Bile acid diarrhea, also known as bile acid malabsorption (BAM), is a gastrointestinal condition that leads to chronic, watery diarrhea. It arises when an excessive amount of bile acids enter the large intestine. This overflow disrupts the normal balance within the colon, causing it to secrete more water than usual, resulting in watery and frequent stools. While often disruptive to daily life, the condition is manageable.
The Role of Bile Acids in Digestion
Bile acids are a component of bile, a digestive fluid produced by the liver and stored in the gallbladder. When you consume food, particularly fats, the gallbladder releases bile into the small intestine. Here, bile acids act like a detergent, breaking down large fat globules into smaller particles that can be more easily absorbed. This process is necessary for absorbing fat-soluble vitamins from your diet.
After their digestive task is complete, around 95% of these bile acids are reabsorbed into the bloodstream in the final section of the small intestine, the ileum. This recycling system, known as the enterohepatic circulation, allows the liver to reuse these acids. This loop ensures the right amount of bile acid is available for digestion.
Causes of Bile Acid Malabsorption
The breakdown in the bile acid recycling process can happen for several reasons, categorized into different types of BAM. Type 1 BAM occurs as a consequence of diseases or surgical interventions that affect the ileum, the primary site of bile acid reabsorption. Conditions like Crohn’s disease can damage the ileum and impair its ability to reclaim bile acids, and the surgical removal of this part of the small intestine (ileal resection) also compromises this function.
Type 2 BAM, often called primary BAM, is diagnosed when there is no clear underlying intestinal disease. In these cases, the issue may stem from the liver overproducing bile acids, which overwhelms the ileum’s capacity for reabsorption. This overproduction is thought to be caused by a disruption in the negative feedback signals that normally tell the liver to slow down.
A third category, Type 3 BAM, develops from other medical conditions not directly located in the ileum. This can include diseases of the pancreas, celiac disease, or having had the gallbladder removed (cholecystectomy). After a cholecystectomy, bile may be released into the intestine more continuously, which can contribute to an excess of bile acids reaching the colon.
Associated Symptoms and Diagnosis
The most prominent symptom of bile acid diarrhea is chronic, watery stools that can be urgent and difficult to control. People with this condition often experience frequent bowel movements, abdominal cramping, and bloating. In some instances, the stool may have a distinctive yellow or green hue due to the presence of bile.
Diagnosing bile acid diarrhea can be challenging because its symptoms overlap considerably with Irritable Bowel Syndrome with Diarrhea (IBS-D). It is estimated that up to a third of individuals diagnosed with IBS-D may have underlying BAM. A common diagnostic approach is a therapeutic trial of a medication known as a bile acid sequestrant. If the patient’s diarrhea improves significantly while taking the medication, it strongly suggests BAM is the cause.
More definitive diagnostic tests exist but are not always widely available. The 75SeHCAT scan is a specialized imaging test that measures how well the body retains bile acids over several days. Blood tests that measure specific markers related to bile acid production can also provide diagnostic clues, and stool tests can directly measure the amount of bile acid in a sample.
Management and Treatment Strategies
The primary medical treatment for bile acid diarrhea involves medications called bile acid sequestrants. This class of drugs includes cholestyramine, colestipol, and colesevelam. These medications work directly within the intestines by binding to the excess bile acids. This action prevents the bile acids from irritating the colon, thereby firming up the stool and reducing frequency and urgency.
Alongside medical treatment, dietary modifications can play a substantial role in managing symptoms. Following a low-fat diet is often recommended because dietary fat stimulates the release of bile. By reducing fat intake, the body produces and releases less bile acid, which in turn reduces the amount that can spill over into the colon. Avoiding specific trigger foods, which can vary from person to person but may include spicy or processed items, can also be beneficial.