I am a firm believer in diet being a part of treatment for ADHD and other issues too. I have seen diet work wonders on my household.

But what you need to do is a proper scientific elimination diet, in australia I would recommend the royal prince alfred hospital elimination diet handbook, figure out what YOUR child can and can't tolerate and only eliminate those foods, and only with the support of a skilled dietician.

The most likely culprits are gluten, dairy and salicylates. But it could be amines, fructose, or various other things.

My eldest is: dairy, gluten free, extremely low salicylate, extremely low fructose and moderate amines. This child is a dramatically different child on her diet.

My middle child: just gluten and dairy free, she can gorge on the rest to no effect. This child lost the least foods and also has the least impact from a mistake, she's my most normal child.

Youngest child: is pretty much every thing free, she has a list of what she CAN eat that is shorter than what she can't... This child possibly has a genetic disorder and we are awaiting gene test results.

My husband is most like #2, I am most like #1. We are ALL much healthier and happier than we were 2 years ago.

For a child with a real problem diet alone is rarely enough.