Animals have similar responses to stress. Some nutritionists feel dogs may overeat simply because they are bored and there literally is not much else to do. Some dogs may not get into the garbage can because they are hungry but because they need something to do - the food they find is just a bonus. The competition for food, whether perceived or actual, makes some dogs much more focused on their food and can lead to obesity. Conversely, an inside dog uses relatively few calories to maintain normal body temperature.
Various medications can influence metabolism and appetite.
These include the glucocorticoids such as prednisone and dexamethasone, the barbiturates such as phenobarbital which is used to control epilepsy, and a class of drugs called benzodiazepines which includes valium. In the disease hypothyroidism , the dog's body produces less thyroid hormone. Thyroid hormone influences metabolic rate. Less thyroid hormone means lower metabolic rate and lower energy needs. A normal dog will become overweight if it develops hypothyroidism and is fed the same amount it was fed when it was healthy.