i've just had a thought: do you mean packaged food (any food that happens to be in a package, including rice) or processed food (e.g. meal-in-a-box, shelf life of 400 years)? By which I mean, is this some kind of Transcendentalist diet, where you only consume raw vegetables whose root gatherings are under six inches long, or is it more of a "Gee, I should really cut back on the chemicals" thing?

If you're trying to wean yourself off of additives (which i've had to do, so i know how tough it is), the most important thing to do is to read labels very carefully. You'd be amazed at what has Red 40 in it. Or Yellow 5 and 6. Breakfast cereals--even the "healthy" ones are awful about this.
Also, the dread high fructose corn syrup...