Bile Acid Malabsorption (BAM), also known as Bile Acid Diarrhea (BAD), is a condition where the body fails to properly absorb bile acids in the small intestine, causing excess bile acids to reach the colon. This excess irritates the colon and leads to chronic diarrhea, bloating, and urgency.

To understand BAM, it is essential to first understand the normal role of bile acids and their remarkable recycling system, known as the enterohepatic circulation.

1. Production and Function: Bile acids are produced by the liver and stored in the gallbladder. When you eat a meal containing fat, the gallbladder releases bile into the first part of the small intestine. Here, bile acids act like a powerful biological detergent, breaking down fats into smaller particles that can be absorbed by the body.
2. The Recycling System: After they have done their job, these valuable bile acids are not meant to be lost. The body has a highly efficient recycling system to reclaim them. As they travel down the small intestine, about 95% of the bile acids are reabsorbed back into the bloodstream in the final section of the small intestine, a specialized area called the terminal ileum. They are then transported back to the liver to be stored and used again.

BAM occurs when this recycling system breaks down. If the terminal ileum is damaged, has been surgically removed, or is otherwise unable to do its job, the bile acids are not reabsorbed. Instead, they “spill over” into the colon.

The colon is not designed to handle large amounts of bile acids; they are highly irritating to its lining. This irritation triggers the colon to secrete large amounts of water and electrolytes, a process known as secretory diarrhea. The result is frequent, urgent, and watery bowel movements. In my experience, BAM is one of the most underdiagnosed causes of chronic diarrhea. Many patients suffer for years without knowing that a simple imbalance in bile recycling is to blame.

Bile acid malabsorption occurs when the enterohepatic circulation, the recycling system that moves bile acids from the intestine back to the liver, is failed. This failure can happen for several reasons, which are used to classify the condition into different types.

• Type 1 BAM (Secondary to Ileal Disease or Resection): This is the classic and most clearly understood cause. It occurs when the terminal ileum, the body’s bile acid recycling center is either surgically removed or is damaged by disease. This includes:
  • Crohn’s Disease: A type of inflammatory bowel disease that commonly affects the terminal ileum.
  • Ileal Resection: Surgical removal of the terminal ileum, often performed as a treatment for Crohn’s disease or certain cancers.
  • Radiation Enteritis: Damage to the small intestine from radiation therapy to the abdomen or pelvis.
• Type 2 BAM (Idiopathic or Primary): In this type, there is no visible disease or surgical history affecting the ileum. For reasons that are still being investigated, the body seems to produce an excess of bile acids, or the signaling system that regulates bile acid production is faulty. This overproduction overwhelms the healthy ileum’s capacity to reabsorb them, leading to spillover into the colon. Many experts believe this is the form of BAM that is most often misdiagnosed as IBS-D (National Institutes of Health [NIH], 2021).
• Type 3 BAM (Secondary to Other Conditions): This category includes cases of BAM associated with various other gastrointestinal or surgical conditions that can disrupt the enterohepatic circulation. These include:
  • Cholecystectomy (Gallbladder Removal): Without the gallbladder to store and regulate the release of bile, bile may flow more continuously into the intestine, potentially overwhelming the reabsorption process.
  • Chronic Pancreatitis.
  • Celiac Disease.
  • Small Intestinal Bacterial Overgrowth (SIBO).

Clinically, I always look for past surgeries or gut inflammation when BAM is suspected. Even gallbladder removal can change bile acid flow enough to trigger symptoms.

You can develop BAM through several pathways, either from damage to the ileum, overproduction of bile acids, or problems with the feedback system that regulates bile recycling.

The primary risk factors for developing BAM are directly related to its causes. You are at a higher risk if you have:

• Undergoing surgery to remove the end of your small intestine (ileal resection).
• A diagnosis of Crohn’s disease, particularly if it affects the ileum.
• Had your gallbladder removed (cholecystectomy).
• Received radiation therapy to your abdomen or pelvis for cancer treatment.
• Been given a diagnosis of Irritable Bowel Syndrome with Diarrhea (IBS-D), as BAM is the true underlying cause in a large subset of these patients.

Patients often say, “I’ve had every test and no one found anything,” and that’s when I start considering BAM, especially if standard IBS treatments haven’t worked.

The symptoms of BAM stem from bile acids irritating the colon, pulling water into the bowel, and causing rapid movement of stool. These symptoms can mimic those of IBS-D or chronic gastrointestinal infections.

The hallmark signs and symptoms include:

• Chronic Watery Diarrhea: This is the defining feature. The diarrhea is often explosive, unpredictable, and associated with a powerful sense of urgency.
• Fecal Incontinence or Urgency: A desperate, sudden need to have a bowel movement.
• Abdominal Cramping and Bloating.
• Excessive Gas (Flatulence).
• Nocturnal Diarrhea: Waking up from sleep with an urgent need to have a bowel movement is a common feature of BAM and is a “red flag” symptom suggesting that the diarrhea is more than just typical IBS.
• Steatorrhea (in severe cases): Greasy, foul-smelling stools due to poor fat absorption. This can also lead to deficiencies in fat-soluble vitamins (A, D, E, K).

Clinically, I often ask patients if they know the exact location of every restroom, they usually do. That urgency is one of the most telling signs of bile acid-related diarrhea.

BAM is frequently underdiagnosed because its symptoms resemble IBS-D. A proper diagnosis requires considering patient history, clinical suspicion, and sometimes specialized testing.

The diagnostic process involves several tools, ranging from advanced nuclear medicine scans to a simple trial of medication.

• SeHCAT Scan (The Gold Standard): The most accurate and definitive test for diagnosing BAM is the 75-selenium homocholic acid taurine (SeHCAT) scan. In this test, the patient swallows a capsule containing a synthetic bile acid that is tagged with a tiny, safe amount of a radiotracer. They receive a scan with a gamma camera to measure the initial amount of radiotracer in their body. They then return seven days later for a second scan. The machine measures how much of the synthetic bile acid the body has retained. A low retention rate (typically less than 15%) confirms a diagnosis of BAM. It is important to note that this gold standard test is only available in a limited number of countries.
• Blood Tests: Newer blood tests that measure markers of bile acid synthesis, such as Fibroblast Growth Factor 19 (FGF19) or 7α-hydroxy-4-cholesten-3-one (C4), can provide clues but are not yet widely used as a primary diagnostic tool.
• Therapeutic Trial (The Most Common Pragmatic Approach): Because the SeHCAT scan is often unavailable, the most common way to diagnose BAM in clinical practice is with a trial of therapy. A doctor who suspects BAM will prescribe a medication called a bile acid sequestrant. If the patient’s chronic diarrhea significantly improves or resolves completely while taking the medication, a diagnosis of BAM is confirmed.

In many cases, I skip the complex tests and start with a therapeutic trial of bile acid binders, if the diarrhea improves significantly, it strongly suggests BAM.

The goal of treatment is to reduce bile acid levels in the colon, relieve symptoms, and restore quality of life.

1. Bile Acid Sequestrants (Binders)

This class of medications is the mainstay of treatment for BAM. These drugs are not absorbed into the bloodstream. Instead, they act like powerful “sponges” that travel through the digestive tract.

• Mechanism of Action: When they reach the colon, they soak up and bind to the excess bile acids, rendering them inert. The medication, along with the bound bile acids, is then passed harmlessly out of the body in the stool. This prevents the bile acids from irritating the colon lining and triggering secretory diarrhea.
• Common Medications:
  • Cholestyramine: Comes as a powder that must be mixed with water or another liquid.
  • Colestipol: Comes as either granules or large tablets.
  • Colesevelam: Comes in tablet form and is often better tolerated than the older medications.
• Considerations: These medications can cause side effects like gas, bloating, and constipation, and the dose often needs to be carefully adjusted. They can also interfere with the absorption of other medications and fat-soluble vitamins, so it is important to time them correctly, usually several hours apart from other drugs.

2. Dietary Modifications

• Low-Fat Diet: A very important part of management is adopting a low-fat diet. Since the gallbladder releases bile in response to eating fat, consuming less fat can reduce the total amount of bile acids secreted into the intestine, which can lessen the severity of the spillover into the colon.

3. Vitamin Supplementation

For patients with severe BAM and fat malabsorption, a doctor will monitor levels of the fat-soluble vitamins (A, D, E, and K) and may prescribe supplements.

I’ve seen dramatic improvements when patients start bile acid binders, many feel relief within days and regain the freedom to leave the house without fear of urgent bathroom trips.

Bile Acid Malabsorption is a common, specific, and treatable physiological cause of chronic watery diarrhea that has for too long been hidden under the umbrella of an IBS-D diagnosis. For the millions of people who have struggled for years with debilitating and unpredictable watery diarrhea, understanding that their symptoms may be caused by a simple problem with bile acid recycling can be a life-changing revelation. The condition can be effectively managed with bile acid sequestrant medications, which act like sponges to stop the colonic irritation. If you have been living with chronic watery diarrhea, especially if it wakes you up at night or if you have a history of gallbladder removal or intestinal disease, it is crucial to speak with your doctor about the possibility of BAM. Patients often feel frustrated after years of misdiagnosis, but once BAM is identified and managed, they’re amazed by how quickly things can turn around.

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). (2021). Bile Acid Diarrhea. Retrieved from https://www.niddk.nih.gov/health-information/digestive-diseases/bile-acid-diarrhea

American College of Gastroenterology (ACG). (2023). Chronic Diarrhea and Bile Acid Malabsorption. Retrieved from https://gi.org/topics/diarrhea-chronic/

Mayo Clinic. (2023). Bile acid malabsorption. https://www.mayoclinic.org