I know a lot of kids with seizure disorders use the ketogenic diet instead of meds to control their seizures. Maybe it would help with ADD, I'm not sure. It is usually overseen by a nutritionist and I don't think they have problems with losing weight. Maybe you could start by eliminating sugar from his diet and see if that helps.

I don't know how legit this website is, but I found this:

http://www.notint.com/disorders.htm
Attention Deficit Disorder (A.D.D.) - Every child or adult who has a learning deficit will have some sort of concentration and distractibility problem so this is not a proper criteria for diagnosis. A.D.D. is a special L.D. program with the same cranial deficits I find in Epilepsy. My feeling is that the spontaneous hyperactivity is really a manifestation of seizure activity. Both conditions are treated the same way with N.O.T. with excellent results. Another clue is that Epilepsy and A.D.D. respond very quickly to a Ketogenic Diet (no sugar).