Constipation: Symptoms, Causes and What Helps (UK Guide)

Constipation is pooing fewer than three times a week or less often than is usual for you, with stools that are dry, hard or lumpy, straining or pain when you go, or the feeling that you have not emptied your bowels. That is the NHS definition, and its first half matters: going every other day on a small appetite, comfortably, is not constipation.¹ In 16 trials of 1,251 adults with chronic constipation, two in three responded to a fibre supplement against two in five on placebo, with gel-forming psyllium at 10 to 12 g a day for four weeks or more the best supported; two green kiwis or about 100 g of prunes a day did as well in a head-to-head trial with less bloating.^{2, 3} The causes people miss are a medicine (iron tablets, opioid painkillers such as codeine, some antidepressants), perimenopause, and eating less than before. Blood in your poo, weight you did not try to lose or a sudden change in how you go is a GP appointment, not a remedy.¹

What counts as constipation, and what is normal?

Normal runs from three times a day to three times a week, the range behind the "three poo rule". Constipation is a change from your own normal in the slower direction, plus the stool itself: types 1 and 2 on the Bristol stool chart, the hard lumps readers call rabbit droppings or marbles. You can be constipated and still go every day if what comes out is small, hard and incomplete, and you can feel bunged up with soft stool if the problem is emptying rather than transit. The colon does not store years of old poo, and fibre does not clean it; fibre adds water and bulk so the colon can move what is there.

What causes constipation?

The NHS list covers most people: not enough fibre, not enough fluid, long periods sitting or lying down, ignoring the urge to go, a change of diet or routine, stress, anxiety or depression, and a side effect of medicine. It is more common in pregnancy, after giving birth and over 65, and only rarely caused by a condition such as diverticular disease or bowel cancer.¹

Medicines. Iron tablets upset the gut of around a third of the people who take them; iron supplement side effects explains the alternate-day dosing and gentler forms that help. Opioid painkillers such as codeine slow the whole gut, and bulk fibre is rarely enough against them; some antidepressants, some blood pressure medicines and antacids containing aluminium do the same. See a GP if a medicine is causing constipation, and never stop a prescribed medicine without asking first.¹

Eating less. A small plate makes small stools. On a weight-loss or low-carbohydrate diet, or an appetite-reducing medicine, the fibrous foods go first, fluid falls because much of it comes with meals, and there is less to pass. Going less often then is infrequent, not constipated, unless the stools are also hard and painful.

Perimenopause. Many women find constipation starts or worsens in their forties, often with bloating. Women are constipated more often than men at every age, 10% against 4% in a 9,373-person survey, transit is slower in women, and the hormonal shifts of perimenopause change bowel habit for many; the fixes below are the same, and a change that persists is still a GP conversation.^{4, 5}

Doctors sort chronic constipation into normal transit, slow transit (the colon moves stool too slowly) and evacuation problems (the pelvic floor does not relax, so stool feels stuck however soft it is); the last two are where more fibre can disappoint.

Which foods help constipation, and how much do you need?

In a trial that set the three best-known remedies against each other in adults with chronic constipation, two green kiwis a day, 100 g of prunes a day (eight to twelve) and 12 g of psyllium a day each raised the number of complete bowel movements; kiwi was the best tolerated and psyllium caused the most bloating.³ A pooled analysis of food trials reached the same list, plus rye bread and more fluid.⁶ Prunes at 100 g a day gave 3.5 complete movements a week against 2.8 on 22 g of psyllium in a 40-person crossover,⁷ and 80 g or 120 g a day for four weeks raised daily stool weight by 22 g and 33 g in 120 UK adults, with more wind.⁸ The GB register states it as a fact about the dried fruit: dried plums contribute to normal bowel function at 100 g a day. Wheat bran is the register's transit fibre, "contributes to an acceleration of intestinal transit" at 10 g of wheat bran fibre a day, and each extra gram of cereal fibre added 3.7 g to daily stool weight in pooled trials; it is coarse, needs fluid, and is the fibre NICE tells people with irritable bowel syndrome to steer clear of.⁹ The NHS adds the sorbitol fruits (apples, apricots, grapes and raisins, raspberries, strawberries) and suggests wheat bran, oats or linseed as the additions to try.¹ The sorbitol in those fruits and in prunes is a sugar alcohol that draws water into the bowel.

The smaller questions have smaller answers. A banana is a moderate source, about 2.6 g, neither a remedy nor something to avoid; two wholewheat breakfast biscuits give about 4 g and porridge gives gel-forming oat beta-glucan; wholemeal, seeded or rye bread carries two to three times the fibre of white; eggs have no fibre and do not constipate. Which foods are high in fibre has the grams per portion.

Prune juice is prunes without the fibre: it keeps the sorbitol. A prune juice concentrate is diluted in water, usually around 30 ml in a glass once a day, and supplies potassium, which contributes to normal muscle function where it reaches 15% of the reference intake; like every prune product it carries sorbitol, which some people with irritable bowel syndrome do not tolerate and is counted with sugars on a label.

How does fibre help constipation, and how long does it take?

A fibre does one of three jobs, and the job matters more than the soluble or insoluble on the packet.¹⁰ Gel-formers (psyllium, the beta-glucan in oats) hold water in a soft gel; psyllium is barely fermented, so it reaches the end of the gut still holding that water, which is why it softens hard stools and firms loose ones. Coarse bulkers (wheat bran) add mass and speed transit. Fermentable fibres (inulin, the fructans in onions and wheat, beans) feed bifidobacteria and make gas, and are weak laxatives alone: 12 g a day of chicory inulin raised weekly stools from three to four in a supplier-funded trial of 44 adults, the dose at which the register allows "contributes to normal bowel function by increasing stool frequency".¹¹ Across the 16 supplement trials the benefit was only clear above 10 g a day and after four weeks, psyllium carried most of it, and more wind was the trade-off.² A plain psyllium husk powder at 10 to 12 g a day is the supplement with the evidence. Build any fibre up over two to three weeks, about 5 g every few days, with fluid, because jumping from the roughly 20 g most UK adults eat to 30 g in a week produces the wind and cramps that get fibre blamed for the problem it was meant to help; expect a few days to a few weeks.¹² How much fibre you need a day has the by-age table and what 30 g looks like on a plate.

Bulk fibre comes with a rule. Never take it dry: at least 150 ml of fluid for every 3.5 g and a full glass for a teaspoon of husk, drunk straight away before it thickens, during the day rather than just before bed, and at least an hour either side of other medicines. Do not take it if you have difficulty swallowing, a known narrowing of the gut or a suspected blockage or impaction, and stop and get help for chest pain, vomiting or difficulty swallowing or breathing after a dose.

How much should you drink when constipated?

More than you think, and it may matter more than the fibre: in 9,373 American adults, low fluid intake predicted hard stools and fibre intake did not.⁵ The 2025 British Dietetic Association guideline puts fluid alongside fibre at 1.5 to 2 litres a day, and the NHS's general advice is six to eight glasses, more in hot weather or when you exercise.^{13, 14} Spread it through the day. What you drink before bed does not empty you in the morning; breakfast and a warm drink do, because eating wakes the colon and coffee adds to it in most people. Alcohol dehydrates, and the NHS says to avoid it while constipated.¹

What are the NHS steps, in order?

Food and fluid first, for a few weeks. Then the toilet: go at a regular time, ideally the half hour after breakfast, and do not delay when the urge comes, because the stool dries while it waits. Put your feet on a low stool so your knees are above your hips, lean forward, and breathe out rather than push; that position straightens the last bend of the bowel and is the whole of the "seven-second trick" the videos sell.¹ Only one pressure point, the perineum, has a trial behind it, in 100 adults,¹⁸ and removing stool by hand is something the NHS reserves for a healthcare professional. Walk every day.¹ Then, if diet and routine have not worked, speak to a pharmacist, who can suggest a suitable laxative for a short time; most work within three days, and NICE's order starts with a bulk-forming type, adds an osmotic type if stools stay hard, and a stimulant type if stools are soft but will not shift. In later life, when more medicines constipate, ask the pharmacist or GP about a daily option. Magnesium citrate is the form people take for constipation; which magnesium is best covers what each form does to the bowel.

When is more fibre not the answer?

Fibre helps most people, but a few get worse on more of it. The study often quoted is small: in a Singapore clinic, 41 of 63 people with idiopathic constipation stopped eating fibre and went from one motion every 3.75 days to one a day over six months, none of them bloated, while all six who went back to a high-fibre diet were bloated and stayed at one motion about every seven days.¹⁵ It was uncontrolled and the patients chose their own diets, so it cannot overturn 16 randomised trials, but it names the people in whom piling on bran raises bloating and straining without moving anything: slow transit, where bulk just sits; an evacuation problem, which a GP can refer to physiotherapy; faecal impaction, a mass of hard stool in the rectum that often shows as watery leakage around it and must be cleared by a GP before any fibre is added;¹ a constipating medicine; and a diet so small or so low in carbohydrate that there is little to pass. A GLP-1 weight-loss injection adds a sixth, the slowed stomach, and bulk fibre while you are vomiting, in pain or backed up for days can make it worse; why Mounjaro causes constipation and diarrhoea covers that case. If a fortnight of more fibre with more fluid has made you worse, stop adding it and see your GP.

Piles and fissures: soft, not huge

Many constipation questions are really about piles or an anal fissure, the small tear that gives sharp pain and bright red blood when you go, and both persist because hard stool is forced through. The aim is a stool soft enough to pass without pushing, not a large one, and that changes the fibre: gel-formers (psyllium with its water, oats, kiwi, prunes, the sorbitol fruits), in trials, softened stools, while a heap of coarse bran makes stools bigger, the last thing a fissure wants. The NHS advice for both is the same: plenty of fluid and fibre to keep poo soft, do not ignore the urge, do not push hard or sit longer than you need, a warm shallow bath after you go, keep the area clean and patted dry, and for piles cut down on alcohol and caffeine and avoid painkillers that contain codeine because they constipate.^{16, 17} Blood is a GP conversation the first time; see a GP if piles are getting worse or a fissure has not improved after seven days, and get urgent help for piles with a high temperature, pus or painless bleeding.^{16, 17}

When should you see a GP about constipation?

See a GP if constipation is not getting better with treatment, if you are regularly constipated or bloated, if there is blood in your poo, if you have lost weight without trying, if you are constipated and tired all the time, if you have tummy pain, if a medicine is causing it, or if there has been a sudden change in how you go.¹ NICE sends anyone with bleeding, unexplained weight loss or a persistent change in bowel habit down an urgent referral route; bowel cancer is a rare cause, but that list exists to find it early. Severe, constant tummy pain with a swollen belly, vomiting and no wind or stool passing is the picture of a bowel obstruction and needs 999 or A&E. The food, fluid and routine steps here are safe to try first, including in pregnancy; ask a pharmacist or midwife before any supplement.¹

Frequently asked questions

What is the best late-night snack to help you poo in the morning?

Nothing eaten at night works by morning on its own; the foods with trial evidence take one to three days. Two kiwis or a few prunes in the evening add to the day's fibre; what empties the bowel in the morning is breakfast, a warm drink and ten unhurried minutes with your feet on a stool.³

Is there a homemade laxative that works right away?

No food or drink empties the bowel in 30 minutes. The fastest food routes are prune juice or prunes and kiwis over a day or three; lemon water and "cleanses" have no trials, and olive oil one small dialysis trial.¹⁹ Anything faster is a pharmacist conversation, and home enema recipes are a way to hurt yourself.

Does the "nurse's cocktail" of prune juice, bran and apple sauce work?

No trial has tested the mix. Its parts have some evidence alone: prune juice for its sorbitol, wheat bran at 10 g a day for transit, apples for pectin and sorbitol. As food with plenty of fluid it is harmless for most people, but not for anyone impacted or backed up for days with pain, and bran suits irritable bowel syndrome badly.⁹

Should I keep eating if I'm constipated?

Yes. Skipping meals removes the two things that move a bowel: the bulk and the reflex that eating triggers. Eat normally with the fibre and fluid above, and seek urgent help only if you are vomiting with a swollen, painful belly.

Sources

1. NHS. Constipation. nhs.uk.
2. van der Schoot A, et al. The effect of fiber supplementation on chronic constipation in adults: an updated systematic review and meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition, 2022. PubMed 35816465.
3. Chey SW, et al. Exploratory comparative effectiveness trial of green kiwifruit, psyllium, or prunes in US patients with chronic constipation. American Journal of Gastroenterology, 2021. PubMed 34074830.
4. Cummings JH, et al. Fecal weight, colon cancer risk, and dietary intake of nonstarch polysaccharides (dietary fiber). Gastroenterology, 1992. PubMed 1333426.
5. Markland AD, et al. Association of low dietary intake of fiber and liquids with constipation: evidence from the National Health and Nutrition Examination Survey. American Journal of Gastroenterology, 2013. PubMed 23567352.
6. van der Schoot A, et al. Systematic review and meta-analysis: foods, drinks and diets and their effect on chronic constipation in adults. Alimentary Pharmacology and Therapeutics, 2024. PubMed 37905980.
7. Attaluri A, et al. Randomised clinical trial: dried plums (prunes) vs. psyllium for constipation. Alimentary Pharmacology and Therapeutics, 2011. PubMed 21323688.
8. Lever E, et al. The effect of prunes on stool output, gut transit time and gastrointestinal microbiota: a randomised controlled trial. Clinical Nutrition, 2019. PubMed 29398337.
9. de Vries J, et al. Effects of cereal fiber on bowel function: a systematic review of intervention trials. World Journal of Gastroenterology, 2015. PubMed 26269686.
10. McRorie JW, McKeown NM. Understanding the physics of functional fibers in the gastrointestinal tract: an evidence-based approach to resolving enduring misconceptions about insoluble and soluble fiber. Journal of the Academy of Nutrition and Dietetics, 2017. PubMed 27863994.
11. Micka A, et al. Effect of consumption of chicory inulin on bowel function in healthy subjects with constipation: a randomized, double-blind, placebo-controlled trial. International Journal of Food Sciences and Nutrition, 2017. Supplier-funded (full text). PubMed 27492975.
12. NHS. How to get more fibre into your diet. nhs.uk.
13. Dimidi E, et al. British Dietetic Association guidelines for the dietary management of chronic constipation in adults. Journal of Human Nutrition and Dietetics, 2025. PubMed 41081513.
14. NHS. Water, drinks and hydration. nhs.uk.
15. Ho KS, et al. Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms. World Journal of Gastroenterology, 2012. PubMed 22969234.
16. NHS. Piles (haemorrhoids). nhs.uk.
17. NHS. Anal fissure. nhs.uk.
18. Abbott R, et al. Journal of General Internal Medicine, 2015. Randomised trial, 100 adults, 4 weeks. PubMed 25403522.
19. Ramos CI, et al. Journal of Renal Nutrition, 2015. Randomised trial, 50 haemodialysis patients, 4 weeks. PubMed 25238699.