Why is my cat losing weight?

Weight loss in cats is one of the most important symptoms to take seriously. Cats mask illness extraordinarily well, and by the time visible weight loss is apparent, a disease has often been progressing for weeks or months.

How to spot early weight loss

The best way to detect early weight loss is to feel your cat's spine, ribs, and hip bones weekly. You should be able to feel the ribs easily but not see them; the spine should feel smooth, not like a ridge of individual bones. A healthy adult cat's weight should remain stable; any progressive loss of more than 200–300 g per month warrants investigation.

The most common causes by age

In cats under 7 years:
- Hyperthyroidism is rare in younger cats but possible
- Diabetes mellitus — weight loss despite a good or ravenous appetite; increased thirst and urination
- Inflammatory bowel disease (IBD) — chronic intermittent vomiting, diarrhoea, and weight loss; managed with diet and medication
- Lymphoma — the most common cancer in cats; often responds well to treatment when caught early
- Intestinal parasites — less common in adult indoor cats but possible
- Dental pain — a cat with a broken tooth or severe gum disease eats less than owners realise

In cats over 8 years:
- Hyperthyroidism — the classic combination of ravenous appetite + weight loss in an older cat. See our dedicated article.
- Chronic kidney disease (CKD) — the single most common disease of older cats; weight loss is often the first visible sign
- Cancer — lymphoma, squamous cell carcinoma of the mouth, mammary tumours, and others
- Heart disease — cardiac cachexia causes progressive muscle wasting

Hepatic lipidosis — the cat-specific emergency

If a cat stops eating for 24–48 hours — for any reason — fat is mobilised to the liver faster than it can be processed, causing a life-threatening condition called hepatic lipidosis (fatty liver disease). This means that regardless of the underlying cause, any cat that has significantly reduced food intake needs prompt veterinary attention. Never put an overweight cat on an abrupt crash diet.

What to expect at the vet

Blood panel, urinalysis, thyroid level (T4), abdominal ultrasound. These tests together identify the vast majority of weight loss causes in cats.