...Is avoiding what you DON'T want, while getting what you DO want.
My best guess is to avoid commercially-processed foods, and those 'treated' in some way, either in growing, or in marketing. We don't always know, unless we develop a sixth sense for this purpose.
I feel it is best to grow one's own, on virgin land, with great compost; or make friends with someone who does.
Read Eliot Coleman...Four Season Farm. http://www.fourseasonfarm.com/ He's a genius. His carrots are the coin of trade among local schoolchildren.