Symptoms

My cat is losing weight but still eating. Why?

Updated 2026-07-16 · Not a substitute for professional veterinary care

Why eating well and still losing weight is a red flag

It sounds contradictory, and that is exactly why it matters. When a cat eats normally or even more than usual but keeps losing weight, the body is burning through fuel faster than food can replace it, or is not absorbing the nutrition. Two common causes do exactly this:

• Overactive thyroid (hyperthyroidism), the sped-up metabolism burns weight off despite a big appetite, often with increased thirst and restlessness.
• Diabetes, the body cannot use its sugar for energy, so it breaks down fat and muscle while the cat eats and drinks more.

Digestive disease and, in older cats, other serious conditions can also cause it.

Why it is so easy to miss

Cats lose weight gradually, and a cat that is eating happily does not look sick. Owners often notice only when the cat feels bonier on a stroke or a photo from months ago looks different. Weighing at home, or a simple monthly note, turns an invisible drift into something you can catch. A change of even a few percent of body weight is worth a vet's attention in a cat.

What to do

1. Book a vet visit. A basic blood test can check thyroid and blood sugar and usually gives a clear answer.
2. Bring any record of the weight change and when it started, plus notes on thirst, appetite, and energy.
3. Both thyroid disease and diabetes are very treatable when caught early.