When I was around 8 or so, (well before that) I had major behavioral problems -- later diagnosed to be ADHD.
Before that, my parents had me submitted for CAT scans, normal allergy tests, etc. This food allergy test (done by a bunch of quacks in my opinion) confirmed that I was severely allergic to brewers yeast as well as having allergies to chocolate, wheat and numerous other things.
I was 8, yet couldn't eat normal bread. Had to use that rice bread crap for school lunches -- they didn't have all these alternative breads back then. Eventually, I quit that special diet and nothing changed. Was eventually diagnosed with ADD (which really wasn't widely acknowledged at the time) and later I was subgrouped into the ADHD category.
Since then, of course, I quit taking the drugs and am basically normal although sometimes symptomatic you wouldn't know I had it unless I told you
