Behaviour problems often coexist with allergies.

Allergies can result in children being over or under responsive to sensory stimulation, particularly sound and touch.
The solution to some behaviour problems is identifying and eliminating potential food allergens, and environmental irritants e.g. mould. Once these have been identified and removed, symptoms associated with behavioural problems due to sensory processing disorders and allergies can sometimes resolve.
Common foods associated with allergic reactions in ADHD children include:

Corn products
Dairy products
Eggs
Nuts
Peanuts
Soya
Wheat
Fish