What Holding It In Actually Does to Your Gut

Look at what Google suggests when you start typing “why can’t I poop at…” and you get a small, precise map of modern life: at work. At my boyfriend’s house. On vacation. On holiday. At weekends. These are not physiology questions. They are questions about rooms, and privacy, and who might be waiting outside.

The pages that rank for them answer a different question entirely, mostly by repeating the same four unsourced claims about water and hemorrhoids. Almost none of them mentions that somebody ran the experiment. In 1990, twelve men spent a fortnight finding out what happens when you ignore the urge on purpose — and the results are better than any of the advice built on top of them.

The experimentTwo weeks, one variable

The design was straightforward. Twelve healthy male volunteers ate identical food and kept identical activity across two weeks. For one week they went when they felt the urge. For the other they deliberately put it off. The order was randomised, and researchers tracked everything through the gut with radio-opaque markers.

The detail that makes this genuinely interesting is the third row. The slowdown was not spread evenly: time spent in the rectosigmoid — the last stretch before the rectum — went from under nine hours to over thirty-two, a roughly three-and-a-half-fold change. But the right side of the colon, far upstream and nowhere near the action, slowed measurably too. Something about the exit being held shut reached back along the whole system.

Two things to keep in proportion. Twelve healthy young men is a small, narrow sample, it was one week per arm, and the suppression was self-managed and self-reported. And the authors were careful in a way the internet has not been: they concluded that defecation habits may induce changes in colonic function such as those seen in constipation — not that holding it in causes constipation as a disease. It is a demonstration that the effect is real, measurable in seven days, and reversible. It is not a diagnosis.

Where it goesThe most repeated claim, and how solid it actually is

Every article on this subject tells you the same thing: the stool travels back up, the colon draws the water out of it, and it hardens. It is a satisfying story. Here is how much of it is actually established.

The backwards part has real support. Using a 72-sensor probe in nine healthy volunteers, researchers found the rectosigmoid runs a predominantly retrograde pattern — roughly 85 backwards events to 14 forwards ones over two hours — and proposed it as a “rectosigmoid brake” that limits how fast the rectum fills. Their own wording is careful: it “could still act as” such a mechanism. And critically, that study involved no urge suppression at all. It shows a brake exists at rest. It does not show that holding on pushes anything backwards.

The drying part is shakier than you would guess. Slower transit really does associate with firmer stool — in 66 volunteers whose transit was deliberately altered with drugs, stool form tracked transit time better than frequency or output did. But a study that repeatedly measured healthy people’s stools over successive weeks found that while stool size varied tenfold or more, faecal water content was relatively constant. What visibly changes across normal life is form and mass, not the water percentage.

And the honest summary: nobody has measured stool water content before and after voluntary suppression. Klauser measured weight, not consistency. So the standard explanation is plausible, partially supported, and has never actually been watched happening. We are saying so because every other page states it flatly, and it is the least evidenced sentence on the entire subject.

One mechanical link is firmly demonstrated, and it is the one that matters at the end. When researchers had 58 normal subjects and 25 women with severe constipation expel simulated stools, small hard objects required more internal pressure and more time to pass than large soft ones. Firmer and smaller is genuinely harder work, regardless of how it got that way.

It is the roomThe data that just landed

Here is the part that should change how anyone reading this feels about it, and it is three months old.

In May 2026, researchers surveyed 1,000 Dutch schoolchildren about withholding at school. Among 8-to-12-year-olds, 51.2 percent held it in. Among 13-to-16-year-olds, 71.4 percent did. The reasons were not physical in the slightest: hygiene, cited by 84.3 percent, and privacy, cited by 79.3 percent. Four in ten rated their school toilets as insufficiently clean. Half reported abdominal pain.

This is not an isolated finding. A survey of 19,577 children across 252 Danish schools found more than half dissatisfied with their toilets and around a quarter avoiding them, correlating with bowel and bladder symptoms. An older study in Newcastle and Gothenburg found 62 percent of British boys and 35 percent of girls specifically avoided school toilets for this purpose, describing them as unpleasant, dirty and frightening.

These are surveys of children, self-reported, and they show association rather than cause. But the pattern is unmistakable and it is worth naming plainly: the behaviour is driven by the facilities, not by the body. Most people did not develop a personal quirk about unfamiliar bathrooms. They responded, entirely rationally, to a room.

For adults, the striking thing is what is missing. There is no published prevalence study of workplace or public-toilet avoidance in a general adult population — the nearest evidence is a vignette study in university students and a validated scale published in 2016, whose existence tells you how young the field is. There is even a clinical term, parcopresis, for difficulty going when others might be near. Its prevalence in adults has never been measured. If you have quietly assumed you are unusual, the more accurate reading is that nobody has counted.

The long gameWhat is not established, and why we are saying so

The obvious follow-up question is whether doing this for years causes lasting problems. The honest answer is that in adults, this has not been demonstrated.

What exists is suggestive rather than conclusive. A study of 140 women referred for chronic constipation found half had a measurably abnormal perception of the urge, associated with more severe symptoms. But it was cross-sectional, which means it cannot say which came first — whether a blunted urge leads to constipation or constipation changes the urge. And the standard review of reduced rectal sensation states that its cause is unclear, that the evidence supporting abnormal toilet behaviour as a factor is limited, and that it is even uncertain whether the diagnosis reflects true nerve impairment at all.

The claim you will read elsewhere — that the nerves become damaged — has no primary source we could find. The stronger evidence for a withholding-to-constipation pathway comes from children, where it is well documented and written into the international diagnostic criteria. But there the trigger is pain: a painful bowel movement teaches a child to avoid the next one. That is a different mechanism from an adult declining to use a festival toilet, and transplanting one onto the other would be exactly the sort of thing this article exists to avoid.

What helpsThree things, graded

Going when you get the urge. This one has an actual guideline behind it: the American College of Gastroenterology’s 2021 anorectal guideline advises clinicians to tell patients to eat meals of 500 calories or more to trigger the gastrocolonic response, to heed the call to defecate, and to avoid straining. Worth knowing that this sits in the guideline’s narrative discussion as expert advice rather than as a formally graded recommendation — and that at least one review has called bowel-habit modification “probably anecdotal” in terms of hard evidence. It is free, it carries no risk, and it is the single thing Klauser’s experiment actually tested.

Using the morning. Your colon is not equally willing all day. Across 528 hours of recording in 25 adults, waking produced a threefold increase in colonic activity and eating a twofold one — and the powerful contractions that actually move things along occurred a mean of ten times a day, mostly after waking, after meals, or with a bowel movement. Your body also checks the situation constantly on its own: in ambulatory recordings of 15 healthy people, the anal canal sampled what was arriving a median of seven times an hour. Stacking waking and breakfast at home, before the day makes the decision for you, is working with that rather than against it.

A footstool, with more honesty than it usually gets. In a study of 52 people logging 1,119 bowel movements in real time, using one was associated with better emptying and markedly less straining, and 90 percent showed reduced straining across their own diary entries. Three caveats belong with that number. The study was not randomised — everyone did two weeks without the device and then two weeks with it, in that fixed order, unblinded. The one study that measured straining objectively with pressure sensors, in six people, confirmed squatting straightens the anorectal angle (126 degrees versus 100 sitting) but found the reduction in straining did not reach statistical significance. And most tellingly: when Modi’s participants were asked afterwards how it had gone, the reported benefit roughly halved — 90 percent became 65, and 71 percent became 50. The ACG’s position is that a footstool has little if any risk, and that studies are needed.

And the hemorrhoids questionMessier than the internet suggests

Since every page on this topic promises them, it is worth reporting what the evidence actually looks like. Constipation is associated with hemorrhoids — in 2,813 people undergoing screening colonoscopy the odds ratio was 1.43, real but modest. It is associated with anal fissures more strongly: in a population-based cohort of 1,243 cases, chronic constipation appeared in 14.2 percent of people with fissures against 3.6 percent of matched controls.

But the picture resists tidying. When researchers compared people with prolapsing hemorrhoids against severely constipated women, the constipated group — who genuinely did strain and pass hard stools — had none of the prolapsing hemorrhoids the theory predicts, and the authors wrote that this “casts doubt upon the hypothesis that haemorrhoids are caused by constipation.” The same colonoscopy study found sedentary behaviour apparently protective, which is a good sign that these associations are catching something other than simple cause and effect. The ACG does give a strong recommendation to minimise straining — for people who already have symptoms. Nobody has ever tested the full chain that starts with holding it in.

The short versionA real lever, an honest set of limits

One week of deliberately putting it off measurably slowed the gut of twelve healthy men and roughly halved how often they went, and it reversed. Most of the reason people do it is the room rather than the body — the majority of schoolchildren surveyed hold it in, almost entirely over cleanliness and privacy. Whether a lifetime of it causes lasting change has not been shown in adults, and we would rather say that than invent it. The best-evidenced response is unglamorous: go when you can, use the morning while your colon is actually interested, and treat the whole thing as ordinary.

If something has changed and stayed changed, or arrives with pain or bleeding, that is worth a clinician’s time — not because of anything in this article, but because a persistent change in how your body works is always worth a proper look. This article is educational, reports what the cited research measured and where it stops, and is not medical advice.