Evidence that independent gut-to-brain and brain-to-gut pathways operate in the irritable bowel syndrome and functional dyspepsia: a 1-year population-based prospective study

Background: Traditionally, functional gastrointestinal disorders (FGIDs) are conceptualised as originating in the brain via stress pathways (brain-to-gut). It is uncertain how many with irritable bowel syndrome (IBS) and functional dyspepsia (FD) have a gut origin of symptoms (gut-to-brain pathway). Aims: To determine if there is a distinct brain-to-gut FGID (where psychological symptoms begin first) and separately a distinct gut-to-brain FGID (where gut symptoms start first). Methods: A prospective random population sample from Newcastle, Australia who responded to a validated survey in 2012 and completed a 1-year follow-up survey (n = 1900). The surveys contained questions on Rome III IBS and FD and the Hospital Anxiety and Depression Scale. Results: We found that higher levels of anxiety and depression at baseline were significant predictors of developing IBS (OR = 1.31; 95% CI 1.06–1.61, P = 0.01; OR = 1.54; 95% CI 1.29–1.83, P < 0.001) and FD (OR = 1.28; 95% CI 1.05–1.55, P = 0.01; OR = 1.55, 95% CI 1.32–1.83, P < 0.001), respectively, at the 1-year follow-up. Among those people who did not have elevated levels of anxiety and depression at baseline, subjects at baseline with documented IBS (mean difference 0.34; 95% CI 0.13–0.55, P = 0.002; 0.81; 95% CI 0.47–1.15, P < 0.001) and FD (0.38; 95% CI 0.14–0.63, P = 0.002; 0.92; 95% CI 0.57–1.27, P < 0.001), reported significantly higher levels of anxiety and depression at the 1-year follow-up. We calculated in one-third of individuals a mood disorder precedes FGID but in two-thirds an FGID precedes the mood disorder. Conclusion: While brain–gut pathways are bidirectional, a major subset begin with gut symptoms first and only then psychological distress develops, implicating primary gut mechanisms as drivers of the gut and extra-intestinal features in many cases.