it is a controversial subject, unfortunately.
I am another poster whose children have been helped, massively, by these so-called 'quack' remedies.
I don't do anything lightly, even if it is 'just' vitamins. everything I have ever done to try to help dd1 (in particular, but also dd2) has been documented well, for my own peace of mind. I have taken specific baselines, and then measured improvements following any changes I have made.
I put dd1 onto a gf/cf diet at age 2, after extensive reading on here (and elsewhere), and having done the Sunderland test which suggested it may help.
within a month (some changes were a LOT faster) she:
had started talking properly, instead of pure echolalia.
had a proper and appropriate pain response begin to develop - she had had no idea of pain before, even quite severe pain.
had improved eye contact, and more interest in us and the world around her
slept better
had better bowel movements (although this took years to improve to the point of normality)
had increased appetite, and was more willing to try new foods (again, this increase has carried on over the years - she will, at the moment, try any new food, and is interested in trying new recipes)
tbh, the list is endless. it was not an overnight change (although some elemeents were), and she continues to improve, and benefit from the diet, some 5 years on. it has, until the last 6 months or so, always been immediately obvious when she has had a diet infringement (and I don't mean the parent effect of worrying so much that she has had colours/sweetners/shit food that behaviours are misattributed, I mean actual measurable differences in how she reacts, her anxiety goes through the roof, her bowel movements are almost instantly foul again, she loses urinary continence etc)
I would say read up about it. a lot. dig through the archives here. a book I found very interesting and useful was the Marilyn Le Breton one - she has a big list of 'symptoms' which indicate whether your child would benefit from a dietary change or not - dd1 ticke dall the boxes - and see whether you want to give it a whirl.
I am fully aware that a lot of these things have no solid scientific base - I don't need that in order to see the changes in my child, ithin my home. and tbh, I have yet ot find a mainstream doctor who is actually interested in listening to anythign I have to say wrt the differences in dd1 (I have offered in the past ot put her back on a normal diet, and then have the changes documented by them, but it was declined). again, I don't need their backing, tbh, if theya re so close minded - dd1 has made massive leaps of progress, beyond what anyone ever predicted for her, and a lot of it is because the dietary changes gave her the relief from physical symptoms, and space to be able to sort herself out.
I have also used Sensory Integration OT with dd1 to great effect - again massive changes, this time overnight. I know what the literature says, and I know what I saw with dd1.