Are you what you eat? How can dietary components influence microbial composition of the gut and function of the peripheral and central nervous system? The gut and brain is linked through complex mechanisms of sensorimotor functions of the immune system, the hypothalamic-pituitary-adrenal-axis, the enteric nervous system and microbiota.

In this project, a multitude of factors contributing to the bidirectional neurobiological communication along the brain-but-axis will be investigated. No disease of the brain-gut axis has been elucidated, therefore our investigations involves approaching a large span of components and processes involved in the axis. This study is carried out as a case-report study (baseline, IBS n=100, healthy controls n=40) followed by a dietary intervention (IBS-D n=60). Through multivariate analyses, the investigators will identify patterns of factors contributing to patient symptomatology and pathology, followed by big data analysis leading to stratification of sub-classification of irritable bowel syndrome (IBS).

Data from deep phenotype characterization of 100 patients with IBS and 40 healthy age (between 18 and 65) and gender-matched controls will be collected between May 2019 and December 2021. Psychometric tests, questionnaires, biological samples (blood, faeces, saliva and GI biopsies from antrum, duodenum and sigmoid colon), assessment of gastric accommodation and emptying using transabdominal ultrasound, vagal activity, and functional and structural magnetic resonance imaging (MRI) of the brain, will be carried out. A subgroup of 60 patients with IBS-D will be further included in a 12-week low Fermentable Oligo-, Di-, Mono-saccharides And Polyols (FODMAP) dietary intervention-study to determine short and long-term effects of diet on symptoms, microbiota composition, molecular GI signatures, cognition and behavioural traits, and structural and functional brain signatures. Deep machine learning, prediction tools and big data analysis will be used for multivariate analysis allowing disease stratification and diagnostic biomarker detection.

Inclusion Criteria:

• Subject must be between 18 and 65 years of age

• Fulfil the ROME-IV criteria for IBS

  1. Had recurrent abdominal pain on average at least 1 day per week during the previous 3 months that is associated with alterations in bowel habits.
  2. Duration at least six months.

Exclusion Criteria:

• Pharmacological treatment affecting the GI-tract, including treatment for depression

• Organic disease:

  1. coeliac disease
  2. inflammatory bowel disease
  3. neurological diseases
  4. diabetes
  5. active helicobacter pylori infection
  6. polycystic ovary syndrome

• Treated with systemic antibiotics within the last 3 months

• Use painkillers regularly, other than paracetamol

• Pregnant

• Previous intestinal surgery (appendectomy is OK)

• Claustrophobic or have metallic implants that are not MR compatible

• Vegan or vegetarian

• Been travelling outside Europe within the last three weeks (or plan to travel in the nearest future)

• Probiotics or lowFODMAP-diet within the last three weeks

• Participation in any other simultaneous clinical study

• Inability to comprehend and respond to questionnaires or follow dietary guidance

De-identified stool samples, blood chemistry and symptom severity scores will be shared with collaborators.

The data will become available post microbiota-analysis until the end of the study period.