Everybody needs a little fat in their diet. Organs like the brain require it. And while all types of fat can cause weight gain, some fats are better than others. Avocados, for example, contain loads of healthy, monounsaturated fat, which boosts the body's production of acetylcholine, a chemical that helps the brain learn and remember. It also allows the brain to absorb the fruit's numerous vitamins, including B, C, E and K.