Ok, so some research shows brain function actually improves when running on ketones; that they are the brain’s preferred source of fuel.
Problem is, if you’re just using the <200g CHO as an arbitrary number, you’re not using ketones. There is a huge difference between <200g CHO and <50g CHO (per day).
The <50g CHO ensures ketosis is reached within 3-5 days, as the brain itself needs about 50g glucose per day, or it will seek an alternative fuel source.
As JMo pointed out, if you are in ketosis, after two weeks (sometimes sooner) you will feel great.
So basically, either bite the bullet and seek ketosis (<50g CHO per day) or don’t, and keep the carbs in.
Fat can be lost at an optimal rate, either way.[/quote]
Also, the fogginess you’re experiencing can be from just overall low calories. If you remove a large part of a macro from your diet, you should place the calories with another macro.