Lactobacillus johnsonii is a probiotic bacterium that has received scientific attention for its potential benefits to the small intestine and gastrointestinal health. Several animal and human studies have indicated that L. johnsonii may help maintain intestinal barrier integrity, modulate immune responses, and inhibit the growth of certain pathogenic bacteria within the small intestine. For example, research published in Gut Microbes (2012) and Beneficial Microbes (2020) suggests that supplementation with L. johnsonii can reduce intestinal inflammation and improve the composition of gut microbiota. The strain L. johnsonii NCC 533, in particular, has been studied for its ability to enhance mucosal immune function and protect against gastrointestinal infections in animal models.

In humans, some small clinical trials have observed that L. johnsonii supplementation may help relieve mild gastrointestinal symptoms, such as bloating and discomfort, though more robust, large-scale studies are needed to confirm these effects specifically in the small intestine. The evidence is not as strong or consistent as for some other probiotics, but the available research provides moderate support for the use of L. johnsonii in maintaining small intestinal health, particularly in the context of supporting a balanced microbiome and modulating inflammation. Therefore, use of this probiotic for small intestinal support is justified by a moderate level of scientific evidence.