Some do indeed stick with what is commonly called “clean fasting”, which limits virtually anything other than some teas, water, and black coffee. The logic being that artificial sweeteners increase blood sugar, insulin response etc (though do note that there is no definitive scientific evidence that this is the case).
Clean fasting proved far too difficult for me personally, and I abandoned this fairly early on in my tenure in this gig. I only eliminate calories, so I still drink diet soda, calorie free energy drinks, etc. Though according to some of the purist mindset folks mentioned in my above paragraph, almost none of my 4 years of doing this actually counts as fasting. Doubt I will lose sleep over this assessment.
What works best for you is something you will have to discover on your own as we are all a bit different.
Coffee w/ a bit of cacao powder (no sweetener). I limit to 10g/day, about 25 cal / 3g net carb, 1g fat. Theobromines keep you happy and suppress appetite.
Also about 25g/day fermented sauerkraut (NOT typical sugar+vinegar pickled). \~10cal, 2g net carb. Be sure to drink the juice. Keeps my flora lit, zero digesting issues (at least through \~90hrs).
I get the same outcomes in terms of ketosis & weight control as all-water, but side effects endured by many are non-existent.
Yes; I, too, am impure in my habits.
I don’t hear about it being talked a lot about here but a guy named Valter Longo created a fasting mimicking diet. I don’t know a lot about it but it’s something like sub 500 cals a day with restrictions.
But the majority of the time people here aren’t eating anything during these long fasts. Like you said water, coffee and tea for the most part.
I’ve seen a couple posts about liquid fasts like taking in bone broth too
When I do long fasts (I’ve done more than 3 weeks) I drink only water, and electrolytes. I need my electrolytes if I’m doing about 4 days or more. I do the pills, because drinking salt water makes me queasy lol
I have water and protein water (less than 300 calories). After my first water only of 20 days, I had a lot of hair loss so I supplement with the protein water to reduce that loss, which it has. It put the prolonged fast fear in me so I do maybe 7 days at most lately. I am working back up to 10 days and beyond.