Bile acid malabsorption is a problem in your intestines. It causes chronic, watery diarrhea. Bile acids (bile salts) that aren’t absorbed properly in your small intestine pass to your large intestine (colon) where they trigger diarrhea symptoms. You can treat the symptoms with bile acid sequestrants.
Bile acid malabsorption (BAM) is a gastrointestinal disease. It’s a common cause of chronic diarrhea. When bile acids aren’t properly absorbed in your intestines, they build up, upsetting the chemical balance inside. Excess bile acids trigger your colon to secrete extra water, leading to watery stools.
Bile is a substance your liver makes while filtering your blood. Your liver sorts waste products, such as toxins, dead blood cells and excess cholesterol into bile. Bile acids come from synthesizing these products together. The different acids in bile help to stabilize the lipids in the mix and keep them in a liquid form.
Your liver sends bile through your bile ducts to your small intestine to help with digestion. Bile acids in your small intestine help break down fats for absorption. When that work is done, they are supposed to be reabsorbed themselves, returning to your circulation and then your liver to be recycled into bile again.
Malabsorption is any failure of your intestines to absorb all of the chemicals they’re meant to. Malabsorption can be a problem with your intestines themselves, or it may result from a chemical imbalance. For example, you may have too much or too little of a certain chemical for your intestines to absorb.
BAM has been historically underdiagnosed due to a lack of accessible ways to test for it. But studies now show that at least 30% of those diagnosed with functional diarrhea disorders may have BAM. Functional disorders are those that have no apparent cause and are likely to go undetected during a medical examination, such as irritable bowel syndrome (IBS).
BAM is seen in people with conditions such as:
It can also happen in people who receive certain medical treatments including:
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Typical symptoms include:
Some people also have:
Long-term symptoms can include:
About half of people have constant symptoms, and the other half only report occasional symptoms.
The symptoms of bile acid malabsorption — primarily, bile acid diarrhea, or BAD — result from the buildup of bile acids in your colon, where food waste turns to poop. Normally, 95% of the bile acids in your small intestine are reabsorbed in the last segment (the ileum) before passing on to your colon.
When too many are left over, however, they pass into your large intestine with the rest of the waste. Bile acids in your colon irritate the mucous lining, triggering it to secrete extra fluid and speeding up the muscle contractions that move poop along. This causes frequent, urgent diarrhea and cramping.
What causes bile acids to build up in your intestines is another question.
Researchers have classified the possible causes of BAM into four different types. Sometimes they classify BAM as either primary or secondary.
Primary BAM is caused by your liver overproducing bile acids (types 2 and 4.)
Secondary BAM is caused by damage to your small intestine due to disease, surgery or radiation treatment (types 1 and 3.)
Type 1 BAM is caused by a problem with your ileum itself. This is considered true malabsorption, because the problem begins at absorption stage of the bile acid cycle. You may have type 1 BAM if you’ve had the last part of your small intestine surgically removed, altered or bypassed to treat another condition. Certain diseases, such as Crohn’s disease, and treatments such as radiation therapy can also damage the ileum. Significant damage impairs its ability to absorb.
Type 2 BAM has sometimes been called “idiopathic,” which means that it happens spontaneously or for unknown reasons. However, current research suggests that it's a problem with the chemical signaling between your intestines and your liver. This signaling is what normally regulates your bile acid cycle (enterohepatic circulation.) Chemicals in your blood signal when your liver should produce and deliver more bile acids and when it’s time to stop, reabsorb and recycle them. But with type 2 BAM, your liver doesn't get the memo to stop. So, it keeps sending bile acids — too many for your ileum to absorb.
Type 3 BAM is caused by gastrointestinal diseases that can affect your ileum along with other parts of your digestive system. These include celiac disease, chronic pancreatitis and small intestinal bacterial overgrowth (SIBO).
Type 4 BAM is caused by excessive bile acid production as a side effect of taking Metformin.
Severe bile acid malabsorption can eventually lead to bile acid deficiency. If too many bile acids are coming out in your poop instead of recycling back to your liver, your liver will start to run out of bile acids to produce bile with. A lack of bile in your small intestine will affect your digestion and nutrition.
Bile acid deficiency in your small intestine leads to malabsorption of fats and fat-soluble vitamins (A, D, E and K). This can lead to malnutrition and specific problems related to fat-soluble vitamin deficiencies. For example, vitamin D deficiency affects your bones, and vitamin A deficiency affects your vision.
Type 1 BAM specifically may be accompanied by vitamin B12 deficiency. That’s because vitamin B12 is also absorbed in your ileum. In this case, the deficiency isn’t caused by BAM itself but by the condition that causes type 1 BAM — a dysfunctional ileum. Symptoms can include nausea, dizziness and fatigue.
Bile acid deficiency that leads to fat malabsorption may cause weight loss if you have trouble digesting enough calories. In other cases, bile acid malabsorption causes weight gain. This seems to be related to metabolism. BAM, or its causes, may affect the way your body processes and stores calories as fat.
Current guidelines indicate that anyone experiencing chronic diarrhea without a known cause should be screened for bile acid malabsorption. But tests aren’t always available everywhere. Some healthcare providers screen for it simply by prescribing bile acid sequestrants to see if they help.
Tests for bile acid malabsorption include:
The SeHCAT test is considered the preferred test for BAM, but it’s not available in many places, including in the U.S. It’s a type of nuclear medicine imaging test, which means that it introduces a low-dose radioactive tracer material into your body. Computers detect and follow the tracer through your body and take images along the way.
For the SeHCAT test, you swallow a capsule that contains the tracer, along with a synthetic bile acid named SeHCAT. The capsule passes into your small intestine, where it’s absorbed at the same rate as your organic bile acids are. A gamma camera measures the levels of SeHCAT in your system on the first day, and again seven days later. If less than 85% of the SeHCAT remains after seven days, it indicates BAM.
This blood test is considered the next best alternative to the SeHCAT test, and it’s available in the U.S. The test measures levels of an enzyme called C4 in your blood. C4 levels correlate with how many bile acids your liver is producing. Elevated C4 levels are a good indicator of primary BAM (types 2 and 4), which is caused by the overproduction of bile acids.
Elevated C4 levels may also appear in people with secondary BAM (types 1 and 3) if malabsorption triggers their livers to compensate by producing more bile acids. As a result, this test is useful for most people. But it can give false results in people with certain preexisting conditions, such as high cholesterol and metabolic (non-alcoholic) fatty liver disease.
The fecal BA test measures levels of bile acids excreted in your poop. This may be the most direct way of measuring bile acid malabsorption. However, it’s technically challenging and only available in select healthcare centers.
This test also requires special preparation to be effective. You have to eat a specific diet for several days in advance, then collect samples of your poop over a period of 48 hours. Specialists will test the poop for bile acids in a lab. If they determine that your bile acid levels are elevated, it means too many bile acids aren’t being absorbed in your small intestine and are passing into your colon, causing bile acid diarrhea.
The first line of treatment for bile acid malabsorption is medications called bile acid sequestrants or bile acid binders. Cholestyramine and colestipol are most commonly prescribed. Colesevelam is an unlicensed alternative, but some people find it easier to tolerate.
Bile acid sequestrants are positively charged molecules that bind to negatively-charged bile acids in your intestines, preventing them from breaking down small enough to be absorbed. Binding also prevents bile acids from acting on your colon to trigger diarrhea. This helps reduce the symptoms of BAM.
These medicines usually come in a powdered form that you mix with a liquid to drink. Some people find it difficult to swallow due to the taste or texture. Some also experience side effects that they find nearly as uncomfortable as their BAM symptoms. These can include constipation, nausea, bloating and gas.
Bile acid sequestrants can also bind to fat-soluble vitamins in your small intestine. This can prevent your small intestine from absorbing them. Some people who take bile acid sequestrants need to take vitamin supplements. You may need to take them in a form that bypasses your digestion, such as an injection.
Curing bile acid malabsorption depends on the cause. Some conditions are curable and some aren’t. Treating the underlying condition directly may help improve BAM in some cases. In other cases, you may not be able to cure the condition, but chances are good you can still treat the symptoms effectively.
The bile acid cycle is triggered by fat content in your diet. More fat in your small intestine triggers chemical signals that tell your liver to deliver more bile. More bile leads to more bile acids passing into your colon. For this reason, healthcare providers recommend a low-fat diet to help manage BAM.
If you have persistent diarrhea that hasn’t been explained yet, ask a healthcare provider about bile acid malabsorption. This under-recognized and underdiagnosed condition may not be on every healthcare provider’s radar, so you should ask your provider to test you for it or refer you to a specialist who can.
A note from Cleveland Clinic
Many people spend years searching for an accurate diagnosis and effective treatment for their unexplained diarrhea. For those with bile acid malabsorption, there’s hope that those days are coming to an end. More awareness and more accessible ways of screening for the condition will improve diagnosis.
While bile acid malabsorption has many causes, the treatment in all cases is the same. A healthcare provider who suspects BAM may even prescribe treatment as a way of screening for it. Bile acid sequestrants and dietary changes can effectively manage symptoms for most people with BAM.
Last reviewed by a Cleveland Clinic medical professional on 10/19/2022.
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