I'm trying to play devils advocate, and all I can think of is that maybe the super-strict limits that had to be enforced had a behavioral effect? Maybe the kids were shook up enough that they felt like they HAD to behave? I doubt it, what else could it be - besides food reactions?
I do believe that food alone can have profound effects. I was breast-feeding when we were trying to sort out DS's food allergies. I ended up being on a severely restricted diet for almost a year. Similar to the study, I ate turkey, chicken and pork, fruits and vegetables and various grains (OK -- I cheated and had wheat occasionally). When I finished breast-feeding and added foods back into my diet, I noticed that certain foods affected my mood and energy level. Wheat saps my energy. Anything with flax seeds, makes me have severe mood swings. I won't bore you with more details but you get the idea.
The hard part is following a restricted diet in the first place. With food sensitivities, as opposed to true food allergies, it's hard because you are asking a kid to abstain from eating things that they have always been able to eat. Once you get through the restricted part, I agree with Kerry that if the kid can make the connection between food and how they feel, they will advocate for themselves.
