Well, I'm new here, but I do have experience with this. I could write six pages on this, or I could just give you some links and invite you to ask questions if you need to.
We do GFCF diet -- that stands for gluten-free, casein-free. It has worked wonders for our child with autism, and we have since found out that four of us need the diet in this family, thanks to some testing that identified it. We all feel much better, even though some of didn't even really have symptoms of gluten intolerance.
Also we try to avoid corn syrup -- it's a dirty, cheap additive that turns into what it is by devious means. We also don't do food dyes. We are not terribly strict about the corn syrup and food dyes-- if we go to a party and the only thing my son can eat is a fruit roll up, because they are serving pizza and cake, then we eat the fruit roll up. But overall, it helps.
Start with
www.gfcfdiet.com and
www.danasview.net
A lot of these talk about autism, but research shows that the diet works for other issues that experts now believe are on the autism spectrum -- such as ADD/ADHD, tourettes, and children with behavior and anger problems.
Ask me questions. I have lots of articles and links.