Additionally, postbiotics like muramyl dipeptide, derived from bacterial cell walls, alleviate obesity-induced insulin resistance by targeting nucleotide-binding oligomerization domain 2 (NOD2) and interferon regulatory factor 4 (IRF4), while interactions between muropeptide and NOD2 may improve insulin sensitization and alleviate inflammation [181,182]. Here, IRF4 is linked to obesity due to melanocortin 4 receptor deficiency.