Is drinking straight coffee or tea bad on any fast?

Don't know too much about fasting, but started my first fast yesterday morning, been about 30 hours with only some collard greens juice, fasting tea (Yogi), and various black and green tea (no sweeteners) to get through the day.

Reading up on this site and others to learn more - I see that neither water nor juice fast says you can drink coffee or tea.

Just wondering, what is the harm of drinking coffee or tea if there is zero calories, and it won't break your fast? (Note: I know drinking zero calorie soda would be counterproductive as those are toxic, but I figured straight coffee and tea would be OK).

Many thanks for any input! Tweet