Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction associated with reduced quality of life and healthcare utilisation. The low FODMAP (LFD) diet is an effective treatment for IBS, but only 50-80% of patients achieve clinically meaningful symptom improvement (1). Identifying predictors, moderators and mediators may help determine who is most likely to benefit from treatment and how treatment effects occur, supporting personalised dietary care. However, the nature, credibility and clinical applicability of this evidence remain unclear. We conducted a scoping review to characterise predictors, moderators and mediators of gastrointestinal symptom outcomes following LFD interventions in adults with IBS, and to evaluate the methodological credibility and interpretation of the evidence. MEDLINE, EMBASE and CENTRAL were searched from inception to June 2026. Studies evaluating baseline predictors or moderators of gastrointestinal symptom outcomes following low FODMAP (LFD) diet interventions; or conducting formal mediation analyses were eligible. Predictor analyses were synthesised using an evidence tier framework spanning exploratory association studies to prediction models. Credibility and interpretation of reported findings were evaluated using structured appraisal frameworks (2,3). The search identified 3241 records of which 1978 were screened and 29 studies (18 randomised trials and 11 observational studies) met the inclusion criteria. Candidate predictors spanned eight domains, most commonly microbiota (n = 13), clinical (n = 11), sociodemographic (n = 10) and psychological (n = 10), with fewer studies investigating physiological (n = 6), dietary (n = 6), metabolomic (n = 3), and genetic (n = 2) predictors. Despite numerous candidate predictors, only six studies (21%) conducted multivariable analyses, and 5 (17%) developed prediction models. Positive signals were identified across all domains, but were heterogeneous and typically isolated, with no prediction model undergoing external validation. Methodological credibility was generally low, reflecting limited pre-specification of candidate predictors or moderators and analytical approaches, small sample sizes relative to analytical complexity, inadequate management of multiplicity, incomplete reporting, and limited replication or validation of reported findings. Three studies evaluated moderators of treatment response, only two using formal interaction analyses, while no eligible mediation analyses were identified. Although many authors appropriately acknowledged the preliminary nature of their findings, some interpretations implied greater predictive utility or treatment-selection relevance than was supported by the underlying evidence. Despite interest in personalised nutrition for IBS, research has largely remained at the stage of candidate predictor discovery rather than progressing towards clinically applicable prediction. The principal barrier to translation is the limited progression from exploratory association studies to externally validated prediction models, and limited evidence for treatment-effect modification and mediation. Future research should combine identification of candidate predictors with prospectively specified, adequately powered studies, rigorous model development and external validation, alongside robust evaluation of moderators and mediators, to enable personalised dietary treatment selection.