Strangers with Marshmallow Recipes

I met an amazing woman at the grocery store today. She was looking for healthy sandwich bread and I directed her to the new bread with no artificial additives or preservatives I found. We then began discussing the evils or corn syrup which then led to her son and the Feingold diet. Her son is grown now with children of his own, but she believes the Feingold Diet saved his life. For those of you unfamiliar with this diet, it eliminates artificial colors, flavors, preservatives, and salicylates found in healthy foods such as apples, berries, grapes, citrus, etc. She said her hyperactive, depressed, suicidal thought having 6 year old became an unbelievably well adjusted person on this diet. It was an amazing story. She stuck strictly to the diet for 4 years before introducing any offending foods.
I've heard the Feingold diet can help children with allergies and the irritability that comes with them. My son is sometimes hyperactive, but not depressed or suicidal (whew!) But I hesitate taking anything else from him. His diet is already limited by his food allergies- do I take away berries and apples too? He really likes them, and they could potentially be making him feel worse. I'm not sure what's right or wrong. But I do know the amazing woman I met has a homemade marshmallow recipe and I am definitely gonna try to make some. Then I can buy preservative free crisped rice and go to town!