Understanding Bile Acid Diarrhea

Bile acid is a component of bile. Bile is a fluid that aids in digestion.  

Bile acid diarrhea (BAD) is a condition in which bile acids aren't properly processed by the digestive system. This can cause chronic diarrhea.

BAD is also known as bile acid malabsorption (BAM). Malabsorption is an inability of the body to properly absorb certain substances. Some research suggests BAD may not always be due to malabsorption, though.

BAD may not be as rare as it was once thought to be. The condition might be underdiagnosed. This may be preventing people from getting treatment.

Some researchers feel anyone with chronic diarrhea of unknown cause should be evaluated for BAD. This includes people with symptoms of diarrhea-predominant irritable bowel syndrome (IBS-D) or functional diarrhea, which is recurrent diarrhea with no known cause.

This article will discuss bile acid diarrhea, its symptoms, and its causes. It will also discuss diagnosis and treatment of the condition.

Symptoms of Bile Acid Diarrhea

The primary symptom of BAD is chronic bouts of diarrhea. People with BAD may also have some or all of following symptoms:

• Watery diarrhea
• Diarrhea that comes on suddenly
• Diarrhea in the middle of the night
• Soiling accidents
• Bloating

Causes of Bile Acid Diarrhea

Bile acids are produced by your liver and stored in your gallbladder. When you eat foods containing fat, these acids are released into the small intestine. There, they break down fats so your body can absorb them.

Afterward, bile acids are reabsorbed and sent back to the liver for reuse. Typically, very little bile acid ends up in the large intestine.

In people with BAD, large amounts of bile acid get flushed into the large intestine. This causes an increase in fluid in the intestine. The movement of fluid through the intestines speeds up and the result is watery stools.

The following health problems may contribute to the development of BAD:

• Ileal disease, a condition of the small intestine
• Ileal surgery, often done as a treatment for Crohn's disease
• Gallbladder removal, or cholecystectomy
• Small intestinal bacterial overgrowth (SIBO)
• Pancreatic insufficiency, when the pancreas doesn't produce enough digestive enzymes
• Radiation for cancer
• Microscopic colitis, a condition that causes watery diarrhea
• Short bowel syndrome, when a significant part of the small intestine has been removed

Diagnosis of Bile Acid Diarrhea

This condition has three different types. The type depends on the cause:

• Type 1: Results from ileal disease or removal of part of the bowel
• Type 2: Idiopathic or primary, where the cause is unknown
• Type 3: Results from other types of gastrointestinal disease

Testing

Outside the United States, BAD is often diagnosed with a test called a 75-selenium homotaurocholic acid test (SeHCAT). During this test, the patient swallows a capsule containing SeHCAT. SeHCAT is a mildly radioactive synthetic bile acid that shows up on a full-body scan.

Patients undergoing this test receive one scan a few hours after taking the SeHCAT. A second scan is performed a week later.

The test looks at how well the small intestine retains bile acids. If the retention rate is lower than 15%, it indicates BAM.

Unfortunately, this test is not available in the United States. Lack of access to the SeHCAT test may contribute to the underdiagnosis of BAD.

In the United States, stool testing is the most direct way to diagnose BAD. This requires a ​48-hour stool collection to measure bile acids within the colon.

Some doctors use a trial of a medication to treat BAD. If the medication improves symptoms, BAD is diagnosed.

Treatment of Bile Acid Diarrhea

If your BAD is the result of an identifiable disease, your doctor will treat the disease itself. If no underlying cause can be identified, BAD is usually treated with medications called bile acid sequestrants or binders.

Bile acid sequestrants are FDA-approved to treat high blood cholesterol. They are prescribed off-label to treat BAM.

These medications bind to bile acids and reduce their effects on the large intestine. This class of drugs includes:

• Questran (cholestyramine)
• Welchol (colesevelam)
• Colestid (colestipol)

These medications are usually effective in treating the symptoms of BAD. Unfortunately, they are not well-tolerated by many patients. Side effects can include constipation and other digestive symptoms.

Because of this, patients may choose to discontinue treatment, especially if they have not received a diagnosis. If you are prescribed one of these medications, be sure to work with your doctor to find the right dose.

Drugs in this class may affect the absorption of other medications. For that reason, you should take them four to six hours before or after any other medications.

Summary

Bile acid diarrhea is a condition that causes chronic diarrhea. It is caused by excess bile acid in the large intestine. It may be underdiagnosed. BAD may be the actual cause of many cases of chronic diarrhea and IBS-D.

Outside the United States, BAM is diagnosed with a SeHCAT scan. In the United States, doctors rely on stool tests and medication trials to diagnose the condition. BAM can be treated with medication. 

A Word From Verywell

More research is needed, but it's starting to look like BAD may be more common than previously thought. If you have been diagnosed with IBS-D or have undiagnosed chronic diarrhea, talk to your doctor. You may want to find out if this underdiagnosed condition is at the root of your symptoms.