Flavonoids are a diverse family of plant polyphenolic substances that are derived from a combination of metabolites synthesized from phenylalanine and acetic acid. These molecules are best known for their beneficial effects as antioxidants and anticancer agents, but in a number of studies flavonoids have also been shown to alter insulin regulation. We present the metabolic engineering of the industrially important microorganisms Escherichia coli and Saccharomyces cerevisiae for flavonoid biosynthesis from the inexpensive phenylpropanoic precursors and glucose. Implantation of artificial flavonoid biosynthetic pathways through simultaneous episomal expression of plant-derived genes resulted in the biosynthesis of a library of flavonoid molecules, which includes flavanones, flavones, flavonols, flavanols, and anthocyanins. Further pathway optimization was achieved by increasing the intracellular pool of malonyl-CoA through episomal overexpression of the malonyl-CoA synthetase operon, acetyl-CoA carboxylase, biotin ligase and acetyl-CoA synthetase. By applying a mutasynthesis approach, various flavonoid analogues were produced from the recombinant strains. We further present the insulinotropic properties for various flavonoids, focusing primarily on unnatural green tea catechins. The effects of these compounds on glucose-stimulated insulin secretion and insulin biosynthesis in pancreatic beta-cells will be discussed.