IMO..... modern "fasting" is typically the temporary abandoning of something that is believed to be hindering our relationship with God.
IMO.... the best thing to fast from is sin, but....
IMO.... in the Bible (and it seems to me in the earliest church) often FOOD was what was abandoned (although obviously not typically for long - I know of few cases where people DIED of starvation BECAUSE they were fasting). And if food is something that is harming ones relationship with God, it might be good to fast from that.
I have proactively fasted twice in my life. Once, as a boy and still Catholic, I fasted from TV. I was watching way too much of it and gave it up for Lent. I didn't intentionally watch it at all for those 40+ days. And I TRIED to fill the void with Bible reading, prayer, Rosary, etc. All in all, it was a good thing, I think. Later, I "fasted" from the social internet.... websites (like this one!), Facebook, etc. I not only was spending too much time, but I was WAY over involved, too emotionally dominated by it. I have it up for Lent. Tried to fill in the time with REAL social connections and with Bible reading, devotions, prayer, study and church service. It was good.... and I never again got SO intertwined (in fact, I never really returned to facebook and stuff again).
IMO, fasting such as that CAN be helpful. But of course, it can also actually hinter our relationship with God if we become fixated on our "loss" (what we gave up) rather than God..... if we begin to think ourselves more worthy because of what WE did..... in those cases, it is a great harm.
Pax
- Josiah