I would love to try this - but certainly dont have 5 consecutive days where I can be a mental vegetable.
The brain needs constant fuel. Anyone experience this as well?
These days, I can feel my body switch modes when I enter a low-glucose state. It's a certain type of relaxation that feels like my brain just stops running certain programs. For example, it can't afford to hold on to dramatic, powerful emotions in that low-fuel state, and so it stops running its "replay enraging memories" program, so to speak.
You're correct that the brain needs constant fuel, but we have an unbelievable source of fuel in our bodies called fat. Increasing the metabolism's flexibility, such that it can gracefully tap into that massive fuel source, has had a noticeable impact on my mental and physical health.
IME, it's more like a hump you have to get over, for what that's worth.
That is true, however that fuel does not need to be glucose. As far as I understand it, people eating 3 meals a day and snacks (all containing carbohydrates), their body is not used to relying solely on fat/ketones for energy, and it takes time to adjust.
Also, it's very important when fasting to ensure you're replacing water and electrolytes since once you've burned through your stored glycogen you will have lost quite a bit of water. If you're feeling light headed or out of it, that is one of the causes, whether you're starting a ketogenic diet or fasting.
When I'm fasting I use an electrolyte mix which has sodium, magnesium, phosphorus, potassium and calcium. One of the main reasons for refeeding syndrome is that electrolytes are depleted, and when someone eats again, their cells take up what little electrolytes are left in the blood, which leads to dangerously low levels.
In a sufficiently fasted state, all of that glucose will be endogenously produced rather than coming directly from food, but it does need to be there.
I have found that once I become fat adapted, I no longer suffer from mental clarity problems. It takes a couple of days without carbs to get there for me.
Your noradrenaline levels spike when fasting, and it can make it hard to sleep - too juiced haha.
If you're finding yourself tired, it could be a lack of electrolytes. Try a teaspoon of salt in a pint of water. I tend to drink coffee when water fasting, which has an outsize effect.
My sleep was pretty terrible up until the last night, when I got a solid 8 hours without waking up once. I usually wake up 8-10 times a night, so this was a huge breakthrough. I also regained my energy on that last half day and felt incredible.
What type of fasting did you do, and what liquids did you drink?
I do prefer resting physically when fasting, but the mental clarity is unparallelled after 24 hours.
Also watch your electrolytes. Salt, potassium and magnesium can greatly affect energy levels.