The efficacy of a diet low in fermentable oligo-, di-, monosaccharides and polyols in irritable bowel syndrome compared to its "real-world" effectiveness: a systematic review protocol (Preprint)

BACKGROUND Irritable bowel syndrome is associated with various, sometimes severe, gastrointestinal and non-gastrointestinal symptoms, reduced quality of life and increased use of health care services. A diet low in fermentable oligo-, di-, monosaccharides, and polyols (low FODMAP diet) is one therapeutic option to improve patients' symptoms and quality of life listed in several guidelines. Health service research distinguishes between efficacy studies assessing the efficiency of new interventions under ideal conditions and effectiveness studies measuring the same interventions' efficiency in everyday practice. Efficacy studies tend to overestimate the efficiency; this phenomenon is called the efficacy-effectiveness gap. OBJECTIVE This systematic review aims to compare the efficacy of the low FODMAP diet from efficacy RCTs with the effectiveness of "real world" studies. METHODS To account for the differences between efficacy and “real-world” studies, two PICOS (Population, Intervention, Comparison, Outcomes and Study design) will be applied. The first PICOS includes randomised controlled trials on the low FODMAP diet's efficacy. The second PICOS focuses on the low FODMAP diet's effectiveness in real-world settings. The following databases will be searched: EMBASE, MEDLINE, CENTRAL and CINAHL. Two independent reviewers will perform study selection, data extraction, risk of bias assessment, and assess selected quality aspects from GRADE. Outcomes assessed are stool frequency, stool consistencies, abdominal pain (critical outcomes), overall symptom score, adequate symptom relief, IBS-specific quality of life, and diet adherence (important outcomes). Data will be summarised with forest plots without summary statistics, tables and narrative descriptions. RESULTS The search, title and abstract, and full-text screening were completed in March 2021 and an update search was done in May 2022. As of July 2022, we are in the progress of completing data extraction and quality assessment. CONCLUSIONS The findings of this systematic review will summarize the current evidence on the low FODMAP diet in IBS and compare its efficacy in randomized controlled trials to its real-life effectiveness. Our data will allow dietitians to compare their outcomes with this systematic review. CLINICALTRIAL PROSPERO registration number: CRD42021278952