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

This research project will assess how two treatments for irritable bowel syndrome (one dietary and one behavioral) work and for whom. This will be done by assessing moderators (what treatment works for who and in what context) and mediators (how treatment works). Investigators will also assess how the diet and behavioral treatments affect IBS symptoms during treatment. Participants will be randomized to either: i. A FODMAP diet online program that focuses on modifying the consumption of foods high or moderate in fermentable carbohydrates (FODMAPS) to manage IBS symptoms. or, ii. An Exposure-based Cognitive Behavioral Therapy (E-CBT) online program for IBS that focuses on changing symptom-related behaviors which are known to worsen IBS symptoms.