Saccharomyces boulardii is a probiotic yeast that has been extensively studied and is scientifically validated for supporting the health of the small intestine, particularly in the context of gastrointestinal disorders. Multiple randomized controlled trials and meta-analyses have demonstrated its efficacy in reducing the duration and severity of acute diarrhea, including antibiotic-associated diarrhea and infectious diarrhea, which often affect the small intestine. S. boulardii exerts its beneficial effects by modulating the intestinal microbiota, enhancing mucosal immunity, and inhibiting the adherence and effects of pathogenic bacteria and their toxins. In addition, it helps maintain and restore the integrity of the intestinal epithelial barrier, which is crucial for the small intestine’s function.

Clinical guidelines and systematic reviews (e.g., McFarland LV, 2010, "Systematic review and meta-analysis of Saccharomyces boulardii in adult patients," World Journal of Gastroenterology) support its use for preventing and treating antibiotic-associated diarrhea and Clostridioides difficile infection recurrence. There is also evidence for its use in travelers’ diarrhea and some forms of inflammatory bowel disease, though the evidence is stronger for diarrhea-related conditions.

While not a panacea, the weight of scientific evidence supports the use of S. boulardii as an adjunct to conventional therapies for promoting and maintaining small intestinal health, particularly in the context of infections and disruptions to the normal microbiota.