Food used to be simple. You ate what you grew on the land or you bought from nearby farmers. Processed food was nothing more than canned, frozen, or cured. Today, food is much more complicated—and we're both better and worse off for it. We can eat a greater variety of healthy foods than our ancestors did (think fresh berries in winter), but we also can eat a lot more highly processed, chemical-laden ones. And that fare seems to be winning the day, if our epidemics of obesity and diabetes are any indication. (Make Prevention's Eat Clean, Stay Lean your go-to clean-eating guide, with 300 real foods and slimming recipes.