Most Helpful Guy
I'd say once a week, max. I actually believe in avoiding those foods entirely, but I'm sure most people would consider me a bit excessive in my beliefs there. I mean, @iron_man hits the gym like crazy and he admits to having those Burger King $1.49 for 10 chicken nuggets for dinner at times. That's something that I'd NEVER do, yet I'm pretty sure that he could fold me seven times if it came down to it.
So yeah, while I would cut out those foods entirely (except for maybe a couple times a month if you absolutely must), I think it's pretty clear that you don't NEED to cut them out.
Most Helpful Girl
Just have a cheat day once a week, where you can eat what you want.