Crucially, some oligopeptides with short sequences of 2–20 amino acids can be absorbed by the intestine into the blood circulation and exert systemic or local physiological anti-diabetic activities, such as decreasing blood glucose levels, improving glucose and insulin sensitivity in target tissues, and inhibiting key enzymes like α-amylase, α-glucosidase, and DPP-4 related to T2D [4,89,90]. The gene discussed is DPP4; the disease is type 2 diabetes mellitus.