Introduction

Patients (pts) with disorders of gut–brain interaction (DGBI) frequently present with overlapping non-gastrointestinal conditions such as fibromyalgia (FM), whose prevalence in irritable bowel syndrome (IBS) varies from 28–33% to 65%. The co-presence of FM complicates clinical management and worsens outcomes. The pathophysiology of IBS is now well established, involving dysfunction of the gut-brain axis and peripheral factors including microbiome alterations, mucosal barrier disruption, and immune activation. Recently, dysfunction of the gut-musculoskeletal axis was proposed for FM. Shared pathophysiology, involving altered intestinal permeability (IP), and multidisciplinary therapeutic strategies, including dietary interventions, have been proposed for both conditions.

Aims & Methods

To evaluate the effects of a low-FODMAP diet (LFD) on clinical symptoms and IP in pts with IBS, FM, or both, and to assess correlations with serum biomarkers.
This prospective study included 35 pts (88,6% female): 45.7% had IBS+FM, 28.6% IBS-only, and 25.7% FM-only. IP was assessed using serum zonulin (ZO) levels. Clinical evaluations included: SF-36 (quality of life, QoL) for all pts; IBS Symptom Severity Score (IBS-SSS) for IBS; and both Fibromyalgia Impact Questionnaire (FIQ) and Polysymptomatic Distress Scale (PDS) for FM. Assessments occurred at baseline (T0), after 1 month of LFD (T1), at 3 months (T2, reintroduction phase), and 6 months (T3, free diet/follow-up).

Results

At baseline, QoL was significantly lower in the IBS+FM group compared to IBS-only, especially in physical functioning, social functioning, and general health domains (p<0.001). The IBS-only group showed global QoL improvement after 1 month on the LFD, with significant gains in general health (p=0.02) and emotional well-being (p=0.002). Improvements were sustained through T2, but did not increase further. In contrast, the IBS+FM group demonstrated delayed but significant improvements at T2 in physical functioning (p=0.01), energy/fatigue (p=0.02), and social functioning (p<0.001) domains. Similarly, IBS-SSS scores improved significantly at T1 in the IBS-only group (p<0.001) and remained low at T2 (p=0.006), while in the IBS+FM group, the improvement occurred later, reaching significance at T2 (p=0.02). For FM, FIQ and PDS scores improved significantly only at T3 in the IBS+FM group (p=0.03 and p=0.006, respectively), while no significant change occurred in the FM-only group. However, in this group of pts a non-significant reduction in FM symptom scores was observed at T1 and T2, but was followed by worsening symptoms during the free-diet follow-up at T3. Serum ZO levels at T0 were similar across all groups. Significant reductions were observed only in the FM-only and IBS+FM pts, both at T1 (p< 0.001 for both) and T2 (p=0.004, p=0.01, respectively), suggesting improved intestinal permeability. No significant ZO changes were instead observed in the IBS-only group.

Conclusion

The low-FODMAP diet improves gastrointestinal symptoms and quality of life in IBS patients, especially in general health and emotional well-being domains, with delayed but significant benefits also in those with FM. Reductions in zonulin levels in FM and IBS+FM groups suggest enhanced intestinal barrier function, though not directly tied to symptom relief. These findings support a role for central sensitization in FM and underscore the importance of a multidisciplinary approach for managing overlapping DGBI and FM.