I have flavored coffee sometimes, and as long as I don’t add anything (except water sometimes to cool it off so I can drink it faster!) to it, I think the fasting time continues. ;)
But it depends on what you’re fasting for. If it’s for weight loss, you’re good. If it’s for bloodwork at the doctor’s, I got scolded last time I had black coffee before I went–in that instance you can only have water!
Technically, yes. For some it may not because it won’t spike their insulin but anything flavored can even if it’s zero cal. I always think back to when I used to chew gum 15 years ago and it always made me super hungry. It was zero calories but the flavors spiked my insulin.