Abstract The aim of this review was to examine what existing low FODMAP diet (LFD) trials can tell us about whether reductions in FODMAP intake plausibly explain symptom improvement in irritable bowel syndrome (IBS). Although the LFD is an effective treatment, supported by multiple randomised controlled trials and meta-analyses, the mechanisms through which it exerts its effects remain unclear. Symptom improvement is commonly attributed to reduced FODMAP intake, yet this assumption has rarely been evaluated directly. Using a mediation-informed framework, we examined whether published LFD trials assessed two key elements required to support a mechanistic role for FODMAP intake: whether the intervention altered FODMAP intake ( a path), and whether variation in intake was associated with symptom outcomes independent of intervention group ( b path). We found that evidence for clinical efficacy has not been matched by equivalent evidence explaining how the diet works. While many trials demonstrate that LFD interventions reduce FODMAP intake, few examine whether differences in intake account for differences in symptom improvement between individuals. As a result, it remains uncertain to what extent symptom benefits are driven by FODMAP reduction itself versus other factors accompanying dietary change. Strengthening future trial design to link dietary intake measurement with mechanistic analysis is essential for informing less restrictive, targeted, and personalised dietary strategies in IBS.
Anderson et al. (Thu,) studied this question.