Hi, I have a small bottle of coke zero a day as it helps me with that nasty taste in my mouth and helps my metabolism. My CDC as a few others I've met have all said its fine but it must be coke zero. It hasn't affected my weight loss. Good luck.
Diet coke and the decaf diet coke contains citric acid, this can cause you to come out of ketosis. Coke Zero and Dr Pepper Zero don't contain citric acid so are theoretically okay, but might make you feel hungry.... It's doesn't with me and I have a can or two a day but don't count them in my water consumption so they're extra.