I see from your last sentence your fast is going well!
I've never really known if I've ever been fat-adapted to be honest. I did spend about a month on about 20-50g carbs, always aiming for the lower end, and presuming I was probably in ketosis, but I suppose I can't be sure.
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I think from what people say fasting either gets better the more often you do it, or the longer you do one, or the more 'fat adapted' you are. I'm not sure how fat adapted I've ever been - I did aim for ketosis for about a month but was very aware that I was often getting up to the 50g carb mark so I'm not sure to be honest. Either way, whenever I've tried fasting I get mental fog. That's not to say fasting hasn't been extremely useful to me on three occasions now.
If you're getting brain fog, it possubly means that you're usuffering from a sort of low carb/keto/Atkins "flu" - you've used up your available carby glucose fuel, but haven't yet got to the point where your body has (re)learned to use fat as well as those carbs as fuel - i.e. become fat adapted, so shortage of fuel to drive your body and especially your brain could mean you're feeling well and truly clobbered.
On a higher carb diet carbs are an easy and quick source of fuel that gets topped up with frequent. high carb meals and snacks, so our bodies forget how to use ttheir vast fat stores as well.
You just need to go low enough carb for long enough to persuade your body to switch (back) to using both carbs and - preferentially - fats for fuel. It's a permanent change to your body chemistry and unlike simply being in ketosis, you can switch easily between (some reasonable amount of) carbs and fats as required - easy carbs used up first, dietary fats then stored fats last, and your body is actually intended to work this way. Carbs are quick and easy fuel but need topping up all the time,while fat/ketones offer a continuous steady supply so you should feel the difference, and you shouldn't feel knackered when gallivanting up and down Snowden at top speed ... and as
@ickihun suggested, mental clarity is an importanty benefit too. Last but not least you lose those carby craving and have no further need of constant re-fuelling to be able to work and think well.
(Thinking about it, fasting for longish periods is probably a more drastic but faster method of getting to where some serious low carbing eventually gets you? And so, yes, it should get better because you have, with practice, learned how to access your stored fat fuel reserves to keep you going in place of food during your fast.)
Robbity
