Weight Loss in Cats

Key Takeaways

Weight loss is a common symptom of a variety of conditions in cats. 

• Any illness, injury, or circumstance that reduces appetite, alters the metabolism, interferes with eating, or disrupts digestion and absorption of nutrients can lead to weight loss

• Associated symptoms may be obvious, such as vomiting or diarrhea, or a cat may appear otherwise well

• Weight loss can be circumstantial and improve with better nutrition or passing of the initial cause (e.g. stress)

• Chronic weight loss, lack of appetite, and inability to regain weight indicate a more serious underlying condition

• Unexplained weight loss always warrants further investigation and veterinary attention

• Typical diagnostics include a physical exam, blood work, urinalysis, fecal analysis, and diagnostic imaging

• Treatment is determined by the underlying cause and prognosis varies from mild and self-limiting to fatal even with aggressive treatment

A Closer Look: What is Weight Loss in Cats?

**Unexplained weight loss always warrants investigation and veterinary attention. **Weight loss is usually a gradual process, even when it happens quickly, so it rarely indicates an emergency. Many of the potential causes of weight loss are serious, so getting care as quickly as possible increases the likelihood of a good outcome. 

Weight loss accompanied by complete loss of appetite (anorexia) requires urgent veterinary care. Cats that do not eat for more than just a few days are at risk of potentially fatal hepatic lipidosis, especially if they are overweight or obese to start with. Sometimes healthy cats lose weight due to stress and changes in their surroundings. Conflict with other pets, changes in diet, travel or moving, and other stressors can lead to loss of appetite and weight loss. 

Weight loss over long periods may be subtle and difficult to detect for pet parents. Regular weight checks can track changes and allow earlier investigation. Senior cats, FIV-positive cats, kittens, and cats with chronic health conditions benefit from veterinary attention as soon as unexplained weight loss is noticed.

Possible Causes

Weight loss is a consequence of insufficient food intake or a dysfunction of food absorption, digestion, or metabolism. Some conditions may cause both decrease in appetite and absorption disorders.

Causes of insufficient intake include:

• Insufficient portions provided • Competition • Parasites (e.g. tapeworm) • Poor-quality or unsuitable food

Causes of lack of appetite include:

• Stress, pain, or injury • Infections • Toxins • Cancer

Causes of loss of nutrients include:

• Malabsorption/maldigestion syndromes • Persistent diarrhea • Persistent vomiting • Infection • Parasites

• Gastroenteritis • Inflammatory bowel disease • Exocrine pancreatic insufficiency • Diabetes mellitus

• Liver disease • Kidney disease

Causes of increased metabolism or energy demands include:

• Hyperthyroidism • Cancer • Pregnancy/Nursing

Causes of injury, physical disorder reducing food intake include:

• Jaw injury* • Masticatory myositis • Oral tumor • Megaesophagus

*It is rare for periodontal disease, dental tartar, decay, or dental abscesses to result in weight loss.

Risk Factors

The severity and rate of weight loss depends on the cause. Sudden weight loss may occur due to vomiting and diarrhea. Rapid weight loss may be circumstantial, due to stress or change in environment. More gradual weight loss may be caused by chronic conditions such as kidney or liver disease.   Cats with weight loss may show a normal, increased, or decreased appetite depending on the underlying condition. 

In some cases, weight loss is a sign that an underlying condition is worsening. Cachexia (weight loss and muscle wasting) is associated with chronic organ failure, cancer and other severe conditions.

Testing and Diagnosis

Tests to investigate weight loss include:

• Physical examination • Urinalysis • Fecal analysis • Parasite testing • Diagnostic imaging

• Bloodwork, including complete blood count, serum biochemistry, thyroid hormone levels

Treatment varies widely depending on the cause of the weight loss. Some cases of weight loss resolve on their own without treatment, while some are fatal even with early diagnosis and treatment.

Similar symptoms

Weight loss in association with dehydration: Dehydration is typically temporary and resolves when the cat’s hydration status returns to normal.

Associated Symptoms

• Lack of appetite (anorexia) • Increased appetite (polyphagia) • Increased urination (polyuria)

• Increased drinking (polydipsia) • Vomiting • Diarrhea • Lethargy • Hiding • Inappropriate elimination