Saccharomyces boulardii is a probiotic yeast widely studied for its beneficial effects on gastrointestinal health, particularly in the prevention and treatment of diarrhea and certain intestinal infections. The connection to Peyer’s patches, which are lymphoid tissues in the small intestine that play a critical role in mucosal immunity, is based on mechanistic and animal studies demonstrating S. boulardii’s ability to modulate the gut immune system.

Several studies have shown that S. boulardii can enhance intestinal immune responses by stimulating the secretion of immunoglobulin A (IgA) and modulating cytokine production. Some animal studies suggest that S. boulardii administration increases the size and activity of Peyer’s patches and enhances antigen sampling and processing. These effects are thought to contribute to its ability to support the gut-associated lymphoid tissue (GALT), of which Peyer’s patches are a key component. For example, a 2007 study in mice found increased IgA-secreting cells in Peyer’s patches after oral administration of S. boulardii.

However, while these findings are promising, direct clinical evidence in humans specifically demonstrating support for Peyer’s patches function is limited. Most human trials focus on clinical outcomes like reduced incidence of diarrhea or infection, rather than direct measurement of Peyer’s patches activity. Thus, the evidence is moderate and mechanistically plausible, but more direct human studies would strengthen the case.