"If it came from a plant, eat it. If it was made in a plant, don't."
It's all about nutrient density. Processed foods will fill you with calories quickly, but still leave your body starved for nutrition. Plant foods are low in calories and are loaded with vitamins, enzymes and minerals that your body needs for optimal functioning.
All the tips given for the 28 Days of Real Food Challenge were compiled from "Food Rules", by Michael Pollan.