It discloses a transformant for weight loss and lipid reduction, which is obtained by recombining and substituting human oxyntomodulin gene into thymidylate synthase gene of L.lactis genome. Wherein the recombinant substitution is homologous recombination by artificially synthesizing gene sequences, making the sequence flanking the human oxyntomodulin gene derived from the homologous sequences of thymidylate synthase gene in the L.lactis genome, then the gene fragments are electroporated into L. lactis, to carry out homologous recombination.