Understand that that guy's just trying to sell snake oil. Pay more attention to
your doctor.
I was diagnosed in 1977, and have been on three different meds. While there may be something to [not] eating certain things, it's going to likely be very idiosyncratic to you personally. That's for you to figure out on your own, though you're of course welcome to take that guy's ideas as a starting point. I'd just stop short of doing anything which puts money in his pocket until you're certain he actually has a clue.
Having or putting "Dr." in front of his name isn't enough, 'cause it doesn't mean
shit. He might be a PhD in basket weaving, if that much. I'd want to check his credentials before I'd grant him more cred than a trash man.
ADD sucks, no doubt about it at all.
OTOH, there are
much worse things you can have, so don't feel
too sorry for yourself. Learn to handle it, instead.