Why Is My Cat Losing Weight?

Weight loss in cats is a more urgent finding than many owners realize. Because cats are small, even a 1-pound loss represents roughly 10% of a 10-pound cat's body weight — equivalent to a 150-pound human losing 15 pounds unintentionally. Unintentional weight loss always has a cause.

Hyperthyroidism is the #1 cause of weight loss in cats over 7-8 years old. The overactive thyroid gland revs up metabolism. Classic signs: weight loss despite a ravenous appetite, increased activity/restlessness, vomiting, diarrhea, and excessive thirst. It's treatable with medication, surgery, radioactive iodine, or dietary therapy.

Diabetes mellitus is another common cause, especially in overweight cats. Weight loss occurs because the body can't use glucose properly and breaks down muscle and fat instead. Signs include: weight loss, increased thirst, increased urination, and sometimes increased appetite.

Chronic kidney disease affects roughly 30% of cats over 10 years old. Early signs are subtle: slightly increased drinking, slight weight loss, and occasional vomiting. By the time weight loss is obvious, the disease may be advanced.

Intestinal disease (IBD or intestinal lymphoma) causes weight loss from malabsorption. GI lymphoma is actually one of the most common cancers in cats and can sometimes be managed long-term with treatment.

Dental disease can cause weight loss when it becomes too painful to eat, and cats are experts at hiding oral pain.