Does coffee affect fasting?

Whether you follow an eating protocol like time restricted eating or intermittent fasting, ingestion of calories at the wrong time can throw your routine out of whack. The main idea behind both modes of eating is that there is a certain window in which you eat and a fasting window in which you don’t. Obviously, consuming water during your fasting period is fine, however, is this the same for coffee? Should coffee just be black? Are you allowed certain milks? If so, how much? Let’s talk into this a little more.