Why Is My Cat Losing Weight? Causes and Next Steps
Updated 2 August 2026 · Reviewed against PDSA and Cats Protection veterinary guidance
Unplanned weight loss is not a normal part of ageing. It can be hard to notice under a thick coat, and by the time the spine or hips look prominent a cat may have lost both fat and muscle. PDSA advises contacting your vet whenever you think your cat has lost weight.
The most useful clue is whether appetite has increased, decreased or stayed the same, but no pattern identifies a disease by itself. A veterinary examination and, often, blood and urine tests are needed to find the cause.
The short answer
Book a veterinary appointment for any unexplained weight loss. Weigh your cat consistently, note appetite, thirst, urination, vomiting, diarrhoea and behaviour, and take those records with you. Do not simply add high-calorie food until disease has been considered because the appropriate diet depends on the diagnosis.
Call a vet promptly if
- Weight loss is rapid, your cat is weak, collapses, seems confused or has difficulty breathing.
- Your cat is vomiting repeatedly, cannot keep water down or has severe diarrhoea.
- Your cat has stopped eating or has eaten nothing for 24 hours.
- There is marked thirst or urination with lethargy, dehydration or sudden deterioration.
- The gums or whites of the eyes look yellow, very pale or blue-grey.
Common reasons cats lose weight
PDSA lists worms, dental disease, hyperthyroidism, stress, insufficient food, kidney disease and diabetes among recognised causes. Liver disease, pancreatitis, cancer, inflammatory bowel disease and viral infections are other possibilities. More than one problem can be present in an older cat.
Access to food matters too. In a multi-cat home one cat may block another from the bowl, while an outdoor cat may be eating elsewhere or exercising more. Those explanations should be checked, but they should not be used to dismiss a measurable downward trend.
Losing weight while eating more
Weight loss despite a strong or increased appetite is a classic reason vets consider hyperthyroidism and diabetes. Hyperthyroid cats may also be restless, vocal, thirsty, have a fast heart rate or an unkempt coat. Cats with diabetes often drink and urinate more and may become weak in the back legs.
Poor nutrient absorption, parasites and some intestinal diseases can also cause this pattern. Appetite alone cannot separate them, and normal eating does not make weight loss safe to watch indefinitely.
Losing weight with a reduced appetite
Dental pain, nausea, kidney disease, pancreatitis, liver disease, infection, cancer and stress can all reduce food intake. Look for drooling, bad breath, food dropping, lip licking, hiding, vomiting or a change in drinking, but remember that cats often hide discomfort.
A cat that stops eating is at risk of serious complications, including hepatic lipidosis, particularly if overweight. Contact your vet if no food has been eaten for 24 hours, and sooner for kittens, frail cats or a cat with other symptoms.
How to confirm a real weight change
Use the same digital scales, at roughly the same time of day, and record the result rather than relying on memory. If the cat will not stand on scales, weigh yourself holding the cat and subtract your own weight; a veterinary scale is more accurate for small changes.
Combine weight with body condition and muscle condition. At an ideal body condition the ribs can be felt under a light fat covering and there is a visible waist. Muscle loss is often first noticed over the spine, shoulder blades and back legs. Photographs from above and the side can reveal gradual change hidden by fur.
What your vet may check
Your vet will review the weight trend, diet, appetite, drinking, urination, stools, vomiting, medication and access outdoors. The examination commonly includes the mouth and teeth, thyroid area, heart, abdomen, hydration, body condition and muscle condition.
Blood and urine tests can assess kidney and liver function, glucose, blood cells and thyroid hormone. Depending on the findings, the next step may include blood pressure, faecal testing, imaging or a structured diet trial. Treatment and nutrition should target the diagnosed cause.
Supporting your cat before the appointment
Continue a familiar complete diet unless your vet advises otherwise, make food and water easy to reach, and feed cats separately so intake can be measured. Record exactly how much is offered and left, rather than describing appetite as simply good or bad.
Do not start supplements, appetite stimulants or a major diet change without advice. Some diseases require specific nutrient levels, and a sudden change can obscure the history or cause digestive upset.
Frequently asked questions
Why is my cat skinny but always hungry?
Hyperthyroidism, diabetes, parasites and poor nutrient absorption are possible causes. This pattern needs a veterinary appointment and usually blood and urine tests rather than simply feeding more.
Is weight loss normal in an old cat?
No. Older cats may lose muscle, but that change can reflect pain or disease and should not be dismissed as ageing. Cats Protection recommends regular weight monitoring and veterinary checks for senior cats.
How much weight loss is concerning in a cat?
There is no single safe threshold for every cat. A consistent unexplained downward trend, visible loss of muscle or a change accompanied by other symptoms warrants veterinary advice.
Should I feed my underweight cat more?
Only after discussing the cause with your vet. Extra calories may be appropriate, but kidney, intestinal, dental and endocrine diseases need different management.
How often should I weigh my cat?
Monthly checks are useful for a stable adult and more frequent monitoring may be advised for a senior cat or one under treatment. Use the same method and record every result.
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References
This guide is for general information only and is not a substitute for veterinary advice. If you are worried about your cat, contact your vet.