Review article: biological mechanisms for symptom causation by individual FODMAP subgroups - the case for a more personalised approach to dietary restriction

Background: Due to the paucity of targeted therapy for irritable bowel syndrome (IBS), many patients turn to dietary modifications for symptom management. The combination of five subgroups of poorly absorbed and rapidly fermented carbohydrates—fructans, galacto-oligosaccharides, lactose, excess fructose and polyols—are thought to trigger gastrointestinal symptoms and are referred to collectively as “FODMAPs”. Aims: To examine the biological plausibility and mechanisms by which foods high in specific FODMAP subgroups cause symptoms, and to use this information to explore the possibility of targeting select dietary components to allow for a more personalised approach to dietary adjustment. Methods: Recent literature was analysed via search databases including Medline, PubMed and Scopus. Results: Lactose, fructans and galacto-oligosaccharides have strong biologic plausibility for symptom generation due to lack of hydrolases resulting in distention from osmosis and rapid fermentation. However, excess fructose and polyols may only cause symptoms in specific individuals when consumed in high doses, but this remains to be established. There is evidence to suggest that certain patient characteristics such as ethnicity may predict response to lactose, but differentiation of other subgroups is difficult prior to dietary manipulation. Conclusions: While some clear mechanisms of action for symptom generation have been established, further research is needed to understand which patients will respond to specific FODMAP subgroup restriction. We suggest that clinicians consider in some patients a tailored, personalised “bottom-up” approach to the low-FODMAP diet, such as dietary restriction relevant to the patients’ ethnicity, symptom profile and usual dietary intake.