Abstract: The present invention relates to compositions and methods for regulating body weight, and for treating conditions associated with obesity, particularly, obesity-related diabetes. The present invention is premised on the discovery that body weight can be effectively regulated by modulating the levels and/or activities of two gut hormones, PYY and ghrelin.

Abstract: The invention comprises an animal having a presurgical substantially normal gastrointestinal tract, which gastrointestinal tract has been surgically modified such that postsurgically there is a reduction of the volume of the stomach of the gastrointestinal tract, a reduction in the digestive area of the gastrointestinal tract, a reduction in the co-mingling of food with gastric, biliary and pancreatic juices, a reduction in the presurgical gastric output of the peptide ghrelin, a reduction in the threshold for satiety, a permanent reduction in presurgical weight, and an induction of a condition of malabsorption. The surgically-altered animal may be adapted for use as an animal model in a method wherein the biological mechanisms underlying obesity and its reduction may be investigated; and, in which the molecular biological effects of surgical intervention for obesity may be investigated; and, in which the efficacy of noninvasive alternatives to surgical intervention for obesity may be investigated.