You avoid food by not eating. And, if that is what you want to do you are a very mentally unstable person. If you mean what kind of foods to eat to be healthy, then look at any healthy diet section...
You must avoid having food between 41° and 135°
it will explode in their face!! things like achohol and ither fizzy things will sooner or later be on their face!! =)
You want to avoid eating metal!
Junk food should be avoided.