Constipation: Fibre, Fluids, and When It Needs Investigation
Constipation is common enough to be treated as trivial and unpleasant enough to drive a great deal of self-medication. Most cases respond to a systematic approach, but a few patterns need investigation rather than another laxative.
Defining it properly
Constipation is not simply infrequent stools. Clinically it involves two or more of the following over at least three months:
- Fewer than three spontaneous bowel movements a week
- Hard or lumpy stools
- Straining
- A sense of incomplete evacuation
- A sense of blockage
- Needing manual manoeuvres to pass stool
Normal frequency ranges from three times a day to three times a week. A daily movement is not a requirement of health.
Common causes
Primary or functional, with no structural cause, subdivided into slow transit, normal transit with hard stool, and pelvic floor dyssynergia, where the pelvic floor muscles fail to relax during defecation. The last of these will not respond to laxatives and needs biofeedback physiotherapy.
Secondary causes include:
- Low fibre and low fluid intake, and low overall food volume
- Physical inactivity and immobility
- Ignoring the urge, common with shift work and inaccessible toilets
- Medications: opioids, iron, calcium, aluminium antacids, anticholinergics, some antidepressants, calcium channel blockers, diuretics and some antiepileptics
- Hypothyroidism, diabetes, high calcium, low potassium
- Parkinson’s disease, multiple sclerosis, spinal cord injury
- Pregnancy
- Anal fissure or haemorrhoids, where pain causes avoidance
- Structural narrowing, including tumours and strictures
Fibre, done correctly
Fibre helps, but the type matters and the way it is introduced matters more.
Soluble fibre forms a gel and softens stool. Psyllium husk has the strongest trial evidence. Oats, barley, legumes, apples, guava and flaxseed are food sources.
Insoluble fibre adds bulk and speeds transit. Wheat bran, whole grains, vegetable skins and nuts. It can worsen bloating and pain in irritable bowel syndrome.
Practical rules:
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- Aim for roughly 25 to 30 g of fibre daily, from food where possible
- Increase gradually over two to three weeks, because a sudden jump causes bloating and cramps
- Increase fluid at the same time. Fibre without fluid can worsen the problem and, rarely, cause obstruction
- Psyllium is usually one to two teaspoons in a full glass of water, once or twice daily
- Two kiwifruit daily, or prunes, have specific supporting evidence. Prunes contain sorbitol as well as fibre
Fluid and movement
Extra fluid beyond normal needs helps mainly if you are under-hydrated; drinking litres on top of adequate intake adds little. Warm fluid in the morning can stimulate the gastrocolic reflex. Regular physical activity modestly improves transit, and immobility clearly worsens it.
Toilet habit and position
- Respond to the urge rather than deferring it
- Use the natural post-meal reflex, strongest 20 to 30 minutes after breakfast
- Allow unhurried, private time
- Place your feet on a low stool so the knees sit above the hips, which straightens the anorectal angle
- Lean forward, elbows on knees, and let the abdomen relax outward
- Breathe out gently rather than holding your breath and bearing down hard
Laxative categories
- Bulking agents such as psyllium and ispaghula. First line, safe long term.
- Osmotic agents such as polyethylene glycol and lactulose. PEG has excellent evidence and is safe for prolonged use. Lactulose causes more bloating.
- Stimulants such as bisacodyl and senna. Effective for short courses and for rescue. The old claim that they cause a permanently lazy bowel is not well supported, but continuous daily use should be supervised.
- Stool softeners such as docusate. Weak evidence.
- Suppositories and enemas for faecal loading and for rescue.
- Newer prescription agents such as prucalopride and linaclotide for refractory cases.
Long-term unsupervised use of stimulant laxatives, and any use for weight control, is harmful.
Red flags needing prompt assessment
- New constipation after age 50
- Blood in the stool, or black tarry stool
- Unintentional weight loss
- Anaemia or iron deficiency
- A family history of colorectal cancer or inflammatory bowel disease
- Progressive narrowing of stool calibre
- Alternating constipation and diarrhoea
- Persistent abdominal pain, vomiting or abdominal distension
- Fever
- Failure to improve despite adequate treatment
- Inability to pass stool or gas at all, which is urgent
Investigation may include blood tests for thyroid, calcium and coeliac disease, a colonoscopy, and anorectal physiology testing if a pelvic floor disorder is suspected.
In children and older adults
In children, painful passage leads to withholding, which worsens the loading, and treatment needs adequate disimpaction plus maintenance rather than dietary advice alone. In older adults, faecal impaction can present as overflow diarrhoea or as confusion, and constipation should never be assumed to be simply age.
This is general information. Persistent constipation, and any red flag above, deserves a proper medical assessment rather than escalating self-treatment.