Exclude or Expose in Irritable Bowel Syndrome: What Works for Whom and How?

Inclusion Criteria: Each participant must meet all of the following criteria to be enrolled in this trial: * Living in Australia or the United States * Aged 18 years or older * Body Mass Index (BMI) \[Equation\]18.5kg/m2 and \[Equation\] 34.9kg/m2 * Diagnosed with IBS by a General Practitioner, Family Physician, or Gastroenterologist, or Advanced Specialist Dietitian * Currently fulfill Rome IV criteria for IBS * Symptomatic at the time of recruitment (IBS-SSS \> 175) * Access to a computer and internet * Sufficient English language and computer skills to complete a text-based online treatment * Willing to make dietary or behavioral changes in line with the allocated treatment program * Ability to provide informed consent Exclusion Criteria:Patients meeting any of the following criteria will be excluded from the trial: * Presence or known history of other GI disease (e.g. coeliac disease, Inflammatory Bowel Disease) or history of gastrointestinal cancer * History of major gastrointestinal surgery (not appendectomy, cholecystectomy or hemorrhoidectomy) * Individuals who report alarm symptoms (e.g., blood in stool, recent unexplained/unintentional weight loss \>5% body weight, a recent change in bowel habits if \>50 years, family history of gastrointestinal cancer or gastrointestinal diseases, large volumes of diarrhea occurring at night, fever associated with gut symptoms, recurrent vomiting, persistent unexplained iron deficiency) will be excluded if appropriate medical investigations have not been conducted, unless written medical approval is provided from a general practitioner, family physical, or gastroenterologist. * Diagnosis of major disease that could explain current gastrointestinal symptoms such as severe diabetic, cardiac, liver, neurological, neuropathy disease * History or current diagnosis of psychotic disorder or bipolar disorder * Current diagnosis of substance abuse disorder or major depressive disorder or active suicidal ideation * History or current diagnosis of an eating disorder * Current enteral/parenteral feeding or use of supplemental feeds (e.g. Ensure) * Pregnant or lactating or planning to become pregnant during the 12-week intervention period * Commenced or change in dose of antibiotics and medications that potentially affect the gastrointestinal transit (e.g. anti-diarrheals and laxatives) in the 3 months preceding study commencement. * Commenced taking or changed dose of probiotics, prebiotics, fibre supplements and digestive enzymes in the 3 months preceding study commencement * Commenced or change dose in psychotropic medication in the 3 months preceding study commencement * Are currently undertaking behavioral therapy for IBS (including cognitive behavioral therapy, CBT), or have undertaken clinician-delivered behavioral therapy for the treatment of IBS * Are currently undertaking or have undertaken a dietitian-prescribed and delivered restrictive diet for IBS (e.g., FODMAP diet).