Some of the very basics I know from researching veganism:

Moderate meat-eaters seem to have longer lifespans than heavy meat-eaters and vegans. I can't remember if vegetarians are equivalent or a little shorter. This is epidemiological data so take it with a grain of salt--you can eat french fries all day and be considered a vegan, likewise many vegetarians probably substitute meat with unhealthy amounts of cheese. But eating meat-heavy meals for every meal appears to be bad for longevity.

Fish is effective at preventing alzheimer's. This does not seem to be reproducible by taking (overrated) omega-3 fatty acid capsules.

So, eating more vegetarian dishes and fish once every few days or so is probably a good idea. I have no clue what to help with short-term cognitive performance.

Also, moderate wine consumption is extremely good for you. 3 glasses a week can increase your lifespan significantly.