I once had a co-worker ask me what my secret was to dropping 30 pounds (down to 162 or so, my normal weight) in a matter of about 6 months. I told her "well, I run 3 times a week and I substituted all of the crappy food for healthy stuff". She wasn't really stoked about my answer.
I used the glycemic index. A great way to eat that doesn't involve eating only a few types of foods or eating tiny portions. Low GI foods are good. High GI is bad. Pastas, long grain rice, whole grain bread, fruits are all good for you. So why use a diet system where you have to eat a carrot and a carton of apple sauce for lunch, or a crappy frozen entree for dinner?
Not a quick fix, but if you're exercising to get healthy (not just to lose weight) and want to try changing up the diet, give it a try!