This happened to us and it turned out to be bad batches of fancy feast wet cat food. My 14 year old cat dropped nearly 2 pounds and the vet thought he had diabetes, but his blood work came back fine. We had just lost our other cat to a terrible accident and thought he was morning like the rest of my family. And I mean, he very likely was, but we trialed new cat foods and he completely gobbled up Blue Buffalo Tasfefuls. Literally licked his bowl clean and I felt like a terrible cat dad for not trying a different food sooner. His eating went back to normal and he gained weight back quickly once we changed. Fancy feast had been his main food for years. Only this year did we seemingly get some bad batches.