Hey, listen, do whatever you want, man! EAS recommends the famous CHEAT day where you pig out on anything you want, and others share a similar strategy called a Cheat Meal. The problem is when you take it from a cheat meal or cheat day and start subbing in crappy foods regularly...even in moderation, it's going to bring you down somewhat.
Vtec96 is right about Olestra giving you the shits and it also affects absorption of nutrients so the rest of your meal might go through your digestive system but you got a fraction of the VALUE from it that you're eating it for in the first place. Not just to satisfy hunger, but to buff you up.
In general, processed foods are to be avoided, but if you want, include them all on one cheat day. I think part of the plan of a cheat day is not purely psychological, like letting the dog tear a pillow apart, but physiological. Cheat days or meals can often cause a shitload of physical pain, not exactly, but similar to loading up on carbs right after low-carbing....it just floods you with crap to excess. After a while, you'll automatically moderate yourself on the cheat days because not cheating just feels better. But you have to cheat like a wild pig once a week to get the full lesson.
Good luck, cheating, pig. j/k
B