My response to this is very long, my time is very short... Let's see how I go.
There is mounting evidence that careful elimination diet absolutely helps with the symptoms of ADHD - look for an article published in the Lancet last year. My own children are on elimination diets, my child with aspergers has the most dramatic response to diet (and is the most restricted), she was previously diagnosed with ADD and medication trial did not work convincingly so it was quickly stopped. Diet alone continues to be a critical part of her life. My middle child responds to diet enough that we keep doing it, she responds less than my eldest and got many more foods back during the challenge phase, so she is much less restricted (just numbers, dairy and gluten). She has combined type ADHD and for her medication is dramatically effective, far more so than diet. So to recap I have one child for whom diet is crucial and medication did not help her attention issues (and has since been diagnosed with Aspergers). And one child for whom diet helps but medication is dramatically more effective.
My personal feeling is that for children with neurological differences like ADHD/ASD they have very very sensitive systems and are more reactive than other people to diet, chemicals in the environment, heck even the weather. So controlling those things as much as possible can help enormously (we use no cleaning chemicals, carefully selected washing powders, shampoo, etc). But for many children who truly have ADHD diet alone will not be enough.
My DD is pretty well behaved, her teachers were not complaining to us about how disruptive she was. We have always taken the most natural approach to everything that we possibly could, so medication was hard for us to come at. But after a lot of reading and research I ended up concluding that a trial was worthwhile and the results that we see in our middle child are simply indisputable. She's a little girl who deserves to be able to hear when she is spoken to, say "Yes, I'll do that!", actually do it and enjoy the success of regularly being able to do what is expected of her, her handwriting is radically improved on medication, her piano playing, her reading, her ability to look you in the eye and talk back to you... It's really quite astonishing. For us we also feared where we could see things going with her oppositional behaviours and wanted to simply not go there. And I think that a lot of that behaviour is rooted in it being too hard to even process the instructions off medication - so she will pretend she doesn't WANT to listen/comply in order to save face because she doesn't want to show that she actually CAN'T listen/comply.
Final thought - My child for whom diet makes the biggest difference was an extreme picky eater. She refused solids until 2.5yrs+ and it took us until 8-9yrs old to get her eating a reasonable range of foods (slowly, gently and respectfully working on it all the time). She lost almost ALL the "healthy" foods she had never wanted to eat in the first place and is healthier for it.
