Edit:
Also, the benefit to cognition that you mention is sort of like a secret because I never seen anyone mention it. When I first started on a "keto" type of diet I woke up one day with a feeling which was like being wired on coffee but without the jittery side effects. Except, it didn't go away. I would have thought I broke something if it wasn't such a positive. It's amazing to think that's how we should be feeling and that nearly everyone is working below this level.
Personally, I got distracted, had a bunch of changes at home and failed out of it. I'll be climbing back on after the holidays.
I still like to drink coffee in this state, though I limited my intake to one cup every couple of days. Nicotine seemed to be neither a negative or a positive. It didn't cause more or less problems for me. I could also drink beer with no problems.