#2 Don't eat anything your great-grandmother wouldn't recognize as food.
Imagine your great-grandmother (or grand-mother, depending on your age) at your side as you roll down the aisle of the supermarket. You're standing together in front of the dairy case. She picks up a package of GO-Gurt Portable Yogurt tubes-and hasn't a clue what this plastic cylinder of colored and flavored gel could possibly be. Is it food, or is it toothpaste? There are now thousands of foodish products in the supermarket that our ancestors simply wouldn't recognize as food. The reasons to avoid eating such complicated food products are many, and go beyond the various chemical additives and corn and soy derivatives they contain, or the plastics in which they are typically packaged, some of which are probably toxic. Today foods are processed in ways specifically designed to get us to buy and eat more by pushing our evolutionary buttons-our inborn preferences for sweetness and fat and salt. These tastes are difficult to find in nature but cheap and easy for food scientists to deploy, with the result that food processing induces us to consume much more of these rarities than is good for us. The great-grandmother rule will help keep most of these items out of your cart.
Note: If your great-grandmother was a terrible cook or eater, you can substitute someone else's grandmother.
-Michael Pollan, Food Rules