We have eliminated many foods b/c the behavior they caused was UNBELIEVABLE!
Dairy was an obvious one from infancy--hives and excema, too. But the hyperactive, crazy, VIOLENT behavior was unreal. Now, we've found most fruits are out. It's the stalycilites (spelling?)--there is a list on the Feingold site that lists foods containing them. My kid can be getting along fine--happy and cooperative, but give him a handful of grapes? Holy Hell! He is angry, contrary, quick to tantrum, hyper, and violent. It is shocking how radically his behavior changes! Grapes for goodness sakes! Who would ever suspect that??
Almost all his food allergies (citrus, citric acid, eggs, peanuts, dairy, stalycilites) manifest themselves in behavior. Some of them have physical manifestations, too. Those are neglible, though--a small patch of dry skin on his leg, a red spot on his cheek or chin, slight rash on his chest, etc.
I always wonder how many families are dealing with over the top behavioral stuff that is a direct result of food--NOT a "disobediant" or "naughty" kid.