Functional Dyspepsia and the Upper GI Microbiome

Functional dyspepsia (FD) affects 10-20% of the global population and is defined by persistent epigastric symptoms — early satiety, postprandial fullness, epigastric pain/burning — in the absence of structural abnormality on upper endoscopy. While historically managed as a motility or acid secretion disorder, emerging evidence positions upper GI microbiome dysbiosis as a central pathophysiological driver in a significant proportion of FD patients.

The Duodenal Microbiome in FD

The duodenum is the least-studied GI segment microbiologically, yet duodenal microbiome analysis in FD reveals consistent abnormalities: increased Proteobacteria (particularly Escherichia, Streptococcus), reduced commensal diversity, and evidence of low-grade duodenal eosinophilia and mast cell activation. These findings suggest duodenal dysbiosis drives mucosal immune activation that sensitizes visceral afferents — the mechanism underlying visceral hypersensitivity.

H. pylori and the Gastric Microbiome

Helicobacter pylori infection disrupts the gastric microbiome beyond its direct pathogenic effects. H. pylori eradication, while clinically necessary, produces a secondary dysbiosis requiring active microbiome restoration. Post-eradication, gastric pH normalization allows recolonization by colonizing commensals; probiotic supplementation during and after eradication therapy reduces treatment side effects and supports microbiome recovery. Lactobacillus strains improve eradication rates when combined with standard triple therapy (Zheng et al., Helicobacter, 2013).

SIBO as an FD Driver

SIBO is present in 30-40% of FD patients — a prevalence far above population baseline. Small intestinal bacterial overgrowth in the duodenum and proximal jejunum generates excess fermentation gas, alters CCK release, and impairs motilin-mediated gastric emptying, directly producing postprandial bloating and early satiety. Rifaximin treatment resolves FD symptoms in a substantial proportion of SIBO-positive FD patients. See our SIBO article for diagnostic and treatment protocols.