---
title: "Why Is My Cat Losing Weight UK?"
description: "UK guide — unintentional weight loss in cats is not normal ageing. Hyperthyroidism, kidney disease, diabetes, and when to book blood tests."
url: "https://pethealth.org.uk/health/why-is-my-cat-losing-weight-uk"
canonical: "https://pethealth.org.uk/health/why-is-my-cat-losing-weight-uk"
date_published: "2026-07-19"
date_modified: "2026-07-19"
source: "PETHEALTH+"
---

# Why Is My Cat Losing Weight UK?

**Unintentional weight loss in cats is not normal** — even if appetite seems unchanged. Common causes include **[hyperthyroidism](/glossary/hyperthyroidism), [diabetes](/glossary/diabetes-mellitus), [kidney disease](/glossary/chronic-kidney-disease), and cancer**. Senior cats over eight need prompt blood tests. Weigh regularly on kitchen scales.

## Weight loss vs deliberate dieting

Deliberate weight loss through a vet-recommended diet for [obesity](/health/cat-obesity-uk) 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

1. **Weigh your cat** on kitchen scales (weigh yourself holding the cat, then subtract your weight)
2. Note appetite, drinking, and behaviour changes
3. Book a vet appointment for **blood tests and urinalysis**
4. 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.

## FAQs

### 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.

## Sources

- [PDSA — Cat health advice](https://www.pdsa.org.uk/pet-help-and-advice/pet-health-hub)
- [Blue Cross — Cat advice](https://www.bluecross.org.uk/pet-advice)
- [International Cat Care — Weight loss](https://icatcare.org/advice/)
- [Cats Protection — Health advice](https://www.cats.org.uk/help-and-advice)

Canonical HTML: https://pethealth.org.uk/health/why-is-my-cat-losing-weight-uk
Last modified: 2026-07-19