First-line therapies for non-constipated irritable bowel syndrome (IBS) includes various diets recommendations despite insufficient or low-quality evidence. A recent study randomized trial compared traditional dietary advice (TDA) against the low FODMAP diet (LFD) and gluten-free diet (GFD). In this study, the patients with Rome IV-defined non-constipated IBS were randomized to TDA, LFD, or a GFD. The primary outcome assessed the clinical response after 4 weeks of dietary intervention, as defined by ≥50-point reduction in IBS symptom severity score (IBS-SSS). The secondary outcomes included variations in individual IBS-SSS items within clinical responders, acceptability and food-related quality of life with dietary therapy, alterations in nutritional intake and stool dysbiosis index and baseline factors associated with clinical response. 

Results showed ≥50-point reduction in IBS-SSS in 42% undertaking TDA, 55% on LFD and 58% taking GFD. Responders showed similar improvements in IBS-SSS items regardless of their allocated diet. 

TDA was found to be cheaper, less time-consuming to shop, and easier to follow when eating out than the GFD and LFD. Compared to LFD, TDA was easier to easier to incorporate in day-to-day life. The overall decrease in micro-and macro-nutrient intake did not greatly differ across the diets. However, the LFD group showed the greatest reduction in total FODMAP content (27.7g/day pre-intervention to 7.6g/day at week 4) than the GFD (27.4/g/day to 22.4g/day) and TDA (24.9g/day to 15.2g/day). Alterations in stool dysbiosis index were identical across the diets, with 22-29%, 35-39% and 35-40% showing reduced dysbiosis, no change and increased dysbiosis, respectively. Baseline clinical characteristics and stool dysbiosis index were not able to predict response to dietary therapy. 

Thus, TDA, LFD and GFD can be regarded as the effective approaches in non-constipated IBS, with TDA being the most patient-friendly concerning cost and convenience. Thus, TDA should be utilized as the first-choice dietary therapy in non-constipated IBS, with an LFD and GFD reserved according to specific patient preferences and specialist dietetic input. 

Source: Rej A, et al. Clin Gastroenterol Hepatol. 2022; S1542-3565(22)00202-6.