Idiopathic (Primary) Bile Acid Malabsorption and IBS Diarrhea

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In the pursuit of a deeper understanding of the causative factors behind irritable bowel syndrome (IBS), some researchers have turned their attention to a condition known as idiopathic bile acid malabsorption (I-BAM).

What is I-BAM?

Bile acids are substances produced by our livers and stored in our gallbladders. Bile acids digest fats, a process that takes place within our small intestines. If these acids make their way into the large intestine, they stimulate fluid secretion, resulting in loose, watery stools and diarrhea.

This condition is known as bile acid malabsorption (BAM). In the absence of any identifiable gastrointestinal disease or injury, the malabsorption is characterized as Type 2 BAM, otherwise known as idiopathic or primary BAM (I-BAM or P-BAM).

I-BAM is generally thought of as being a rare condition. However, a recent review found that approximately 25 to 30% of patients with IBS-D type symptoms tested positively for I-BAM using a 75SeHCAT scan.

As part of this review, data indicated that patients given targeted medication dosage of bile acid sequestrants relating to the level of malabsorption as measured by the nuclear medicine scan showed symptom improvement. The researchers conclude that an under-diagnosis of I-BAM due to ignorance about prevalence and a lack of access to the scan (it is not available in the U.S.) may be leading to many IBS-D patients not receiving appropriate and effective treatment.

One Possible Theory

Researchers have been trying to further understand what might be behind this bile acid malabsorption problem. One possible culprit is an ileal (small intestine) hormone, FGF19, which is responsible for controlling bile acid production. It may be that low levels of this hormone are resulting in excessive amounts of bile acids causing the spillage into the large intestine.

Research is ongoing to better understand this dysfunction, with the hope that it may lead to medications that directly target the problem.

The Bottom Line

As impressive as the numbers 25 to 30% are, it is important to note that this area of inquiry appears to be driven by one particular group of researchers. And, unfortunately, as the 75SeHCAT scan is not available in the U.S., it is not as if there is a quick blood test to find out if your IBS-D is really I-BAM. However, if you consistently have loose, watery stools as part of your symptom picture, you may want to talk to your doctor to see if you would be a candidate for a trial of the medications that are used to treat BAM (See, "What Is Bile Acid Malabsorption?").


Pattni, S. & Walters, J. "Recent advances in the understanding of bile acid malabsorption" British Medical Bulletin 2009 92:79-93.

Walters, J. "Defining primary bile acid diarrhea: making the diagnosis and recognizing the disorder" Expert Reviews 2010 4:561-567.

Wedlake, L., "Systematic review: the prevalence of idiopathic bile acid malabsorption as diagnosed by SeHCAT scanning in patients with diarrhoea-predominant irritable bowel syndrome" Alimentary Pharmacology and Therapeutics 2009 30:707-717.

Walters, J. "Defining primary bile acid diarrhea: making the diagnosis and recognizing the disorder" Expert Reviews 2010 4:561-567.

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