It wouldn’t break mine. The flavoring is an oil that they chemically soak into lesser quality beans, but you don’t get (particularly) any more calories per cup than you would from regular straight black coffee.
The purest purist will tell you to avoid it, and it’s a thing you can maybe cut down on later if you’re looking to eliminate things that might be holding you up, but for now, if it helps you not eat, that’s a winner.