CCK and Obesity: The objectives of this study were to determine that: (1) diet–induced obesity (DIO) and diet-induced obesity resistance (DR) rats were induced by high fat diet (HFD); (2) the changes of gastrointestinal motility were measured in DIO and DR groups; (3) the changes of serum gastrointestinal hormones such as cholecystokinin (CCK), motillin and gastrin were examined in DIO and DR groups; and (4) the possible mechanism of a regulating gastrointestinal motility was related to the cells and neurons in the GI tract.