CONSORT checklist.

<div><p>Background</p><p>An increased intestinal permeability is a common feature in patients with diarrhoea-predominant irritable bowel syndrome (IBS-D). Probiotics have shown to improve IBS symptoms and might also affect intestinal barrier function.</p><p>Aim</p><p>The aim of this study was to investigate the effects of a 6-week intervention with <i>Limosilactobacillus reuteri</i> ATCC PTA 6475 alone (single strain) or in combination with <i>Limosilactobacillus reuteri</i> DSM 17938 (dual strain) on gut barrier function, immune markers, and symptoms in IBS-D patients (ClinicalTrials.gov registration number: NCT03986476).</p><p>Methods</p><p>65 IBS-D patients were randomised into three groups (placebo, single strain, dual strain). Small and large intestinal permeability were assessed using a multi-sugar urinary recovery test. Blood, saliva, faecal samples, and several symptom scales were collected before, and after three and six weeks of intervention.</p><p>Results</p><p>Small and large intestinal permeability as well as other markers of gut barrier function were not significantly affected by the probiotic interventions. Serum IL-6 levels showed a tendency to be reduced in the single strain group (descriptive p = 0.052). In addition, high-sensitivity C-reactive protein was significantly reduced in the dual strain group (p = 0.041). The participants in both treatment groups reported less gastrointestinal symptoms after three weeks, but this reached significance only in the dual strain group (total score: p = 0.032, pain subscore: p = 0.028). After six weeks, none of the assessed symptoms were significantly different from the placebo.</p><p>Conclusion</p><p>The probiotic compounds investigated in this study did not seem to affect IBS-D patients’ gut barrier function, but showed potential anti-inflammatory and symptom-improving properties, which need to be confirmed in larger study cohorts.</p></div>