I used to fast for spiritual/religious reasons. I don't do it anymore because it triggers biliary colic attacks. I do remember that it put me in a different frame of my mind. Sharpened my awareness in strange ways. I had to approach a certain way in order for it to work, too. It's hard to explain.
Yes me too. The religion I grew up in, we would fast once a month for 24 hours, give the money you would have spent on food to the poor. Although I never experienced sharpened awareness. Just cranky or sad, weak, exhausted. Other people mentioned a heightened spiritual sensitivity, but I did not experience anything like that ever.