Efficacy and acceptability of dietary therapies in non-constipated irritable bowel syndrome : a randomized trial of traditional dietary advice, the low FODMAP diet and the gluten-free diet

Background & Aims

Various diets are proposed as first-line therapies for non-constipated irritable bowel syndrome (IBS) despite insufficient or low-quality evidence. We performed a randomized trial comparing traditional dietary advice (TDA) against the low FODMAP diet (LFD) and gluten-free diet (GFD).

Methods

Patients with Rome IV-defined non-constipated IBS were randomized to TDA, LFD, or a GFD (the latter allowing for minute gluten cross-contamination). The primary endpoint was clinical response after 4 weeks of dietary intervention, as defined by ≥50-point reduction in IBS symptom severity score (IBS-SSS). Secondary endpoints included i) changes in individual IBS-SSS items within clinical responders, ii) acceptability and food-related quality of life with dietary therapy, iii) changes in nutritional intake, iv) alterations in stool dysbiosis index, and v) baseline factors associated with clinical response.

Results

The primary endpoint of ≥50-point reduction in IBS-SSS was met by 42% (n=14/33) undertaking TDA, 55% (n=18/33) for LFD, and 58% (n=19/33) for GFD; p=0.43. Responders had similar improvements in IBS-SSS items regardless of their allocated diet. Individuals found TDA cheaper (p<0.01), less time-consuming to shop (p<0.01), and easier to follow when eating out (p=0.03) than the GFD and LFD. TDA was also easier to incorporate into daily life than the LFD (p=0.02). Overall reductions in micro- and macro- nutrient intake did not significantly differ across the diets. However, the LFD group had the greatest reduction in total FODMAP content (27.7g/day pre-intervention to 7.6g/day at week 4) compared with the GFD (27.4/g/day to 22.4g/day) and TDA (24.9g/day to 15.2g/day); p<0.01. Alterations in stool dysbiosis index were similar across the diets, with 22-29% showing reduced dysbiosis, 35-39% no change, and 35-40% increased dysbiosis; p=0.99. Baseline clinical characteristics and stool dysbiosis index did not predict response to dietary therapy.

Conclusion

TDA, LFD and GFD are effective approaches in non-constipated IBS, but TDA is the most patient-friendly in terms of cost and convenience. We recommend TDA as the first-choice dietary therapy in non-constipated IBS, with a LFD and GFD reserved according to specific patient preferences and specialist dietetic input.