Abstract Glucose-dependent insulinotropic polypeptide (GIP) and peptide YY (PYY) are secreted from the intestinal K- and L-cells, respectively, following a meal. Both peptides are believed to play a key role in glucose homeostasis and energy expenditure. This study investigated the effects of daily administration of the stable and specific GIP-R antagonist, (Pro 3)GIP (25 nmol/kg) and the endogenous truncated form of PYY, PYY(3-36) (50 nmol/kg), in mice fed with a high fat diet. Daily i.p. injection of (Pro 3)GIP, PYY(3-36) or combined peptide administration over 24 days significantly ( P < 0.05–0.01) decreased body weight compared with saline-treated controls without change in food intake. Plasma glucose levels and glucose tolerance were significantly ( P < 0.05) lowered by (Pro 3)GIP treatment alone, and in combination with PYY(3-36). These changes were accompanied by a slight improvement of insulin sensitivity in all of the treatment groups. (Pro 3)GIP treatment significantly reduced plasma corticosterone ( P < 0.05), while combined administration with PYY(3-36) significantly lowered serum glucagon ( P < 0.05). No appreciable changes were observed in either circulating or glucose-stimulated insulin secretion in all treatment groups. (Pro 3)GIP-treated mice had significantly ( P < 0.01) lowered fasting glucose levels and an improved ( P < 0.05) glycemic response to feeding. These comparative data indicate that chemical ablation of GIP receptor action using (Pro 3)GIP provides an especially effective means of countering obesity and related abnormalities induced by consumption of high fat energy rich diet.