Tessa, I'm sorry to hear of this with Fatcat. Rather than a diet change I want you to consider having him thoroughly examined by his vet inclduing diagnostics in the form of blood and urine tests. An "always hungry" elderly cat is either hyperthyroid, diabetic, or both. His frequent vomiting is more indicative of hyperthyroidism than diabetes. A simple T4 (total thyroid blood test) will identify hyperthyroidism which is then usually treated with methimazole either given orally or as a transdermal gel rubbed on his ear skin. A simple blood glucose test will identify diabetes.
Please respond with further questions or concerns if you wish.
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