Search terms included flavan-3-ol, flavanol, catechin, epicatechin, epigallocatechin, gallocatechin, procyanidin, theaflavin, γ-valerolactone, valeric acid, 3,4-dihydroxyphenyl propionic acid, 3-hydroxyphenyl propionic acid, 3-hydroxyphenylacetic acid, 3,4-dihydoxyphenylacetic acid, homovanillic acid, protocatechuic acid, 3-hydroxybenzoic acid, green tea, grape seed extract, cacao, diabetes, glucose, insulin, insulin resistance, beta cell, pancreas, glucagon, incretin effect, and vasodilation. This evidence concerns the gene GCG and diabetes mellitus.