Unless you induce diarrhea, there’s food residues in the gut which keep adding to your energy bottomline for up to a few days. It’s unlikely that having a coffee or a supplement has a noticeable impact on your fasted state during intermittent fasting (when fasting 3+ days, things are different). To be sure, one could just measure serum insulin and ketone levels. Coffee will raise blood sugar, but it’s also lipolytic, so it’s both „bad“ and beneficial.