Glycomacropeptide (GMP) is a bioactive peptide derived from κ-casein during cheese production and is notable for its impact on the gut-associated lymphoid tissue (GALT), specifically Peyer’s patches. Scientific studies—primarily in animal models and in vitro systems—have demonstrated that GMP can modulate immune responses. Peyer’s patches are clusters of lymphoid follicles in the small intestine that play an essential role in immune surveillance and the generation of mucosal immunity. Research has shown that GMP can enhance the proliferation of lymphocytes within Peyer’s patches and stimulate the secretion of immunoglobulin A (IgA), which is vital for mucosal defense.

Some animal studies (such as those in mice) have found that oral administration of GMP increases IgA-secreting cell numbers in Peyer’s patches and promotes the production of anti-inflammatory cytokines. These effects are believed to arise from GMP’s ability to bind bacterial toxins, inhibit pathogen adhesion, and favorably modulate the gut microbiota, thereby indirectly supporting the immune function of Peyer’s patches. However, while there is meaningful preclinical evidence, robust human clinical data are limited. Thus, while the scientific rationale is promising and supported by experimental data, the evidence base is not yet strong enough for a top rating but is more than anecdotal or purely traditional.