Why Is My Senior Cat Losing Weight?

Unexplained weight loss in a senior cat (10+ years) is one of the most important clinical signs to act on. Unlike dogs who show illness through behavior changes, cats are masters of concealment — weight loss may be the ONLY visible sign of serious disease for months.

Hyperthyroidism is the #1 cause of weight loss in cats over 8 years old. The overactive thyroid gland ramps up metabolism, causing: weight loss despite a normal or increased appetite, increased thirst and urination, hyperactivity or restlessness, vomiting, unkempt coat, and sometimes behavioral changes (increased vocalization, aggression). It's very treatable with medication, radioactive iodine, dietary management, or surgery.

Chronic kidney disease (CKD) is the #2 cause, affecting up to 30% of cats over 15. It causes gradual weight loss, increased thirst and urination, decreased appetite, vomiting, bad breath, and poor coat quality. Early detection through regular blood work allows management that significantly extends quality of life.

Diabetes mellitus causes weight loss with increased appetite (the body can't use glucose for energy, so it breaks down fat and muscle). Other signs: increased thirst and urination, and a plantigrade stance (walking flat on the hocks instead of on the toes). Some cats achieve remission with early, aggressive treatment.

Cancer is responsible for weight loss in a significant proportion of senior cats. Lymphoma (especially intestinal lymphoma) is the most common feline cancer and causes gradual weight loss, decreased appetite, vomiting, and diarrhea.

Dental disease can make eating painful, causing gradual weight loss. Signs include drooling, dropping food, and preference for soft foods.

Inflammatory bowel disease (IBD) causes malabsorption — the cat eats but can't absorb nutrients properly. It often coexists with or progresses to intestinal lymphoma.