Bile-acid malabsorption

Introduction

Bile acid malabsorption (also known as bile acid diarrhoea) is a disorder in which excess bile acids enter the colon due to impaired reabsorption in the terminal ileum. This stimulates secretion and motility, resulting in chronic watery diarrhoea. It is often under-recognised and misdiagnosed as irritable bowel syndrome with diarrhoea (IBS-D).

Peak Incidence

• The peak age of onset varies by BAM subtype:
  • Type 1 (secondary to ileal disease or resection): typically presents between 20 and 30 years of age.
  • Type 2 (idiopathic/spontaneous): more common in those aged 40 to 60 years.
  • Type 3 (associated with other gastrointestinal diseases): can occur at any age depending on the underlying condition.

Pathophysiology

• Bile acids are synthesised in the liver and secreted into the duodenum to aid fat digestion.
• In the terminal ileum, approximately 95% of bile acids are normally reabsorbed and recycled (enterohepatic circulation).
• If this process is disrupted (e.g. due to ileal resection, inflammation, or idiopathically), excess bile acids spill into the colon.
• Bile acids in the colon stimulate chloride and water secretion and increase motility, resulting in chronic diarrhoea.
• The liver responds by increasing bile acid synthesis, which can be monitored via serum markers.

Symptoms

• Chronic watery diarrhoea (most common presentation).
  • May occur intermittently or postprandially.
  • Severe cases can result in faecal urgency and incontinence.
• Abdominal pain or cramping.
• Excess flatulence and bloating.
• Weight loss, particularly in long-standing or untreated cases.

Signs

• Often non-specific.
• Abdominal distension may be present.
• Clinical examination is usually unremarkable unless there is an underlying disease such as Crohn’s.

Diagnosis

Clinical history is key, especially in patients with:

• Chronic diarrhoea unresponsive to dietary/lifestyle changes.
• Prior terminal ileal resection, radiotherapy, or Crohn’s disease.

Diagnostic tests:

• SeHCAT (75-selenium homocholic acid taurine) retention test – gold standard
  • Measures bile acid retention after oral ingestion of a radiolabelled bile acid.
  • Retention <15% at 7 days indicates bile acid malabsorption.
• Serum 7α-hydroxy-4-cholesten-3-one (C4)
  • Elevated C4 reflects increased hepatic bile acid synthesis.
  • Supportive in centres without access to SeHCAT.
• Faecal bile acid measurement
  • Rarely used due to limited availability and practicality.

Complications

• Reduced quality of life due to unpredictable and socially limiting diarrhoea.
• Weight loss in severe or untreated cases.
• Fat-soluble vitamin deficiencies (A, D, E, K) and malabsorption of other nutrients in prolonged or severe BAM.

Management

1. Lifestyle Modifications

• Low-fat diet (typically <40 g/day) to reduce bile acid secretion and symptom severity.

2. Medical Treatment

• Bile acid sequestrants (first-line therapy):
  • Cholestyramine, colestipol, or colesevelam bind bile acids in the gut, reducing their irritant effect in the colon.
  • Must be taken with meals; may cause bloating, nausea, or interfere with absorption of other medications.

3. Addressing Underlying Causes

• Optimise treatment for Crohn’s disease or other underlying GI disorders.
• Consider referral for small bowel imaging if undiagnosed ileal pathology is suspected.

4. Monitoring & Follow-up

• Review response to treatment and adjust dose as required.

• Monitor weight, vitamin levels, and symptom burden.

• Long-term use of bile acid sequestrants may require supplementation of fat-soluble vitamins.