cant disagree on the carnivore/keto argument, the 14 months i did carnivore i was very strict about it. after the initial "keto flu" symptoms my brain was firing on all cylinders, mental clarity was without a doubt at least double what it was previously, i had sustained energy that seemingly never ran out, sleep was amazing.
downsides however, that sustained energy was sustained for a normal load, lighter workouts, some cardio. trying to do heavy workouts is where the cracks really showed without any carbs. cholesterol obviously another issue, those numbers all went up higher than i'm comfortable keeping them at regardless of how many youtube carnivore doctors say its perfectly fine.
as soon as i was back on a balanced diet with carbs, brain fog came right back, no more steady energy levels, sleep terrible, but gym gains undoubtedly improved which was no surprise. for me carnivore served its purpose, dropped over 120lbs in less than a year and its stayed off but i wouldnt try staying on carnivore as a permanent diet plan. wish i could have that mental clarity and sleep back though