Hmmm... food poisoning, juice only til I could keep food down...
Actually I guess my answer would be "long enough". Sometimes with fresh veggie juice once a day, sometimes with only water. Physical affects: I got
really hungry, and lost several pounds short term. Once I dreamed about eating all night, and another time I woke up having dreamed that I went to come off the fast and there was NOTHING in the house to eat. I went to the grocery store that morning and bought more groceries than they'd probably seen me check out with in a month.
As far as miracles and answers, once a man stopped stalking me for a few months afterward, but that wasn't why I fasted and I'm not sure there was any relation between the two events other than timing.
But I love these verses:
Isa 58:4 Behold, ye fast for strife and debate, and to smite with the fist of wickedness: ye shall not fast as [ye do this] day, to make your voice to be heard on high.
Isa 58:5 Is it such a fast that I have chosen? a day for a man to afflict his soul? [is it] to bow down his head as a bulrush, and to spread sackcloth and ashes [under him]? wilt thou call this a fast, and an acceptable day to the LORD?
Isa 58:6 [Is] not this the fast that I have chosen? to loose the bands of wickedness, to undo the heavy burdens, and to let the oppressed go free, and that ye break every yoke?
Isa 58:7 [Is it] not to deal thy bread to the hungry, and that thou bring the poor that are cast out to thy house? when thou seest the naked, that thou cover him; and that thou hide not thyself from thine own flesh?
Isa 58:8 Then shall thy light break forth as the morning, and thine health shall spring forth speedily: and thy righteousness shall go before thee; the glory of the LORD shall be thy rereward.
Isa 58:9 Then shalt thou call, and the LORD shall answer; thou shalt cry, and he shall say, Here I [am]. If thou take away from the midst of thee the yoke, the putting forth of the finger, and speaking vanity...
The rest of the passage is really good too...
Results: I was more considerate of others and their needs, and thought a lot about how I might have been physically hungry, but others are spiritually starving:
Amo 8:11 Behold, the days come, saith the Lord GOD, that I will send a famine in the land, not a famine of bread, nor a thirst for water, but of hearing the words of the LORD...
Coming to that realization was the only miracle I needed.