16S metagenomic sequences from IBS patients before and after dietary intervention with Low Fodmap or control sham diet, with and without supplementation with probiotic or placebo Raw sequence reads. Fondazione Edmund Mach

Feeding studies demonstrate the clinical potential of restriction of fermentable carbohydrates (low FODMAP diet, LFD) in irritable bowel syndrome (IBS). However, a placebo-controlled dietary advice study has not been conducted and the diet leads to a potentially detrimental shift in microbiota composition.Methods: A 2x2 factorial trial was undertaken in the tertiary care setting. Patients aged 18-65 years with Rome III IBS were recruited. Patients were randomised 1:1 for four weeks to a diet (sham diet vs LFD) and supplement (placebo vs probiotic), resulting in four different groups. The sham diet was equivalent in dietary restriction compared with LFD. The probiotic was multistrain (VSL#3). Patients were masked to the interventions. The primary endpoints were adequate relief of symptoms and stool Bifidobacteria abundance at four weeks.This is the first placebo-controlled study of LFD advice in IBS, reporting adequate symptom relief that approached significance together with significantly reduced symptom scores compared with placebo. Probiotic co-administration ameliorated the diet-induced decline in Bifidobacteria abundance.