DPP4 and diabetes mellitus: The results obtained in this SR demonstrate the heterogeneity of the origin and amino acid composition of proteins and/or peptides, highlighting those of animal origin (fish and mollusks) and vegetable origin (green microalgae, tamarind seeds, and black beans), regarding their efficacy on various therapeutic targets (DPP-IV, AAM, RI, GLUT2, and SGLT1) of DM.