Microbiota and Nutritional Changes Following a Low-FODMAP Diet in Patients with Ulcerative Colitis and Irritable Bowel Syndrome: A Randomized Controlled Trial

The low-FODMAP diet (LFD) reduces gastrointestinal symptoms, restricting poorly absorbed short-chain carbohydrates to reduce colonic fermentation. It has been proposed as a dietary strategy for irritable bowel syndrome (IBS) and ulcerative colitis (UC) patients. However, this diet could affect patients’ nutritional status and alter their gut microbiota. We aimed to evaluate the effects of a 10-week LFD on nutritional status, quality of life, and gut microbiota in patients with IBS, UC, and a control group without gastrointestinal symptoms. A randomized, single-blind clinical trial was conducted, including adults with IBS and UC, as well as a control group. Participants were randomly assigned to receive either an LFD or a standard diet (STD). Nutritional status, stool consistency, bowel habits, and quality of life were assessed, and stool samples were collected. Stool microbiota was profiled by 16S rRNA gene sequencing (V3) and analyzed for alpha diversity, beta diversity and differential abundance. Body composition was assessed by bioelectrical impedance. The follow-up period lasted 10 weeks (W0 to W10). Analyses were conducted in the per-protocol population. In total, 86 patients were included (IBS n = 40, UC n = 34, Control n = 12) with an average age of 40 ± 11 years. After adjustment for baseline values, no statistically significant differences in anthropometric or body-composition outcomes were observed between the LFD and STD groups. Similarly, there was a notable reduction in diarrhea frequency (53.3% vs. 20%, p = 0.058). Additionally, patients with IBS and UC exhibited similar microbiota profiles at W0. Among UC patients following the LFD, there was increased presence of BX12, CAG-1427, Holdemania, Evtepia, and Granulicatella, while Angelakisella and CAG-177 were less abundant. LFD was associated with changes in stool consistency, bowel habits, quality of life, and gut microbiota in patients with UC and IBS.