Whats your goal, age and starting bodyfat percentage?
On a long fast like that there’s no silver bullet to feeling good beyond electrolytes and walks. Once you start feeling bad it’s time to break the fast, simple as.
Beforehand you should avoid carbs or even switch to eating keto a few days. This will be hard if youre not used to keto(you might get keto flu) so I’d suggest just very low carb. This makes it a lot easier to switch to fat burning
While you’re fasting, there are really only three things I’ve found that can help. electrolytes, of course. caffeine, can help give you a little boost and lessen appetite a little. and MCT oil, which is a fat that gets converted to ketones so it’s taking in calories BUT you stay in ketosis and it gets burned off. So obviously it wouldn’t be a ‘pure’ fast, but honesty what does 200 calories across a three day fast matter.