Three conditions hide under chronic non-bloody diarrhoea, and a normal colonoscopy misses all of them.
Bile acid diarrhoea: bile the gut should recycle spills into the colon, which pulls in water and speeds up. Common after gallbladder removal, and a third of cases just appear on their own 1. The 4 a.m. emergency is the tell.
Microscopic colitis: inflammation the camera can't see, only the biopsy can 2. It's the top cause of watery diarrhoea in older women. The trigger is often a drug you've been on for years: a reflux PPI, an SSRI, an NSAID, a statin 3.
Pancreatic insufficiency: fat-digestion failure. Textbook stools are pale, oily and float, but early cases just look soft and frequent with slow weight loss. It shows up in a quarter to forty percent of long-standing type 1 diabetics, who rarely get tested 4.
The reason to push past "just IBS" is how fast the right name pays back. Bile acid sequestrants fix confirmed bile acid diarrhoea in about 70% of people, often within days 5. Six to eight weeks of budesonide puts roughly 80% of microscopic colitis into remission, a number-needed-to-treat of about two 6. Pancreatic enzymes with meals restore fat absorption and the weight you've been losing 7. These are large effects for chronic gut disease.
Bring this list to your doctor. The missing test is what costs years.
Most of the change lands faster than years of illness taught you to expect.
- Days: bile acid sequestrants work almost at once. The 4 a.m. wake stops, coffee stops being a gamble 5.
- Weeks: budesonide drops stool frequency in a couple of weeks, full remission by six to eight 6.
- Months: with enzymes and vitamins, the lost weight and drained energy rebuild 7.
In microscopic colitis, quality of life in remission returns close to the population baseline, not just managed but back to normal 10.
The fine print β when to skip it, and what people get wrong
Why it stayed missed: a "normal" colonoscopy done without biopsies, bile acid testing never considered, or elastase never sent because the stool didn't look oily 4. A "non-response" to enzymes is usually a starter dose taken before the meal instead of during it 7.
Catches before you start: bile acid sequestrants bind other pills (levothyroxine, warfarin, the pill) β separate them by four hours. Budesonide is gentle but still a steroid; keep long courses low. Pancreatic enzymes are pig-derived, so flag it if you avoid pork 7.
- 1Walters et al. (2009). A new mechanism for bile acid diarrhea: defective feedback inhibition of bile acid biosynthesis. Clinical Gastroenterology and Hepatology. link
- 2Pardi DS (2017). Diagnosis and Management of Microscopic Colitis. American Journal of Gastroenterology. link
- 3Miehlke et al. (2021). European guidelines on microscopic colitis: United European Gastroenterology and European Microscopic Colitis Group statements and recommendations. United European Gastroenterology Journal. link
- 4Whitcomb et al. (2023). AGA Clinical Practice Update on the Epidemiology, Evaluation, and Management of Exocrine Pancreatic Insufficiency: Expert Review. Gastroenterology. link
- 5Sadowski et al. (2020). Canadian Association of Gastroenterology Clinical Practice Guideline on the Management of Bile Acid Diarrhea. Clinical Gastroenterology and Hepatology. link
- 6Miehlke et al. (2014). Budesonide is more effective than mesalamine or placebo in short-term treatment of collagenous colitis. Gastroenterology. link
- 7LΓΆhr et al. (2017). United European Gastroenterology evidence-based guidelines for the diagnosis and therapy of chronic pancreatitis (HaPanEU). United European Gastroenterology Journal. link
- 8Singh et al. (2018). Global Prevalence of Celiac Disease: Systematic Review and Meta-analysis. Clinical Gastroenterology and Hepatology. link
- 9Vijayvargiya et al. (2019). Methods for Diagnosis of Bile Acid Malabsorption in Clinical Practice. Clinical Gastroenterology and Hepatology. link
- 10Nyhlin et al. (2014). Long-term prognosis of clinical symptoms and health-related quality of life in microscopic colitis: a case-control study. Alimentary Pharmacology & Therapeutics. link
Related in the handbook (7)
- β Unexplained chronic diarrhoea is often bile acids; a sequestrant fixes it fast.
- β The watery end of the stool scale is chronic diarrhoea; track it to see if treatment is working.
- β Recurrent C. diff is a leading cause of antibiotic-driven chronic diarrhea - when the cycle won't break, a stool transplant usually ends it.
- β A very fast corn test isn't just 'good digestion' β when it's loose and frequent too, it can be the diarrhea that deserves a real workup.
- β Diarrhea that wakes you at night or carries blood is a red flag pointing past ordinary causes.
- β Recurrent C. diff is one cause of diarrhoea that drags on for months β worth ruling in before settling for an IBS label.
- β Bacterial overgrowth is another testable cause hiding under an 'IBS' label β worth ruling in or out during the workup.