What is Bile Acid Malabsorption?
By Joe Alvarez MSc BSc RD
Background
Bile acid Malabsorption (BAM) is a condition which causes gut symptoms similar to those seen in diarrhoea dominant irritable bowel syndrome (IBS-D). It can vary from mild to severe and can often significantly affect quality of life.
Bile acids are made from cholesterol in the liver, they are then stored in the gall bladder and secreted into the intestines when we eat, where they play a crucial role in the digestion of fats and fat-soluble vitamins by binding fat so it can be absorbed. Usually, 95% of bile acids are reabsorbed, are recycled back to the liver. When absorption is faulty or when bile acid production is increased, high volumes of bile reach the bowel. This causes fluid to move into the colon, which causes symptoms such as; watery, erratic diarrhoea, foul smelling wind, abdominal pain, recurrent episodes of faecal incontinence, nocturnal defaecation (needing to poo at night) and oily stools. This is known as bile acid malabsorption 1,3. It is also called bile acid diarrhoea (BAD) and bile salt malabsorption, and the terms are often used interchangeably4.
The prevalence of BAM is estimated at 1% in the UK 5,6. However studies suggest that of those with IBS-D around a third actually have a diagnosis of BAM. It is widely recognised that BAM is an under-diagnosed condition and is often mis-diagnosed as IBS-D 6,7.
Diagnosis
There are three types of BAM. Type 1 is secondary to Crohn’s disease, ileal resection or radiation damage, type 2 is known as idiopathic BAM, which is the most common presentation. Type 3 is BAM caused by any other condition, this could be pancreatic insufficiency, coeliac disease, post-cholecystectomy and/or bacterial overgrowth.
The main diagnostic tool for BAM is called a SeHCat Scan. After an overnight fast, patient takes a capsule containing radioactive SeHCAT (a synthetic bile acid). Followed by 2 full body camera scans. Diagnosis is classified into mild, moderate or severe and this is dependent on the level of reabsorption of BAs, <5% is considered severe, <10% moderate, <20% mild 2. In cases where access to this scan is limited, patient can be trialled on bile acid sequestrants, and on successful improving symptoms, a diagnosis can be confirmed.
Misdiagnosis of IBS
Many studies suggest that BAM is often not considered as a possible diagnosis. A study in 2009 confirmed that idiopathic BAM is misdiagnosed as diarrhoea predominant irritable bowel syndrome (IBS-D) in 32% of all sufferers6.
Treatment
Medications knows as bile acid sequestrants are considered as the main treatment for BAM. They act by binding bile acids in the intestine, which stops them from being reabsorbed2,3. Cholestyramine, colestipol and colesvelam are the three BA sequestrants available to prescribe in the UK13. Glucagon-like peptide-1 (GLP-1) has been proposed as a potential treatment for some patients with BAM. However, this research is in its infancy and we need to await further trials and studies in order to begin using this as a treatment for patients with BAM16.
What about dietary changes?
In 2017 a study was carried out with data from patients treated at the Royal Marsden hospital in London, who had had a SeHCAT Scan that showed <20% absorption of bile acids. Patients completed a symptom evaluation prior to seeing a dietitian who advised on a low-fat diet (20% of total daily energy from all types of dietary fat). They attended a review at 4-12 weeks after their initial appointment where they provided a food diary and rated their symptoms again. The results showed that out of 114 patients there were statistically significant improvements in abdominal pain and nocturnal defecations and there was a trend of improvements in most other GI symptoms, except abdominal bloating, heartburn and tenesmus17. However, all the patient in the study had been previously treated for cancer and had BAM because of this. In addition, 44% of patients were taking a bile acid sequestrants too. Therefore, we cannot generalise these results to those with other types of BAM (Jackson et al. 2017). Watson et al showed similar results in a similar study of a smaller patient group (n=40) in 2015, also carried out in the same patient group at the Royal Marsden18.
Diet Adequacy
Treatment with bile acid sequestrant can lead to deficiencies in fat soluble vitamins4,19. Therefore, these should be monitored regularly whilst on treatment. A recent evaluation of data from patients who had undergone anti-cancer or haematology treatment found that in those with BAM 76% also had vitamin D deficiency and 50% has Vitamin B12 deficiency. Although, the latter is most likely worsened due to previous gastrectomy, exocrine pancreatic insufficiency, previous resections of ileum or impaired ileal function by previous pelvic radiotherapy20.
People with BA< may also be at risk of malnutrition if they are having severe diarrhoea. This may also affect appetite and intake. Therefore, weight and dietary intake should be monitored and advice given accordingly.
Summary
Bile acid malabsorption is a largely undiagnosed condition in which patients are often mis-diagnosed and treated with IBS-D. Dietitians have a key role to play in recognising patients who may need further investigations to check for BAM. They also have a key role in helping patients to manage the condition, potentially with a low fat diet, ensuring diets are nutritionally adequate and if necessary, that supplementation is provided.
References
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17. Jackson A, Lalji A, Kabir M, et al. The efficacy of a low-fat diet to manage the symptoms of bile acid malabsorption - outcomes in patients previously treated for cancer. Clin Med (Lond). 2017;17(5):412-418. doi:10.7861/clinmedicine.17-5-412
18. Watson L, Lalji A, Bodla S, Muls A, Andreyev HJ, Shaw C. Management of bile acid malabsorption using low-fat dietary interventions: a useful strategy applicable to some patients with diarrhoea-predominant irritable bowel syndrome?. Clin Med (Lond). 2015;15(6):536-540. doi:10.7861/clinmedicine.15-6-536
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