Methods for treating type two diabetes mellitus in a subject in need thereof and pharmaceutical compositions for the treatment of type two diabetes mellitus are disclosed, wherein the methods and compositions of the invention are based on the use of non-glycosylated apolipoprotein A-IV produced by a protein expression system, such as a bacterial expression system. Also disclosed are methods for substantially restoring glucose tolerance in a subject in need thereof to a normal level and methods for lowering blood glucose levels in a subject in need thereof based on administering non-glycosylated apolipoprotein A-IV produced by a protein expression system.