I didn’t have keto flu. I heard it’s about electrolytes (I was lucky as I didn’t supplement anything but my body handled it well. I felt some tiny dizziness but so little it could have been anything and it was 2 days and VERY subtle indeed, it caused no problem). Then I’ve read even carb withdrawal can cause it, well I lowered my carbs gradually enough not to have that problem either.
But I never heard someone having problems after 3 weeks, it usually comes in a few days.
I have no idea what real flu feels like as I never had that either. But if I have problems right when I get into ketosis (after a few days on keto), I suspect lack of sodium now. But lack of other electolytes can be the problem too as far as I know. In my case, it’s probably sodium just like cramps always signal lack of magnesium in my individual case. If there is a problem, make sure you have enough electrolytes and if you still have problem afterwards, it’s probably something else.
That’s about all I know about this.
And that you can expect a way longer time until your brain get used to ketones. Workouts often are less effective too for some while. My brain stayed the same (no brain fog or later a higher level of mental clarity, just what my normal) and I didn’t do workouts in my first keto months.
Waking up tired and unwell happens in my life too, I think it’s quite normal but it has nothing to do with keto or any kind of “flu”.
Running in the cold rain can cause a cold even in the case of a very healthy person who never gets the flu… I would think that is the reason but one can never know.
