Is that all he was eating.........nothing else?

How old is your dog? Canned chicken has a HUGE amount of sodium in it, this can negatively impact a dogs health over a long period of time, your dog isn't getting all the vitamins and nutrients of a balanced diet dogs are omnivores, eating almost anything, stop feeding your dog canned chicken, if you dog is experiencing kidney failure, you need to stick to a low protein diet, which your dog might hate. More veggies, some meat without all the sodium