If you're looking for a way to drastically improve your brain function without resorting to nootropics, I have yet to find anything better than Ketosis + Intermittent Fasting.
A word of advice though, you really need to keep your diet loaded with healthy fats, and don't over-do the protein! I kept kicking myself out of ketosis by consuming my usual daily amount of protein (about 200 grams). I keep it to about 100 grams now, which is still enough to keep a positive nitrogen balance (and therefore build muscle slowly if that's a concern). OMAD is:
- 8 egg french omelette w/ cheese, avocado, sour cream, nutritional yeast - Veg (carrot, pepper, crimini mushrooms) sauteed in lots of olive oil and a bit of bone broth/stock; finished with lemon juice.
- Between the omelette and veg dish, I used about 100ml of olive oil (about 800 calories worth). This is how I drastically increase my Fat to Protein ratio (other than limiting protein to about 0.6 grams per pound of bodyweight). I have actually gained muscle and lost fat on this diet; although not a great deal since I'm not on anabolics.