I just went to see an autism pediatrician today, he is in Sydney and his name is Antony Underwood. He uses biomedical approach, and also homúopathy and Rudolph Steinerís anthroposophy. He was so lovely, he listened to me and didn't make me feel like an idiot, like the other doctors do.
My daughter does not have autism but she has AD/HD with some autistic characteristics, and severe digestive problems. The only things she could eat where rice, lamb and a little bit of broccoli or potato. As I breastfed her til she was 1, I had to eat that also! She screamed after every feed so I had to cut my food and her food back to just those four things (though too much broccoli gives her insomnia).
She is salicylate sensitive, and preservative/additive sensitive. In Sydney there is an amazing network called FailSafe Eating, you can find out more on Sue Dengate's site Fed Up with Food Additives.
But you can go crazy trying to find out which diet is right. You could also do casein/wheat free (which we don't do), or the Specific Carbohydrate Diet (which I am thinking of trying). You need a dietition to help, at least initially, then you can experiment!
There is light at the end of the tunnel. If you need more info, feel free to PM me.
Much love, Simone