Bile acid diarrhoea is a common cause of chronic watery diarrhoea. Treatment is life-long medication. However, about 50% of people have ongoing, bothersome diarrhoea. Findings from recent research on diet therapies and food intolerances have been used to develop a healthy dietary pattern called The 8x5 Diet. We will test the practicalities of conducting a randomised controlled trial of this dietary intervention.

Bile acid diarrhoea is a lifelong gastrointestinal disorder that causes non-bloody and often urgent, diarrhoea. It is estimated that 1 in 100 adults in the United Kingdom are affected. To manage the diarrhoeal symptoms, daily oral medication is prescribed. About 50% of people are unable to achieve satisfactory symptom control, therefore other therapeutic options are needed. Recent research found a very high prevalence of perceived food intolerances with many people consequently avoiding foods. Systematic review of diet studies in bile acid diarrhoea showed that fat intake reductions and carbohydrate modification may have a beneficial effect on diarrhoea. However, no studies have been conducted as randomised controlled trials, undertaken outside of a hospital recruitment setting, or have assessed nutritional intakes and diet quality. With this paucity of evidence, The 8x5 Diet has been developed.

This study will be conducted virtually to recruit 76 adults from across the United Kingdom who are living with bile acid diarrhoea, have ongoing diarrhoea, and are without any other serious illnesses. Participants will be randomly allocated for 8 weeks to either their usual diet or to trial The 8x5 Diet with detailed advice from a specialist dietitian. The primary objective is to test the feasibility of the trial relating to consent, recruitment, randomisation, and retention. The results will inform the design of a future, definitive, and larger randomised controlled trial.

Inclusion Criteria:

• Age ≥ 18 years, of any ethnic group, living in the United Kingdom and not planning to move home for the next three months
• Self-reported diagnosis of bile acid diarrhoea that was confirmed by 7-day SeHCAT testing
• Self-reported ongoing chronic diarrhoea despite use of appropriate medication
• Able to participate in either diet group with the intention to remain in the group to which they were assigned for the 8 week study period
• Body mass index ≥20 kg m-2
• Able to converse in English (or via their carer, without assistance from an interpreter) using a computer/laptop, smart phone, or tablet
• Able to provide informed written consent
• Able to provide the address of their general practioner so that the research team can inform them of their participation.

Exclusion Criteria:

• Unable to provide self-reported written confirmation that their diagnosis of bile acid diarrhoea was by SeHCAT testing
• Pregnant/breastfeeding/planning a pregnancy in the next six months
• Inflammatory bowel disease, previous or current microscopic colitis, or other serious morbidities such as liver disease, pancreatic disease, AIDS/HIV, radiotherapy for cancer, assessed at screening via patient self-report
• Diarrhoea that is inadequately active: <3 stools per day or <1 watery stool (Bristol Stool Form types 6-7) per day as the mean of one week
• Currently participating in another research study or has taken part in the previous 3 months
• If taking insulin, metformin (other than slow-release), anti-obesity medication, or using commercially available formulated supplements to replace meals in previous three months
• Use of antibiotics in the previous four weeks

Medically necessary dietary exclusions or issues deemed incompatible with the trial:

• Food allergies, other than oral allergy syndrome/pollen-food syndrome
• Exclusion of gluten (i.e. coeliac disease), lactose, biogenic amines, or any other dietary exclusion assessed as unsuitable as screening by the trial team. This includes if the participant knows they would refuse to eat: starchy foods, fruit and vegetables, protein-rich foods, or dairy and alternatives (e.g. following a ketogenic diet)
• An eating disorder or disordered eating which is active or in the last 12 months
• Alcohol or drug abuse, or self-harm, or depression, or suicide ideation in the last 12 months
• Shift worker
• If unwilling to keep a weighed 7-day food diary