Is there any evidence that black coffee or other sources of caffeine can affect blood sugar in a fasted state? I have heard that caffeine might cause blood sugar swings, but I'd like to have a second opinion. I love my coffee, although I drink it for the taste and not for energy. But I'm trying to get back to my old IF habits, which felt great. I just don't like the thought of playing with my blood sugar while fasting. Any thoughts/links/anything?