I've done intermittent fasting, ie. water only a couple of times last year.
First time for 24 hours and the second time a week later for 72 hours.
I lost a lot of weight and felt much better. 24 hours was a doddle but it was a real struggle to get through the long stretch on the 2nd go. Headaches, lethargy, nausea and I probably only got through it because I'm retired and don't have to slog it out at work like you do.
I haven't done a long fast since because after the first one I read a bunch of posts on Reddit and they reckon you're supposed to drink an electrolyte mixture slowly over the three days and I just never got around to attempt sourcing the stuff here in Thailand.
I'm no expert but I reckon that chewing gum is a no no because it likely contains sugar.