Incretins are metabolic hormones released after a meal that increase insulin secretion from pancreatic β-cells. The two main incretins are the intestinal peptides glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. Both induce a decrease in glycemia, slow down the absorption of nutrients, and are inactivated by the enzyme dipeptidyl peptidase-4. Recently, incretin-based therapies have become a useful tool to treat diabetic patients, and different studies have focused on the identification of glucagon-like peptide-1 receptor agonists, including those of natural origin. This review focuses on the new findings of medicinal plants and natural products as possible active agents on the potentiation of incretin receptor signaling. Among these, soluble fiber from species of Plantago and guar gum show promising effects, iridoid derivatives are relevant activators of incretin receptors, and derivatives of cyanidin, especially diglycosylated ones, are an interesting source of dipeptidyl peptidase-4 inhibitors.