Anyone who’s paying attention knows it’s a very good idea to eat green, leafy vegetables and colorful citrus fruits. Over time, research has shown their association with reducing cancer and chronic disease. In fact, most of us know that we should be consuming multiple helpings of these foods each day. (Here is a handy calculator from the Centers for Disease Control and Prevention that helps you figure out how much you need.) But which vegetables are best? Fads come and go as quickly as that kale in your fridge. One day it’s broccoli, the next cabbage. And how do you...