What Is Bile Acid Malabsorption?
Bile acid malabsorption (BAM) occurs when bile acids — produced by the liver and stored in the gallbladder to help digest dietary fats — are not properly reabsorbed in the terminal ileum. Instead of being recycled back to the liver (a process called enterohepatic circulation), excess bile acids pass into the colon, where they stimulate water secretion and accelerate motility. The result is chronic watery diarrhoea that can be severe, urgent, and debilitating.
Despite being remarkably common, BAM is one of the most underdiagnosed conditions in gastroenterology. Studies suggest that up to 30% of patients diagnosed with IBS-D (diarrhoea-predominant irritable bowel syndrome) actually have bile acid malabsorption as the primary cause of their symptoms.
Types of Bile Acid Malabsorption
Type 1: Ileal Disease
When the terminal ileum is damaged or surgically removed, it cannot reabsorb bile acids effectively. This occurs in Crohn's disease affecting the ileum, after ileal resection surgery, or following radiation therapy to the pelvis. This is the most well-recognised type.
Type 2: Primary (Idiopathic)
In primary BAM, the ileum is structurally normal, but bile acid production is excessive. This is due to a deficiency of FGF19 (fibroblast growth factor 19), a hormone produced by ileal cells that normally signals the liver to reduce bile acid synthesis. When FGF19 is low, the liver overproduces bile acids, overwhelming the ileum's reabsorptive capacity. This is the most common type and the one most frequently misdiagnosed as IBS-D.
Type 3: Secondary to Other Conditions
BAM can develop secondary to cholecystectomy (gallbladder removal), coeliac disease, small intestinal bacterial overgrowth (SIBO), chronic pancreatitis, or medications including metformin and certain antibiotics.
Symptoms of Bile Acid Malabsorption
BAM symptoms are often indistinguishable from IBS-D, which is why the condition is so frequently missed:
- Chronic watery diarrhoea — typically 3-10 watery stools per day
- Urgency — sudden, intense need to defecate with little warning
- Nocturnal diarrhoea — being woken from sleep by the need to defecate (a red flag that distinguishes BAM from functional IBS)
- Steatorrhoea — pale, greasy, foul-smelling stools indicating fat malabsorption
- Abdominal cramping — particularly in the right lower abdomen
- Faecal incontinence — in severe cases, the urgency and volume overwhelm sphincter control
- Bloating and flatulence — particularly after fatty meals
How to Test for BAM
SeHCAT Scan
The gold standard test is the SeHCAT (selenium homocholic acid taurine) scan, available in the UK, Europe, and some other countries. It involves swallowing a capsule of radioactive synthetic bile acid and measuring retention at 7 days. Retention below 15% indicates BAM; below 5% indicates severe BAM.
Serum C4 and FGF19
In countries where SeHCAT is unavailable (including the United States), serum 7-alpha-hydroxy-4-cholesten-3-one (C4) is used as a surrogate marker. Elevated C4 indicates increased bile acid synthesis. FGF19 levels can also be measured; low FGF19 supports a Type 2 BAM diagnosis.
Therapeutic Trial
Some gastroenterologists use a therapeutic trial of bile acid sequestrants (cholestyramine, colesevelam, colestipol) as a diagnostic tool. If symptoms improve significantly within 1-2 weeks, BAM is the likely diagnosis.
Treatment Options
First-line treatment is bile acid sequestrants, which bind excess bile acids in the intestine and prevent them from reaching the colon. Colesevelam is generally better tolerated than cholestyramine, which has an unpleasant taste and texture. Dietary fat modification — reducing fat intake to decrease bile acid secretion — provides additional symptom relief.
The Gut Microbiome Connection
Bile acids are modified by gut bacteria, and the microbiome plays a role in bile acid malabsorption through several mechanisms. SIBO can impair ileal bile acid reabsorption by damaging the ileal mucosa. Dysbiotic microbiomes produce altered secondary bile acid profiles that affect FXR signalling and FGF19 production. Addressing underlying gut dysbiosis through dietary and microbiome-supportive strategies may improve bile acid homeostasis alongside conventional treatment.
If you have chronic diarrhoea that has been labelled IBS, GutIQ can help evaluate whether your symptom pattern is consistent with bile acid malabsorption, guiding you toward the right diagnostic testing and treatment.