Background <p>Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder in which dietary interventions play a pivotal role in symptom management. Although traditional dietary advice, the low-FODMAP diet (LFD), and the gluten-free diet (GFD) are commonly employed in clinical practice, comparative evidence regarding their relative efficacy—particularly when applied in combination—remains limited.</p> Methods <p>This randomized controlled trial with blinded outcome assessment was conducted in the gastroenterology outpatient clinic of a university hospital. Adult patients aged 19–65&#xa0;years with IBS diagnosed according to the Rome IV criteria were randomized using a minimization method to one of four dietary interventions administered for four weeks: traditional diet (TD), LFD, GFD or a combined low-FODMAP gluten-free diet (LFGFD). Participants were blinded to the specific name of the dietary intervention, and outcome assessors were blinded to group allocation. The primary outcomes were changes in the IBS Symptom Severity Score (IBS-SSS) and the IBS Quality of Life questionnaire (IBS-QOL). Secondary outcomes included changes in FODMAP and gluten intake frequency scores, Bristol Stool Scale, body mass index (BMI), and responder rates.</p> Results <p>Baseline demographic and clinical characteristics were comparable across the four groups. IBS-SSS decreased significantly within all groups following dietary intervention (p ≤ 0.004), with significantly greater reductions observed in the LFD and LFGFD groups compared with the TD group (p = 0.002). IBS-QOL scores improved significantly within all groups (p ≤ 0.003); however, no significant between-group differences were detected (p = 0.082). Clinically meaningful symptom improvement, defined as a reduction of at least 50 points in IBS-SSS, was achieved by all participants in the LFD, GFD, and LFGFD groups, compared with 8 of 13 participants (61.5%) in the TD group (p = 0.001). Changes in BSS and BMI did not differ significantly between groups.</p> Conclusions <p>LFD and LFGFD diets were more effective than traditional dietary advice in reducing IBS symptom severity, whereas all dietary approaches yielded significant within-group improvements in quality of life, with no significant between-group difference detected, indicating that no single dietary strategy demonstrated a clear advantage in this domain. These findings, which reflect the restriction phase only, support a stepwise, individualized dietary management strategy in IBS that balances symptom control with quality-of-life considerations.</p> <p>Clinical trial number: NCT04853381.</p>