Functional bowel symptoms and diet.

It is well recognised that ingestion of food is a trigger for functional bowel symptoms, particularly those associated with irritable bowel syndrome (IBS). Patients often use manipulation of diet as a means of controlling symptoms. Despite description of multiple dietary methods, few have scientific backing or quality evidence of efficacy. One approach is to define how specific food components influence the pathophysiology of IBS and then rationally design dietary approaches. For example, short-chain poorly absorbed carbohydrates (fermentable oligo-, di- and mono-saccharides and polyols (FODMAP)) cause luminal distension, which is a major stimulus for the development of symptoms in patients with visceral hypersensitivity. By determining food content of FODMAP, a diet in which foods low in FODMAP are favoured over those high in FODMAP can be designed. Observational, comparative and randomised controlled treatment and rechallenge studies have shown that such an approach is efficacious in the majority of patients with IBS. The low FODMAP diet is now the primary dietary therapy for such patients. Similar approaches can be applied to other food components, including proteins (such as gluten), fats and natural bioactive food chemicals. Such approaches have suggestions of efficacy, but the evidence base remains underdeveloped. An additional and important consideration for any dietary therapy is its nutritional adequacy and potential adverse health effects. Dietary manipulation is now a key management strategy in patients with functional bowel symptoms. Future well-designed interventional studies will lead to refinement of dietary approaches taken and to a better understanding of their long-term safety.