We strongly suspect that DD (4.5) has symptoms of this. Having spoken to the HV we are on a 3 week dairy free trial with her to see how that goes. School haven't flagged her up as anything more serious than rushing through tasks and being an incurable chatterbox, but after a few incidents of dairy-rich foods being followed by pale face, dark circles under eyes, interminable fidgetyness, speaking utter gibberish, interrupting constantly and speaking at volume we have decided to see if the uncontrollable nature of her personality are lessened in any way without dairy. She was strongly CMPI as a baby with raging reflux, blood in stools and diarrhoea. She was also intolerant of wheat/gluten until she was 2 so this is also at the back of our minds. I hadn't suspected diet was causing her impulsiveness (she is a very confident and outgoing girl) until we trialled DD2 with dairy after her reflux issues and she was so hyper the childminder commented on it, and we hadn't told her about the trial in advance so it wasn't just us.
I don't know much about allergies and behaviour at all so was wondering if anyone has any dc with similar issues?