Tannin Phytocomplex Improves IBS-D Symptoms and Gut-Brain Markers: Prospective Pilot Study

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a multifactorial disorder involving gut-brain axis dysregulation, altered barrier integrity, microbial imbalance, and stress-related mechanisms, with limited nutritional strategies targeting these pathways. Tannin-rich extracts may exert barrier-protective, microbiota-modulating, and stress-related effects. In a prospective before-after pilot study (NCT05207618), 28 adults with IBS‑D completed a 60‑day tannin-based supplementation (480 mg/day). Outcomes included IBS Severity Scoring System (IBS-SSS), bowel habits, somatization, perceived stress, serum zonulin, faecal short-chain fatty acids, and hydrogen breath test. Linear mixed models assessed changes over time. IBS-SSS decreased by an estimated mean of 70 points (95% CI: 34-107; p < 0.0001); stool consistency improved by 1.38 (95% CI: 0.72 to 2.05; p < 0.0001), and bowel movements/day decreased by 0.84 (95% CI: 0.08 to 1.71; P = 0.028). Somatization and stress scores declined significantly (both P ≤ 0.003). Zonulin dropped (P < 0.0001), butyrate increased (p = 0.001), and propionate decreased (p = 0.017). Hydrogen-positive subjects at baseline (3/28) were all negative at 60 days. No adverse events occurred. This pilot suggests a tannin-based phytocomplex may improve gastrointestinal and psychological symptoms in IBS-D, with biomarker changes indicating enhanced barrier function and microbial metabolism. Larger trials are warranted.