Cat Health
Why Is My Cat Losing Weight UK?
Published Last updated 2 min read
Quick answer
Unintentional weight loss in cats is not normal — even if appetite seems unchanged. Common causes include hyperthyroidism, diabetes, kidney disease, and cancer. Senior cats over eight need prompt blood tests. Weigh regularly on kitchen scales.
Key takeaways
- No — investigate rather than accept loss as ageing. Senior cats commonly have treatable conditions such as hyperthyroidism or kidney disease that cause weight loss.
- Hyperthyroidism, diabetes, and intestinal disease can cause weight loss despite a good or increased appetite. Blood tests are needed to identify the cause.
- Heavy parasite burdens can contribute, especially in kittens or cats not on regular worming. Faecal testing and appropriate worming help identify this.
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Weight loss vs deliberate dieting
Deliberate weight loss through a vet-recommended diet for obesity is different from unexplained loss — ribs and spine becoming more visible without trying to slim your cat.
Concerning signs:
- Spine and hip bones more prominent
- Drop on kitchen scales over weeks
- Loss despite normal or increased appetite
- Dull coat or behaviour change
Common causes in UK cats
| Condition | Typical signs |
|---|---|
| Hyperthyroidism | Weight loss, increased appetite, hyperactivity |
| Kidney disease | Weight loss, increased drinking, reduced appetite |
| Diabetes | Weight loss, increased appetite and thirst |
| Dental disease | Reluctance to eat hard food, bad breath |
| Intestinal disease | Diarrhoea, vomiting, poor coat |
| Cancer | Progressive loss, often in senior cats |
What to do
- Weigh your cat on kitchen scales (weigh yourself holding the cat, then subtract your weight)
- Note appetite, drinking, and behaviour changes
- Book a vet appointment for blood tests and urinalysis
- Do not delay — many causes are treatable when caught early
When to call your vet
Contact your vet promptly for any unintentional weight loss. Same-day care if your cat is not eating, vomiting repeatedly, or seems weak.
Sources & further reading
Facts in this guide are rewritten in plain English from publicly available UK advice. We name the organisation where a specific point comes from their guidance. Links below go to the original pages — use them to read the source material directly.
PETHEALTH+ is independent. These organisations do not sponsor, approve, or partner with this website. Guidance checked against sources listed below (last updated 2026-07-19).
- Cat Obesity UK
- Unexplained Weight Loss in Cats
- Why Is My Cat Not Eating UK?
- Hyperthyroidism in Cats
- Can I Give My Cat Antihistamines? UK Guide
- Can Cats Eat Bread UK?
- Can Cats Eat Cheese UK?
- Can Cats Eat Ice Cubes UK?
Also see symptoms, symptom checker, and poison guide.
Frequently Asked Questions
- Is weight loss normal in old cats?
- No — investigate rather than accept loss as ageing. Senior cats commonly have treatable conditions such as hyperthyroidism or kidney disease that cause weight loss.
- Why is my cat losing weight but still eating?
- Hyperthyroidism, diabetes, and intestinal disease can cause weight loss despite a good or increased appetite. Blood tests are needed to identify the cause.
- Do worms cause weight loss in cats?
- Heavy parasite burdens can contribute, especially in kittens or cats not on regular worming. Faecal testing and appropriate worming help identify this.
- How much weight loss is concerning?
- Any noticeable unintentional loss matters — prominent spine and ribs, or a drop on kitchen scales. Weigh monthly to catch small changes early.