Lactobacillus acidophilus is a probiotic bacterium commonly used to support gut health. Its use in the context of "leaky gut syndrome"—a term referring to increased intestinal permeability—is primarily supported by modest scientific evidence rather than tradition. Although "leaky gut syndrome" is not formally recognized as a medical diagnosis by all clinicians, increased intestinal permeability is a measurable phenomenon in certain gastrointestinal disorders.

A number of studies have shown that L. acidophilus can help restore the balance of gut microbiota, modulate immune responses, and improve barrier function in the intestinal epithelium. Animal studies and limited human trials suggest that supplementation with L. acidophilus may reduce intestinal inflammation and enhance the expression of tight junction proteins, which are crucial for maintaining gut barrier integrity. For example, a 2012 study in rodents found that L. acidophilus supplementation decreased gut permeability and inflammation. However, robust clinical trials in humans with "leaky gut" specifically are lacking, and most evidence comes from studies in inflammatory bowel disease, irritable bowel syndrome, or animal models.

In summary, while there is some scientific rationale and early evidence supporting the use of L. acidophilus to help with intestinal barrier function, the overall quality and quantity of evidence for "leaky gut syndrome" is limited, meriting a modest evidence rating.