What is the best food for the brain?
It depends on your purpose of this question, because, it can be understood in two different ways, some will think you are talking of nutrition for the brain and its function and some may understand you referring to knowledge.
In terms of nutrition for the brain, it's quite funny, actually, I found each family and community, got their type of food which they bet on as the best for gains better productivity of brain, and you can find each grandmother on different societies, got their own recipe for some brain's functions, like my grandmother says the food to make your memory as good as hard disk things are 7 pieces of a raisin in the morning with a dry throat, or for better understanding, you have to put thyme with your meals, or eat a lot of chocolate - maybe my mother who will say that because it's a modern method 😬- but in other cultures, you will find another recipe as a traditional food for gain brains functions.
On the other hand, if you asking about how to feed your knowledge and get a better understanding of things in your life and being wiser than your grandfather, then it's READING, but little who take it seriously and consume it, and there are also great ways to have massive knowledge such as learning another language, and getting to know how other people live in the other side of the world and combine their perspectives to your own to make your unique way of seeing the world.
With all said and done, in my opinion, the main thing that will feed your brain and gain your knowledge and better productivity is learning and the best way to learn is reading because when people write books they try to summarise their years of learning in several pages which will basically give you the gist of their experience, after that when you become a good reader you may take some recipes to enhance your brain as a brain's luxuries.