Some doctors attribute ADHD, particularly the inattentive sort, to actually be a manifestation of general allergic reactions which really just makes people tired, and triggers symptoms that would classify a person as having ADHD according to the DSM (Remember, the DSM generally makes no distinctions as to what causes a condition, it only diagnoses it.) They often try to treat the allergies first, which is generally a good start.

I have both ADHD and a mild latex allergy. Ironically, the latex allergy makes eating almost any fruit shitty ( http://en.wikipedia.org/wiki/Oral_allergy_syndrome#Cross_rea... )

However, my diet has definitely kept clear of most of these foods when possible for a long time now (although I really do love avocados), and even did the fatty fish thing for a while, but symptoms haven't changed for me.