Unexplained Weight Gain in Dogs

Published on
Last updated on
3 min read

Key takeaways

Unexplained weight gain is specifically characterized by the occurrence of weight gain in spite of a reduction in calories and appetite.

  • Unexplained weight gain in dogs is uncommon, as many causes of weight gain have an explanation that has not yet been identified
  • For example, pregnancy, tumor development, or bloat may give the appearance of unexplained weight gain
  • In some cases, weight gain is caused by overfeeding and lack of physical activity
  • True unexplained weight gain is most often a symptom of hypothyroidism or Cushing’s disease, which require lifelong medication, surgery, and/or lifestyle management
  • These conditions can be diagnosed through blood work, medical imaging, and urinalysis
  • Treatment and prognosis depend on underlying condition
Are you concerned?

Connect with a vet to get more information about your pet’s health.

Book an online vet

A closer look: Unexplained Weight Gain in Dogs

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.

Connect with a vet to get more information

With DVM, ICH certifications and great reviews by pet parents like you for this symptom

Possible causes

Hypothyroidism results in decreased metabolism. Cushing’s disease disrupts hormone production.

Risk factors

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.

Testing and diagnosis

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:

  • Urinalysis
  • Blood work
  • Imaging (X ray, MRI, ultrasound)
  • Hormone level testing

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.

Similar symptoms

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.

Associated symptoms


No Author - Writing for Hill's Pet Nutrition
PetMD Editorial - Writing for PetMD
American Veterinarian Staff - Writing for dvm360®
Mark E. Peterson , DVM, DACVIM-SAIM/ Janice E. Kritchevsky , VMD, DACVIM-LAIM - Writing for Merck Veterinary Manual
Deborah S. Greco, DVM, PhD, DACVIM-SAIM - Writing for Merck Veterinary Manual

Our editorial committee

Our medical review team is responsible for validating and maintaining the quality of our medical information.