I have friends with children whose behaviours improved drastically when diet was modified. In some cases, all the ADHD-like behaviours either stopped or were greatly reduced. Of course this doesn't mean it will be the same for others. But with these friends they too discovered they couldn't handle things like amines or salicylates or whatever and once they eliminated stuff from their diet, their own behaviours/health/etc improved exponentially.
I think dietary changes should be a must for lots of people, not just ADHD, autism, and so on. My friend has bad asthma, nasal polyps, migraines and all this other stuff. Once she went on a Failsafe diet, all those things disappeared and came back when she reintroduced the foods during challenges. She lived with all those problems for years which really took their toll as her sleep was very poor due to coughing, blocked sinuses, headaches and so on. Now she has none of those and her quality of life is of course much better.
My siblings have been diagnosed with IBS but all their colonoscopies, blood tests and gastroscopies have come back clear. They're now about to start the elimination diets and I'm so pleased because I'm certain it is due to something they're eating. Everyone we know who has tried an elimination diet have all said they wished they'd done it sooner, and spared themselves a lot of pain and misery.
