How old is your cat? Does he have any mouth ulcers? Any teeth that need removing? I'm concerned that his appetite is affected by his dental health, because it could mean he has something like Stomatitis, which is an auto-immue disease resulting in chronic, painful mouth inflammation. Can be very difficult to treat, and something like Plaque Attack is not likely to make any difference whatsoever. Even if Stomatitis isn't the issue, I'd stay away from Plaque Attack. Not only does it contain ingredients cats shouldn't be ingesting, but good luck to anyone that actually tries to spray this stuff in their mouth!