Hi Lauren,
In the 70's there was a doctor named Benjamin Feingold who determined that sugar, preservatives, food colorings and additives contributed to the issues of a child with ADHD or ADD. Eileen Bailey wrote an article about this explaining that when the report was new, some folks were skeptical, but apparently there is a link that you can read about here.
There is also a good video you can watch here about the impact of diet on ADHD kids.
Take care and stay in touch. Let us know how you and your son are doing!Vicki M