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.
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.