1. Artificial - typically will be used for coloring and sweeteners. These nasty products have been shown to cause ailments from weight gain to neurotoxicity (brain poison).
2. Modified - Nature is pretty darn amazing. It's supported man for millennium. But here we tried to make it better.....we failed. These products (usually corn and soy) have had their genes twisted and changed. The problem? Our bodies don't recognize it as normal leading a variety of conditions. Look up the EWG.org or the Cornucopia Institute for more info.
3. Hydrogenated - Remember all that stuff going on about Trans fats? Well, they can still be hidden by weird labeling laws. How do you find them? Look for the word hydrogenated. This is giving you a clue that something has been altered in your food.
Ultimately, it goes back to the basics. Eat what supports you. And what supports you is what is supported by nature. But you have to read labels! Happy Health Food Hunting!