Truly unexplained weight gain in dogs is uncommon, as most cases of weight gain that appear unexplained are linked to overfeeding in dogs. Unexplained weight gain is characterized specifically as weight gain occurring despite reduction of calorie intake and reduction of appetite. Genuine unexplained weight gain is a symptom of two major diseases that require prompt medical intervention.
Hypothyroidism results in decreased metabolism. Cushing’s disease disrupts hormone production.
The two possible causes of unexplained weight gain in dogs, hypothyroidism and Cushing’s disease, are both common in dogs and have their own specific risk factors and predilections.
A physical examination and comparison of current weight to a previously documented weight confirms weight gain. If overfeeding has been ruled out through assessment of feeding practices, a number of tests are used to identify the underlying cause:
Once the cause is identified, treatment depends on the specific disorder. For Cushing’s disease, medication, surgery, or radiation are used. In cases of hypothyroidism, medication to increase or replace the absent hormones are given as a life-long treatment.
It may appear a pet is refusing food and still gaining weight in cases where the pet is already overfed. This situation appears similar to unexplained weight gain, but is not related as the weight gain is due to high caloric intake.
Spaying or neutering a pet often results in weight gain, by altering hormone production and making it easier for the pet to put on weight. Castration in and of itself does not cause weight gain; the surgery merely reduces the calorie requirement of the pet. This scenario is not a cause of unexplained weight gain.