Cat Losing Weight But Still Eating? 7 Causes & When to Worry

A cat that's eating normally but losing weight is a classic red flag in veterinary medicine. This specific pattern — good appetite + weight loss — narrows down the possibilities considerably. Here are the most likely causes.

Hyperthyroidism — The #1 Cause in Senior Cats

The thyroid gland overproduces thyroid hormone, revving up metabolism. The cat eats voraciously — sometimes stealing food — but keeps losing weight. Other signs: increased thirst and urination, vomiting, diarrhea, hyperactivity, vocalization (especially at night), rapid heart rate, and poor coat quality. Most common in cats over 10. Treatment is highly effective: radioactive iodine (curative, one-time treatment), daily methimazole medication, or iodine-restricted diet.

Diabetes Mellitus

The body can't use glucose properly. Sugar spills into the urine, dragging water with it. The cat literally pees out calories. Signs: increased thirst and urination, weight loss despite good appetite, plantigrade stance (walking on hocks), lethargy, poor coat. Unlike in dogs, diabetic remission IS possible in cats with early aggressive management — low-carb diet + insulin.

Chronic Kidney Disease

The #1 cause in older cats overall. Failing kidneys can't concentrate urine, so the cat drinks and urinates excessively. Uremic toxins cause nausea and appetite loss. However, some CKD cats maintain appetite while losing muscle mass. Weight loss is often the first sign, before blood work changes.

Inflammatory Bowel Disease (IBD)

Chronic inflammation of the intestinal tract prevents proper nutrient absorption. The cat eats but can't extract the calories. Often accompanied by vomiting, diarrhea, or both. Diagnosis requires intestinal biopsy. Management: diet change (novel protein or hydrolyzed), steroids, vitamin B12 injections.

Exocrine Pancreatic Insufficiency (EPI)

The pancreas doesn't produce enough digestive enzymes. Food passes through undigested. The cat eats ravenously but loses weight. Stool is often pale, greasy, and voluminous. Diagnosis: serum TLI test. Treatment: enzyme replacement with every meal.

Cancer

Intestinal lymphoma is one of the most common cancers in cats. Weight loss is often the first and only sign for months. Any unexplained weight loss in an older cat warrants imaging (ultrasound).

Dental Disease

Severe dental pain makes eating difficult. The cat approaches food eagerly but drops it or chews awkwardly. They may prefer soft food over kibble. Often accompanies other diseases.

When to See a Vet

Any unexplained weight loss is a reason for a vet visit. Blood work (CBC, chemistry, T4) and urinalysis are the minimum workup. Ultrasound if IBD or cancer is suspected.