Unexplained Weight Gain in Cats

Key Takeaways

Unexplained weight gain is an accumulation of excess body fat with a normal or decreased food intake. This is uncommon in cats. 

• Other symptoms may be present, and depend on the underlying medical condition associated with the unexplained weight gain

• Medical conditions that may result in unexplained weight gain include hypothyroidism and hyperadrenocorticism; both are rare in cats

• More commonly, weight gain in cats is explained (obesity), resulting from excessive food intake relative to caloric expenditure

• Some conditions cause an enlarged abdomen and falsely present as unexplained weight gain include, such as pregnancy, intestinal parasites, build up of abdominal fluid, enlarged abdominal organs, abdominal tumors, and a prominent primordial pouch

• Diagnostics to investigate include physical exam, blood tests, diagnostic imaging, urinalysis, and fecal analysis

A Closer Look: What is Unexplained Weight Gain in Cats?

In a healthy cat, body weight is expected to increase when the number of calories consumed is consistently higher than the number of calories expended. Unexplained weight gain is uncommon in cats. It can be difficult for pet parents to assess if weight gain in a cat is explicable or not. Some overweight cats are “picky eaters” as a result of being overfed. This can be incorrectly misinterpreted as poor appetite. 

Whether weight gain is explained or not, consultation with a veterinary professional to review nutritional guidelines and investigate if there is an underlying condition is the best course to optimize long term health outcomes.

Possible Causes

Conditions that are associated with unexplained weight gain include:

Hypothyroidism • Hyperadrenocorticism

Risk Factors

Unexplained weight gain is rare in cats. Overfeeding resulting in weight gain is common, and often leads to obesity, which is associated with many other serious health conditions including diabetes mellitus and osteoarthritis

In cases where weight gain is truly unexplained, the root cause may be a serious underlying condition and warrants further investigation. If weight gain is presumed to be due to overfeeding, it is also recommended to consult with a veterinary nutritionist or veterinarian before restricting a pet’s food intake.

Testing and Diagnosis

Diagnosis of underlying conditions associated with unexplained weight gain often includes:

• Physical exam • Blood and hormone level testing • Diagnostic imaging • Urinalysis • Fecal analysis

These tests are primarily performed to rule out other conditions that may appear as weight gain, but actually do not lead to the accumulation of excess body fat.

Similar symptoms

Other conditions that falsely present as unexplained weight gain include: 

• Pregnancy • Intestinal parasites • Ascites (build-up of abdominal fluid) • Enlarged abdominal organs (e.g. pyometra)

• Abdominal tumors • Prominent primordial pouch (a flap of excess skin near the lower abdomen found in all cats)

The most common cause of weight gain in cats is explained from excessive food intake (obesity).

Associated Symptoms

Conditions that result in unexplained weight gain may also be associated with: 

• Decreased appetite • Lethargy • Weakness • Skin and coat conditions • Muscle wasting • Increased thirst

• Increased urination

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