Success in finding an effective treatment strategy for treating functional GI disorders is a challenging area of clinical management. One of the aims of this review was to highlight the importance of assessing the fermentation characteristics of each fiber type when choosing a suitable strategy for patients. When fiber is recommended for FGIDs, use of a soluble supplement such as ispaghula/psyllium is best supported by the available evidence. In constipated patients, it can be helpful for pre-existing hard stool to be eliminated (e.g., with an osmotic laxative) before initiating fiber therapy. Fiber should be started at a nominal dose and slowly titrated up as tolerated over the course of weeks to a target dose of 20–30 g of total dietary and supplementary fiber per day. Even when used judiciously, fiber can exacerbate problems with abdominal distension, flatulence, constipation, and diarrhea. It is clear that rather than extrapolating from the studies undertaken in healthy individuals, further research in functional GI patients should be performed with rigorous endpoints, strict inclusion criteria, and IBS subtype in mind.