My Cat Is Losing Weight but Still Eating: When Should I See a Vet?

Why is my cat losing weight but still eating?

Several conditions can produce similar signs. These are possibilities your vet may consider, rather than diagnoses that can be made from appetite alone.

An overactive thyroid: hyperthyroidism

Hyperthyroidism is an important cause of weight loss in older cats. Excess thyroid hormone speeds up the body’s metabolism, so a cat may become thinner even while eating enthusiastically.

Other signs can include increased thirst, restlessness, more vocalisation, vomiting or an untidy coat. Blood testing usually includes measurement of the thyroid hormone T4. Occasionally, repeat or additional testing is needed when the first result does not explain the clinical signs.

Diabetes mellitus

A cat with diabetes may lose weight despite a good or increased appetite because its body cannot use glucose effectively. Owners may also notice more drinking, larger clumps of urine in the litter tray or a change in strength and mobility.

Blood and urine tests help investigate these signs; appetite and thirst alone cannot confirm diabetes.

Intestinal disease

Conditions affecting the intestines can interfere with digestion and nutrient absorption. Some cats develop vomiting or diarrhoea, while others show more subtle changes.

Chronic intestinal inflammation and intestinal lymphoma can have overlapping signs. Further tests—and sometimes tissue samples—may be needed to distinguish them. Weight loss does not automatically mean cancer.

Chronic kidney disease

Kidney disease can cause weight loss, increased thirst and changes in urination. Appetite may become reduced or variable, although owners do not always recognise the change immediately.

Blood tests and urinalysis are interpreted together to assess kidney function. Blood pressure measurement and further investigations may also be appropriate.

Eating less than it appears

Visiting the food bowl is not always the same as eating enough. In a household with several cats, it can be difficult to know which cat finishes each meal.

Dental discomfort, stress, competition for food or a change in diet may reduce actual intake. Your vet will therefore ask about the food offered, the amount eaten and how your cat behaves during meals.

Is weight loss normal in older cats?

Age can influence muscle condition and nutritional needs, but noticeable weight loss should trigger a check rather than an assumption that your cat is “just getting old”.

Your vet can compare previous weights and assess both body fat and muscle. This matters because a cat may lose muscle around the spine or hindquarters while still carrying fat elsewhere.

For perspective, a change from 5 kg to 4.5 kg represents a 10% loss of body weight. You do not need to wait for that amount of loss before seeking advice: a smaller, persistent downward trend also deserves attention.

What should I record before the appointment?

A few observations can make the consultation more useful:

• Previous weights and when you first noticed a change
• The exact food, quantities offered and leftovers
• Whether appetite is normal, increased, reduced or variable
• Changes in drinking and litter-tray use
• Vomiting, diarrhoea or changes in stool appearance
• Activity, grooming, hiding, vocalisation or difficulty eating
• Medication, supplements and parasite prevention

If practical, feed cats separately for a short period so you can observe individual intake. Bring food packaging or photographs of the labels.

What tests might my vet recommend?

The investigation begins with the history and a physical examination. Your vet may check the mouth, thyroid region, heart, abdomen, hydration, body condition and muscle condition.

Initial tests may include blood tests, a thyroid hormone measurement and urinalysis. Further tests are selected according to the findings—for example, faecal testing, vitamin B12 measurement or abdominal imaging.

Your cat does not necessarily need every test. The aim is to build a clear explanation of the weight loss and choose investigations that can guide treatment.

What if the first blood tests are normal?

Normal initial results are useful, but they do not explain continuing weight loss on their own.

Your vet may recommend reviewing the weight trend, measuring actual food intake, repeating selected tests or investigating the digestive tract. The next step depends on what was tested, the examination findings and whether the weight loss is continuing.

Abdominal ultrasound can be useful in selected cats with unexplained weight loss.