There are studies showing positive health outcomes for ASD on a gluten free diet, as well as for epilepsy and schizophrenia. Here [1] is a comment with some links, the featured article might also be interesting.

I have a lot of food allergies and a restaurant in Maryland that specializes in restricted diets pointed some of the research out to me. You can find scores of families with ASD children who have found dietary interventions to be beneficial.

The studies I have seen talk about something called exorphins, it sounded like people with ASD's bodies treat gluten like an opiate.

1. https://news.ycombinator.com/item?id=39194978