There is convincing evidence that patients with functional gastrointestinal disorders (FGIDs) exhibit dysfunctions of the gut involving hypersensitivity and abnormal reflexes, so that physiological, normally unperceived, stimuli induce symptoms. The type of symptoms depends on the specific sensory-reflex pathways and region(s) affected. Fat modulates the responses of the gut to various stimuli, and some of these modulatory mechanisms are abnormal in patients with FGIDs. Indeed, laboratory-based studies have shown that the symptoms experienced by these patients can be induced, or exacerbated, by administration of lipids in amounts that are well tolerated by healthy controls, and, thus, demonstrate a hypersensitivity to lipid. Very few studies have evaluated dietary patterns and eating behavior in these patients, with often-conflicting outcomes, and no studies have been performed to evaluate the role of targeted dietary interventions for the relief of symptoms. Given the evidence from laboratory studies, as well as patient experience, such studies, in large cohorts of patients, are needed with the view to develop personalized, cost-effective treatment approaches. © 2013 by the american College of Gastroenterology.