Role of the duodenal microbiota in functional dyspepsia

Background Functional dyspepsia (FD) is a common and debilitating gastrointestinal disorder attributed to altered gut‐brain interactions. While the etiology of FD remains unknown, emerging research suggests the mechanisms are likely multifactorial and heterogenous among patient subgroups. Small bowel motor disturbances, visceral hypersensitivity, chronic microinflammation, and increased intestinal tract permeability have all been linked to the pathogenesis of FD. Recently, alterations to the gut microbiome have also been implicated to play an important role in the disease. Changes to the duodenal microbiota may either trigger or be a consequence of immune and neuronal disturbances observed in the disease, but the mechanisms of influence of small intestinal flora on gastrointestinal function and symptomatology are unknown. Purpose This review summarizes and synthesizes the literature on the link between the microbiota, low‐grade inflammatory changes in the duodenum and FD. This review is not intended to provide a complete overview of FD or the small intestinal microbiota, but instead outline some of the key conceptual advances in understanding the interactions between altered gastrointestinal bacterial communities; dietary factors; host immune activation; and stimulation of the gut–brain axes in patients with FD versus controls. Current and emerging treatment approaches such as dietary interventions and antibiotic or probiotic use that have demonstrated symptom benefits for patients are reviewed, and their role in modulating the host–microbiota is discussed. Finally, suggested opportunities for diagnostic and therapeutic improvements for patients with this condition are presented. There is accumulating evidence that microbial colonization of the small intestine plays a role in the pathophysiology of disorders of gut–brain interaction. Functional dyspepsia is characterised in a major subset by low grade duodenal inflammation (eosinophils and mast cells), duodenal dysbiosis and altered mucosal barrier dysfunction. While low‐grade inflammation might be the consequence of microbial dysbiosis, the inflammation may play a key role in sensory dysfunction. This disease process resulting in the manifestation of dyspeptic symptoms is likely modified by environmental factors most notably dietary factors or medications.