I did the same thing when I was very inexperienced with fasting, I would drink a little coffee, or tea or broth or lemon water during the first few days and it did seem to help at first, but then I figured out it was probably part of the reason I could never make it past day 3. I think it definitely keeps you hungry. I also find that at some point I only want water and the thought of anything else sort of turns me off. I did take a few sips of someone's diet drink while I was about 2 weeks into a fast and the chemical taste of it was overwhelming to me. I think it's probably OK to drink different types of water although I think I read somewhere that sparkling water isn't good on a fast but I don't remember why.