Getting enough liquid in your system is super important since your brain is about 80percent water. It won't function as well if you're dehydrated. So make sure to keep drinking water all day, at least 8 6-ounce glasses. It's also a good idea to drink fruit or vegetable juice, Polyphenols, which are the antioxidants in fruits and vegetables, help protect brain cells from damage and keep your brain at a high-functioning level.