Fasting has been around much, much longer than Islam. Indeed, mentions of abstention from food and drink can be found in the Hebrew Bible and the New Testament, both of which predate the Prophet Muhammad (who was born in A.D. 570). In one case found in the Bible, Queen Esther asks the Jews to fast for three days before she visits her husband, the king, to ask him not to kill them. And in the New Testament, Jesus fasts in the desert for 40 days, which is why to this day certain Christian denominations observe Lenten fasts.
The fasting itself is also different in Ramadan in that Muslim observers can technically eat each day, they just can't consume anything during daylight hours.