How often should you poo?

Are you a three-times a day kind of person, or is a trip to the lavatory a more rare and special occasion? And crucially, what does your poo frequency reveal about your health? Sit down, relax, and learn about the science of poop. 

How often we go for a number two can vary from person to person. Every time we eat, the large intestine contracts and pushes food along the digestive tract. This automatic "gastro-colic reflex" results in a the release of hormones that create the urge to poo, otherwise known as a "call to stool". Most of us have learnt to suppress this urge, however, meaning that once a day or less has become the new norm.

"We all tend to be too busy to poo," says Martin Veysey, a gastroenterologist and general medicine physician based at Canberra Hospital in Australia.

Conventionally, it has often been claimed that one poo a day is a sign of good gut health. But in the past it wasn't known what constitutes 'normal' when it comes to bowel movements. One study even implied that anything from one bowel action every few weeks or months to 24 poos a day could be regarded as normal.

However, thanks to the pioneering work of scientists like Ken Heaton, a consultant physician at the Bristol Royal Infirmary in the UK, we now known better. In the late 1980s, Keaton and colleagues surveyed residents of East Bristol, asking them the rather impertinent question – how often do you poo? 

The results revealed a huge variety in bowel movements. Although the most common bowel habit was one poo per day, only 40% of men and 33% of women adhered to this practice. Some defecated less than once a week, others three times a day. Overall, the study concluded that "conventionally normal bowel function is enjoyed by less than half the population and that, in this aspect of human physiology, younger women are especially disadvantaged".

People who pooed four soft stools a week were 1.78 times more likely to die within five years than those who pooed normal stools seven times a week

Incidentally this wasn't the only contribution Heaton made to the science of stools. He later helped devise The Bristol Stool Form Scale, which, with its accompanying illustrations, has become a widely used practical guide to help doctors diagnose digestive problems. The scale features handy descriptions of stools varying from "separate hard lumps, like nuts" to "fluffy pieces with ragged edges".

The "goldilocks/ goldiplops" zone

The NHS and other health bodies state that having a bowel movement between three times a day and three times a week is considered normal. But normal and healthy aren't necessarily the same thing. Scientists might have solved the mystery of how often we poo, but it does nothing to answer the question how often should we poo? Increasingly, researchers are finding that a person's bowel movements are a strong indicator of their health.

For example, a 2023 study examined the bowel habits of 14,573 adults in the United States. The most frequent bowel habit was seven times per week (50.7% of people), and the most common poo type was "like a sausage or snake, smooth and soft". Researchers then tracked the participants for over five years to see if there was any relationship between stool frequency and mortality. They found that people who pooed four soft stools a week were 1.78 times more likely to die within five years than those who pooed normal stools seven times a week. Infrequent defecators were also 2.42 and 2.27 more likely to die from cancer and cardiovascular disease, respectively. 

How much is a good amount to poop is also a question occupying Sean Gibbons, a microbiologist at the Institute for Systems Biology in Seattle, the US. In 2024, Gibbons led a study which categorised 1,400 healthy adults into four groups based on their toilet habits; constipated (one-two bowel movements per week); low-normal (three-six bowel movements per week); high-normal (one-three bowel movements per day); and diarrhoea. They then looked to see if there was any association between poo frequency and a person's gut microbiome. 

Gibbons found that frequent pooers who squeezed out one to three stools a day had a higher proportion of 'good' bacteria residing in their guts than those who visited the lavatory less often. On the flip side of the coin, Gibbons found that people who pooed less than three times a week were more likely to have toxins in their blood that have previously been implicated in conditions such as chronic kidney disease and Alzheimer's.

"In the Goldilocks zone of pooing [the high-normal category], we saw a rise in strictly anaerobic microbes that produce chemicals called short chain fatty acids," says Gibbons. One of these short chained fatty acids (SFAs), butyrate, is known to lower inflammation in the body. This is important, because chronic inflammation is now thought to be the driving factor behind conditions such as cardiovascular disease, type 2 diabetes, and even Alzheimer's.

"Having higher levels of butyrate also allows you to control glucose levels in your blood better, so you have better insulin sensitivity," says Gibbons. "Butyrate will also bind to cells in the gut, stimulating them to produce hormones that make you feel full," he says.

Gibbons believes one reason people who were constipated had higher levels of harmful toxins in their blood stream is that when a person has infrequent bowel movements, poo sticks around in their gut for long periods. This causes bacteria in the gut to eat up all of the available fibre, converting it into health-promoting SFAs. The problem, however, is that once all the fibre is gone, the bacteria start fermenting proteins instead – which releases harmful toxins into the bloodstream. These toxins are known to cause damage to organs including the kidneys and heart. One, known as phenylacetylglutamine, is a risk factor for cardiovascular disease, for example. 

"If you have chronically high levels of this metabolite in your circulation, it can promote atherosclerosis, a kind of hardening of the arteries and damage to the cardiovascular system," says Gibbons.

Gibbons says that even though clinical guidance states that between three stools a day to three poos a week is healthy, his study showed that even in the low-normal stool group there was a rise in toxins in the bloodstream. 

"It's hard to say definitively, because we don't have causal data to know whether these people went on to get sick in the future, but it does seem to be the case that, based on what we were looking at, pooping every other day to a couple of times a day is probably a better window to be healthy," says Gibbons.

However, as ever, correlation is not causation. It is possible that people who are already less healthy in other ways might have less frequent bowel movements, although Gibbon's study tried to control for this by only selecting adults who had no reported health concerns.

One measure of the health of your gut is the time it takes for food to travel through your digestive system – known as gut transit time. You can easily test this at home by eating brightly-coloured foods such as sweetcorn, and then timing how long it takes to come out the other end. Generally speaking, the longer a person's gut transit time, the less often they poo, and the more likely they are to suffer constipation.

In 2020, researchers at King's College London gave blue muffins to 863 people to measure their gut transit time. This was part of the Predict1 study – a clinical research project focused on understanding how individual variations in genetics, gut microbiome, and other factors influence how different meals affect blood sugar and fat levels in the body. 

The study revealed that gut transit times varied widely from person to person, ranging from under 12 hours to many days. Remarkably, the microbes found in the guts of people with short transit times – who tended to defecate more often - differed remarkably from those with longer transit times, with a short transit time associated with a healthier gut microbiome.

"What we found was that people who had a longer transit time tended to have more 'bad' gut bacteria, so bacteria that have previously been linked to having worse heart health and metabolic health," says Emily Leeming, a microbiome scientist at King's College London.

This finding was most pronounced for people with a gut transit time of 58 hours or more, who tended to poo less than three times a week.

Like Gibbons, Leeming suspects that in those whose poo spends longer in the gut, microbes aren't getting a fresh meal – so they end up switching from eating fibre and carbohydrates to proteins. This then produces byproducts which are bad for your health.

As well as a healthier gut microbiome, Leeming's study revealed that those with shorter gut transit times benefited from having less visceral fat – a type of fat that lies deep within the belly and surrounds abdominal organs. Visceral fat is dangerous because it can increase your risk of many health conditions, including heart disease, diabetes, and some cancers. Finally, people with short gut transit times also displayed healthier responses to food, known as a 'postprandial response'. This means they had lower levels of sugar and lipids in their blood following a meal, lowering their risk of cardiovascular disease.

The finding fits with what scientists know about constipation, and its links to chronic disease. If someone is chronically constipated, then they may be at higher risk of things like bowel cancer. However, the evidence to support this is mixed – one meta-analysis, a type of study which combines the results from several others which answer the same question, found that bowel cancer was not more prevalent in constipated individuals.

"But we also seeing links with other parts of the body. For example, people with Parkinson's Disease can have constipation up to 20 years before they show any motor symptoms," says Leeming.

Veysey, meanwhile, points to the known link between slow bowel transit and gallstones – hard deposits of bile that form in the gallbladder. "It also raises the risk of developing polyps, pre-cancerous lesions in the bowel, which then can become cancers," he says.

What your poo says about you

Rather than the number of bowel movements a week – which can vary from person to person, Leeming says that the key thing to look out for is any unexplained changes in bowel habits. She also advises that it's a good idea to keep track of your regular pooping habits to get to know what's normal for you. 

"We should all be looking at our poo, because it's basically like a free gut health test," says Leeming. "It's not just how often you go, it's also colour and the shape of your poo as well. What you're really looking for is type 3 to type 4 [on the Bristol Stool Form Scale], which is basically a sausage with cracks in it, or a smooth sausage."

As regards colour, if you see any black or red in your stools, that indicates the presence of blood. Although there could be a harmless explanation for this, it could be a sign of colorectal cancer and so it's important to see a doctor as soon as possible. You should also talk to your doctor if you regularly have diarrhoea or need to go very suddenly, or if you experience a lot of cramps, bloating, and gas after eating.

Finally, if you'd like to become more 'regular', there's three simple things you can do. "In our study, the people in the Goldilocks zone ate more fruits and vegetables, were more hydrated, and were more physically active," says Gibbons.

-BBC