Vanner, Stephen

AbstractBackgroundThere is compelling evidence that microbe‐host interactions in the intestinal tract underlie many human disorders, including disorders of gut‐brain interactions (previously termed functional bowel disorders), such as irritable bowel syndrome (IBS). Small intestinal bacterial overgrowth (SIBO) has been recognized for over a century in patients with predisposing conditions causing intestinal stasis, such as surgical alteration of the small bowel or chronic diseases, including scleroderma and is associated with diarrhea and signs of malabsorption. Over 20 years ago, it was hypothesized that increased numbers of small intestine bacteria might also account for symptoms in the absence of malabsorption in IBS and related disorders. This SIBO‐IBS hypothesis stimulated significant research and helped focus the profession's attention on the importance of microbe‐host interactions as a potential pathophysiological mechanism in IBS.PurposeHowever, after two decades, this hypothesis remains unproven. Moreover, it has led to serious unintended consequences, namely the widespread use of unreliable and unvalidated breath tests as a diagnostic test for SIBO and a resultant injudicious use of antibiotics. In this review, we examine why the SIBO hypothesis remains unproven and, given the unintended consequences, discuss why it is time to reject this hypothesis and its reliance on breath testing. We also examine recent IBS studies of bacterial communities in the GI tract, their composition and functions, and their interactions with the host. While these studies provide important insights to guide future research, they highlight the need for further mechanistic studies of microbe‐host interactions in IBS patients before we can understand their possible role in diagnosis and treatment of patient with IBS and related disorders.

LINKED CONTENTThis article is linked to Wang et al and Rej et al papers. To view these articles, visit https://doi.org/10.1111/apt.15419 and https://doi.org/10.1111/apt.15517.

Summary 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.