These observations indicate that the chronic suppression of postprandial blood glucose elevation, which is induced by the consecutive ingestion of Guava Leaf Tea containing GvEx via its alpha-glucosidase inhibition, plays an important role in the improvement of not only hyperglycemia and diabetes symptoms, as similarly induced by typical alpha-GIs, but also insulin resistance in pre-diabetic and diabetic patients. The gene discussed is GAA; the disease is diabetes mellitus.