Unexplained Weight Gain in Dogs

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

A Closer Look: What is 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.

Possible Causes

Unexplained weight gain in dogs is caused by either hypothyroidism, which results in decreased metabolism, or Cushing’s disease, which 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. Untreated or unceasing weight gain in dogs can lead to obesity, which carries a number of serious risk factors, including osteoarthritis and diabetes mellitus, which can be life threatening.

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 dog is gaining weight 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. 

Other symptoms that may cause weight gain without a decrease in caloric intake include:

• Increased appetite • Pregnancy • Intestinal bloat • Intestinal parasites • Fluid buildup in the abdomen (ascites)

• Pyometra • Large abdominal masses/tumors

Associated Symptoms

• Increased thirst • Increased urination • Uncontrolled overeating (polyphagia) • Heat intolerance • Lethargy

• Abdominal enlargement • Muscle weakness • Mental dullness • Changes in skin/coat