Does sugar cause hyperactivity?

Short answer: No

Following a review of 23 studies, a 1996 report published in the Journal of the American Medical Association concluded that sugar "does not affect the behavior or cognitive performance of children."

The age-old myth that kids misbehave when they eat large amounts of candy, cookies, and other junk food, could be related to the type of events where these foods are typically served. For example, kids are more wound-up at birthday parties and during Halloween when sweet treats tend to flow freely.