I would suggest going to the disABILITIES Forum and look at Post #3 of the disABILITIES FAQs. There is a large section in that post dealing with special dietary needs, as well as many related links. You can get directly to the disABILITIES FAQs by following the link in my signature.
This is a very common topic of discussion in the disABILITIES Forum.