Lactobacillus (various species) is commonly used in probiotic supplements aimed at supporting gut health, including conditions referred to as "Leaky Gut Syndrome" (increased intestinal permeability). While "Leaky Gut Syndrome" is not formally recognized as a distinct medical diagnosis in conventional medicine, increased intestinal permeability is a measurable phenomenon and has been studied in relation to various gastrointestinal and systemic conditions.

Scientific evidence for the use of Lactobacillus in supporting or restoring intestinal barrier function is moderate but promising. Several animal and human studies have shown that certain Lactobacillus strains can improve tight junction integrity, reduce intestinal permeability, and modulate inflammation in the gut. For example, studies have documented that Lactobacillus rhamnosus GG and Lactobacillus plantarum can enhance the expression of proteins that maintain the epithelial barrier and decrease markers of permeability and inflammation in various models.

However, most human clinical trials focus on populations with specific gut disorders (such as irritable bowel syndrome, inflammatory bowel disease, or after antibiotic use) rather than "Leaky Gut Syndrome" per se. The quality and consistency of evidence for use in otherwise healthy individuals or those with unexplained "leaky gut" symptoms remains limited. Thus, while there is a scientific basis for Lactobacillus species in improving gut barrier function, more high-quality, targeted clinical studies are needed to clarify their efficacy specifically for "Leaky Gut Syndrome."