The present invention relates to methods of treating metabolic syndrome, Type 2 diabetes mellitus, atherogenic dyslipidemia and/or obesity. The present invention also relates to methods of restoring the incretin effect, to restoring physiologic control of glucagon levels, to restoring first-phase insulin secretion, and to restoring the physiologic glucose-dependent insulin secretion. The methods of the present invention comprise administration of a selective κ-receptor antagonist, such as guanidinylated naltrindole (GNTI), or pharmaceutically acceptable derivatives thereof to a subject in need thereof.