If you look on page 3 I posted an article I found in a magazine on an ADHD diet. I thought it was interesting. You can try it and see if it works. It should still be on page 3 or 4. The post title says ADHD diet in it. Best wishes!
Definitely look into the Feingold diet as it is a good starting point. (www.feingold.org) Two of my kids cannot have food coloring and one can only have reduced salicylates (e.g. apples, berries, tomato products). The diet has you start with a 4 week elimination diet which clears the body - we noticed a huge difference in 2 days. Then you can slowly introduce food items and track whether they cause any issues.