My cat is losing weight — what could be causing it?

Unintentional weight loss in cats is always a reason to investigate. Cats can lose weight gradually while still appearing active and eating, so regular weigh-ins are important — especially for cats over 7 years old.

Why weight loss matters

A cat that loses more than 10% of its body weight (less than 500g in a 5kg cat) in a short period has a significant medical problem until proven otherwise. Because cats' coats can mask body condition changes, use your hands to feel the spine and ribs — you should be able to feel them with slight pressure but not see them prominently.

Common causes of weight loss in cats

- Hyperthyroidism – The leading cause of weight loss in cats over 10 years old. The thyroid gland produces too much hormone, dramatically increasing metabolism. Despite a ravenous appetite, the cat loses weight rapidly. Other signs include hyperactivity, vomiting, increased thirst, and unkempt coat.
- Chronic kidney disease (CKD) – Very common in older cats. Reduced kidney function leads to nausea, reduced appetite, and muscle wasting.
- Diabetes mellitus – Insufficient insulin causes cells to starve despite adequate food intake. Signs include increased thirst, frequent urination, and weakness in the hind legs (diabetic neuropathy).
- Inflammatory bowel disease (IBD) – Chronic intestinal inflammation impairs nutrient absorption.
- Dental disease – Pain from periodontal disease, tooth resorption, or mouth ulcers can cause a cat to eat less, especially hard food.
- Cancer – Lymphoma is particularly common in cats and can cause weight loss, vomiting, and diarrhoea.

Track your cat's weight

Use Flovvi to log your cat's weight monthly. Spotting a trend early allows for earlier diagnosis and better outcomes.