered nurse). Follow Jen on Twitter: @JustJenKing