#13 Eat only foods that will eventually rot.
What does it mean for food to "go bad?" It usually means that the fungi and bacteria and insects and rodents with whom we compete for nutrients and calories have gotten to it before we did. Food processing began as a way to extend the shelf life of food by protecting it from these competitors. This is often accomplished by making food less appealing to them, by removing nutrients from it that attracted competitors, or by removing other nutrients likely to turn rancid, like omega-3 fatty acids. The more processed a food is, the longer the shelf life, and the less nutritious it typically is. Real food is alive-and therefore it should eventually die. (There are a few exceptions to this rule: For example, honey has a shelf life measured in centuries.) Note: Most of the immortal foodlike substances in the supermarket are found in the middle aisles. -Michael Pollan, Food Rules