Why Is My Cat Losing Weight? Common Causes & What to Do

Weight loss in cats is one of the most important warning signs you can notice at home — and one of the easiest to miss, especially in long-haired cats. By the time weight loss is visible to the eye, it’s often been happening for weeks. Regular weighing is the best early warning system.

How to Tell If Your Cat Has Lost Weight

Run your hands along your cat’s spine and ribcage. You should be able to feel individual ribs with light pressure but not see them prominently. If ribs are very easy to feel and the spine feels sharp and bony, your cat has likely lost condition. Weigh monthly — even a loss of 200–300g in a small cat is significant.

Hyperthyroidism

The most common cause of weight loss in cats over 8 years old. The thyroid gland produces too much hormone, speeding up metabolism. Characteristic signs: weight loss despite a good or increased appetite, hyperactivity, vomiting, poor coat, increased thirst, and sometimes a palpable lump in the neck. Highly treatable with medication, radioactive iodine, or diet.

Diabetes

Weight loss despite a good appetite, combined with increased thirst and urination, is the classic presentation. Some cats also develop weakness in the hind legs — a plantigrade stance where they walk on their hocks. Managed with insulin injections and low-carbohydrate wet food. Many cats achieve remission with tight glucose control.

Kidney Disease

Affects 30–40% of cats over 12. Early signs are subtle — gradual weight loss, slightly increased thirst, reduced appetite. Later: vomiting, lethargy, very poor coat. Managed (not cured) with prescription renal diet, phosphate binders, fluid support, and anti-nausea medication. Early detection through regular bloodwork is critical.

Inflammatory Bowel Disease (IBD)

Chronic inflammation of the gastrointestinal tract causing poor nutrient absorption. Signs: weight loss, chronic vomiting and/or diarrhea, poor coat. Managed with dietary changes (hydrolyzed or novel protein diet) and often steroid medication.

Dental Pain

A cat with significant dental disease may eat less because chewing hurts. Look for: dropping food, head tilting while eating, drooling, bad breath, or sudden preference for soft food over dry.

Weight loss in cats is almost never normal and almost always treatable — especially when caught early. Monthly weigh-ins and twice-yearly vet checks for cats over 8 are the most powerful tools you have.