When people talk about "treating" autism with diet or anything else, the terminology causes me to cringe. I was diagnosed with Aspergers when I was in Elementary school, as were my two brothers (my poor parents with their fleet of abnormal antisocial children!). My youngest brother ended up being diagnosed with what would be considered closer to autism, while as we grew up it was largely agreed that myself and my older brother had been misdiagnosed. My older brother and myself had developed our reading/writing/number skills very early, my older brother in particular being tested for exceptional math skills when he was only in grade 3. While my older brother and I were slow to develop social skills (hence the diagnoses), we eventually caught on to the whole process and the diagnoses was essentially "removed" from our student records etc. My younger brother on the other hand still has social anxiety, antisocial tendencies, experiences "sensory overload" as we say in loud/busy situations, has a preoccupation with smelling objects he comes in contact with, extreme discomfort being touched (mostly w/strangers), a brutally high IQ, avoids eye contact, has a "near photographic" memory, has a knack for learning foreign languages, and is still considered to have Aspergers or maybe something slightly different along the autism spectrum disorder. Through this combination of extensive family experience, my mother (then a psych nurse, and the daughter of a schizophrenic with an autistic brother) did extensive research and when I got old enough I joined in the familial pursuit of knowledge.
One of the main issues I have when I look at any product or plan is the idea of "treating", "curing", or "fixing" the autism spectrum disorder (ASD from now on). The fact is, autism is not a disease. It cannot be somehow purged from your brain and it is not something negative that should be fixed. It is a condition- a state of being that is slightly different and has been around since the dawn of time. To get rid of the ASD would be to change that persons entire being at the most fundamental level. Yes, ASD is not a walk in the park, and for every genius with ASD that is revered on the internet there are always struggles that you just don't see with day to day tasks that is an undeniable strain on some parents and caregivers. When you do anything for a person with ASD, all you are doing is help them manage some of the aspects of their syndrome, and that is how it should be talked about. It's all about managing all the physical and behavioral aspects that are associated with the syndrome to make the lives of those with ASD, and the lives of the caretakers, easier and more pleasant. Nothing is going to change who you are as a person underneath it all- that may sound over dramatic, but it's an important distinction, and as someone who has hunted for information I am tired of people offering "cures" when that is not at all what I want for my brother. I just want him to be happy and healthy!
I think it remains that improving your health will give you more manageable moods, less physical discomfort, and more energy, whether you have ASD or not. It may be more noticeable in those with ASD, especially when verbal communication is not entirely present- sometimes the only way my brother knows how to communicate how he's feeling is to cry or have a fit. It may be shocking to some people when my brother starts crying in public, because he looks like any other 19 year old teenager, but for him it's his way of letting us know how upset he is. When he is feeling better (in good health, has lots of energy) he is better able to manage his emotions, which allows him to communicate to us in a more effective way. There is also has been an observed link between autism and more issues in the digestive tract, which is one of the physical manifestations (and possibly associated coincidentally with genetics) of ASD. This means a greater sensitivity to diet- my brother started getting hemorrhoids when he was in his early teens all of a sudden, and frequently experiences constipation (which my other brother and I never had a problem with). All these things point to the fact that a diet that is high quality, nutritious, and possibly supplemented (vit D) will make a person with ASD feel and then act more optimally. It, however, will not "treat" away the disease. If you took away the ASD my brother would no longer be my brother- and that should never be the goal.
I applaud parents for providing as healthy an environment as possible for their children who have (not suffer from, HAVE) ASD- it is not easy to raise an "abnormal" person that others want to "fix". I have seen many, many, MANY, many claims for a "cure" that I believe are at best disrespectful and at worst a dangerous suggestion to vulnerable parents willing to do (and pay) anything.