The "rule" is that you can put whatever you want on that plate. However, a side effect that pretty much everyone has is that since they are forced into smaller portions of food, they are more likely to consider what goes onto that plate. Most people are vaguely aware of what's good for you and what's bad for you, in a general sense. Plus, this diet is more for people who eat too much. Once you're eating a reasonable amount of food, it's easier to switch to better food, since you know you have to get the good stuff (fruits and veggies, for the most part) in there somewhere. :)