Effect of Exclusion Diets on Symptom Severity and the Gut Microbiota in Patients with Irritable Bowel Syndrome

Abstract: Background & Aims Altered fecal microbiota have been reported in IBS, although studies vary which could be due to dietary effects. Many IBS patients may eliminate certain foods because of their symptoms, which in turn may alter fecal microbiota diversity and composition. This study aims were to determine if dietary patterns were associated with IBS, symptoms, and fecal microbiota differences reported in IBS. Methods 346 IBS participants and 170 healthy controls (HCs) completed a Diet Checklist reflecting the diet(s) consumed most frequently. An exclusion diet was defined as a diet that eliminated food components by choice. Within this group, a gluten-free, dairy-free, or low FODMAP diet was further defined as restrictive as they are often implicated to reduce symptoms. Stool samples were obtained from 171 IBS patients and 98 HCs for 16S rRNA gene sequencing and microbial composition analysis. Results Having IBS symptoms was associated with consuming a restrictive diet (27.17% of IBS patients vs 7.65% of HCs; OR 3.25; 95% CI 1.66-6.75; p-value 0.006). IBS participants on an exclusion or restrictive diet reported more severe IBS symptoms (p=0.042 and p=0.029 respectively). The composition of the microbiota in IBS patients varied depending on the diet consumed. IBS participants on an exclusion diet had a greater abundance of Lachnospira and a lower abundance of Eubacterium (q-values Conclusions Restrictive diets are likely consumed more by IBS patients than HCs to reduce GI symptom severity. Dietary patterns influence the composition of fecal microbiota and may explain some of the differences between IBS and HCs.