I think one issue is that until very recently-there was little or no interest or concern regarding ADHD in adults. So (like studies on poly people and GLBT peeps) there is very little conclusive information for that.
I can't speak to the whole food color blah blah blah. It's not something I deal with.
I can speak to the fact that hyperactivity comes in two forms-one is physical hyperactivity that we all think of when we hear the word. But the other is in the thought process/talking aspect.
Females tend to be more likely to be "hyper" in the second form than the first.
Also, there are several types of ADHD that don't have hyperactivity at all.
My boyfriend is ADD. He's not hyper by any stretch of the word.
Regarding adults; my mom (60s), myself (38), husband (41), boyfriend (37), ex brother in law (38), my daughter (21), sister (19) are all diagnosed.
There's an OBVIOUS difference in our thought processes, memory, attention span-compared to my sister who is 37 and not ADD for example. So much of an obvious difference-that it would be darn near impossible NOT to notice!
Interestingly enough-the difference isn't in 'hyperactivity' as much as distractedness, impulsivity, memory, attention span limitations.
Too many people think that ADHD's biggest sign is hyperactivity. It's really not.
I will see if I can find some good links for you. (It was me who suggested Midnightsun post by the way-she's an ADHD coach and runs the local CHADD group here)
But-I have a lot of homework to do, so it may be a bit. Trying to finish out the semester.