I think one of the central premises of primal is that a carb ISN'T a carb. There are carbs that are awesome for you, carbs that are kinda neutral, and carbs that are really not good for you. Nothing to do with calories, everything to do with insulin response and chemicals in the not-good-for-you carbs. Wheat is seen as a bad carb (along with all grains) because of chemicals within it.
I think arrowroot is preferred because it isn't a grain.
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food