I have lost 25kg (55 pounds) over a course of a year. Half of that was intermittent fasting (one day eating for about 10 hours, then no calories for the rest, about 38 hours) but accounts for 3/4 of results.

When not eating I would not eat or drink anything that has any calories in it. I typically drink water, black coffee or green tea.

I have also tried longer fasts from time to time (2-7 days typically, 2 weeks once) and then I would supplement with vitamins, l-tryptophan and lean broth/bone broth in moderate quantities (a cup a day), just for safety and general well-being (l-tryptophan is precursor to serotonin and mildly anti-depressant).

Intermittent fasting is hard at the beginning but after about 2 weeks I get used to new regime. It seems it is the same every time I start it anew. It might be getting easier but I think that's because I already know what to expect.

Also, when intermittent fasting it is much easier to start longer fast. I find, when fasting for more than 2 days first two days to be the hardest.