Lactobacillus reuteri is a probiotic bacterium that has been studied for its role in supporting gastrointestinal health, including the small intestine. Scientific evidence suggests that L. reuteri may help maintain the integrity of the intestinal barrier, modulate immune responses, and inhibit the growth of pathogenic microbes in the small intestine. Several clinical trials and animal studies have indicated that supplementation with L. reuteri can alleviate symptoms of small intestinal disorders such as irritable bowel syndrome (IBS), small intestinal bacterial overgrowth (SIBO), and diarrhea, especially in children.

Mechanistically, L. reuteri produces reuterin, an antimicrobial substance that can suppress harmful bacteria and support a healthy microbiota balance. Some studies have also shown that L. reuteri can reduce inflammation in the gut by modulating cytokine production and promoting regulatory T-cell responses.

The overall evidence base is moderate: while some randomized controlled trials and meta-analyses report beneficial effects, findings are not always consistent, and more high-quality studies specific to the small intestine are needed. Nevertheless, its use is scientifically justified for general small intestinal support, particularly in contexts of dysbiosis or mild inflammatory conditions.