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
