My best advice is to calculate how much calories on average you burn during fasting and then think of a way to add them to your diet in form of calorie-dense and healthy food!
(!those numbers are just an example, calculate the actual numbers yourself!!!)
Let’s say you normally eat 2000 calories per day to maintain weight.You burn 2000 calories during 24h fast.You fast 4days so it’s 8000 calories lost.So for the next 8 days you eat 3000 calories: The base 2000 + 1000 until you make up for the calories lost in fast days.
How much water?
Drink. Drink until your urine is the correct colour. In fasting don’t rely on feeling thirsty. You’ll end up getting dehydrated (headaches and dizzyness are symptoms).
If you’re insisting on a number, I drink 3.5L minimum. I don’t know exactly how much.
Basically if you’ve gone like 8 hours without peeing, DRINK WATER IMMEDIATELY.
Don’t jump straight into a 7 day fast. Your body isn’t ready. Start with a few weeks of 16;8 intermittent fasting. Then when comfortable with this, switch to one meal a day (OMAD) and make sure you are at least hitting your TDEE in caloric intake. After a few weeks of OMAD, do rolling 36 hour fasts, but watch your calories - as a skinny guy the goal is not to eat less calories - it’s to eat less frequently. Once you’re rolling 36s comfortably - then consider extending from there.
Electrolytes buddy. Just make sure you’ve got 2L of water a day with some form of electrolytes chucked in, usually will give you a tiny spoon in the pouch. Well, mine did.
Think as long as you’ve got electrolytes then you’re fine.
This may sound outside the box in this sub, but at your height and weight, you may need to “bulk” in order to fast. You need some body fat to transition to after 72 hours. Otherwise, try bone broth, less than 50 cals, for sodium and a little protein.