Oral co-administration of 400 mg/kg L-serine and 2 g/kg glucose to mice drives an altered insulin response in STZ-treated mice (T1DM model) and BKS-db/db mice (T2DM model) versus healthy animals, with a decreased area under the curve (AUC) of L-serine and an increased AUC of glucose in mice with DM. The gene discussed is INS; the disease is type 2 diabetes mellitus.