Polyphagia (increased hunger) at Toots's age is usually associated with either diabetes mellitus or hyperthyroidism. The great majority of diabetics increase their water intake and urine output while just 35% of hyperthyroid cats do so. In either case, I expect weight loss instead of gain but I do see ~10% of hyperthyroid cats gain instead of lose weight. Toots's vet will want to perform a thorough physical exam including diagnostics in the form of blood and urine tests. A simple blood glucose should identify diabetes while a T4 and fT4 (total thyroid and free thyroid blood test) should identify hyperthyroidism.
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