Become a pro at reading labels!
When you buy foods at the store, you’ll see that most of them have a label that tells what’s inside. What’s inside is listed in order of "most to least." So, if a wheat bread label lists "bleached white flour" (flour that has been processed so it looks whiter–or bleached) as the first ingredient, and then the second ingredient says "stoneground wheat flour," you know that it’s not purely wheat bread—and you’ll know it contains more processed flour than naturally wholesome wheat flour.

The more you read labels, the wiser you’ll be. If you start reading and you see lots of long words that you can’t pronounce, chances are you’re looking at a lot of processing going on–and you have to ask yourself, "Do I want to eat a food that contains so many preservatives, food coloring, etc.?" That’s when you should compare this item with another food, and see what sounds healthier to you.

To learn more about reading labels, check out these sites:
Figuring Out Food labels
Kid's World Nutrition Information

What if the food doesn’t have a label on it?
If you’re looking at fresh fruits and vegetables, and meats and eggs and so on, you’ll see they are marked somehow, somewhere, with information that tells you where they come from and how they’re grown. If they’re grown organically without synthetic chemicals and meeting certain high standards for being chemical-free, they’ll be marked "certified organic." (If they are not marked "organic" you can assume they were grown using pesticides and other chemicals.)