Here are 3 studies that explain the effects sugar can have on ADHD...

1. Effects of Sugar on Aggressive and Inattentive Behavior in Children With Attention Deficit Disorder With Hyperactivity and Normal Children

"Although the children with attention deficit disorder with hyperactivity were significantly more aggressive than the control subjects, there were no significant effects of sugar or either placebo on the aggressive behavior of either group. However, inattention, as measured by a continuous performance task, increased only in the attention deficit disorder with hyperactivity group following sugar, but not saccharin or aspartame."

Official Journal of the American Academy of Pediatrics - http://pediatrics.aappublications.org/cgi/content/abstract/8...

2. Nutrition in the Treatment of Attention-Deficit Hyperactivity Disorder: A Neglected but Important Aspect

"Attention-deficit hyperactivity disorder (ADHD) is multidetermined and complex, requiring a multifaceted treatment approach. Nutritional management is one aspect that has been relatively neglected to date. Nutritional factors such as food additives, refined sugars, food sensitivities/allergies, and fatty acid deficiencies have all been linked to ADHD. There is increasing evidence that many children with behavioral problems are sensitive to one or more food components that can negatively impact their behavior. Individual response is an important factor for determining the proper approach in treating children with ADHD. In general, diet modification plays a major role in the management of ADHD and should be considered as part of the treatment protocol."

Applied Psychophysiology and Biofeedback - http://www.springerlink.com/content/vr40331382376623/

3. Blunted catecholamine responses after glucose ingestion in children with attention deficit disorder.

"Eating simple sugars has been suggested as having adverse behavioral and cognitive effects in children with attention deficit disorder (ADD), but a physiologic mechanism has not been established. To address this issue, metabolic, hormonal, and cognitive responses to a standard oral glucose load (1.75 g/kg) were compared in 17 children with ADD and 11 control children. Baseline and oral glucose-stimulated plasma glucose and insulin levels were similar in both groups, including the nadir glucose level 3-5 h after oral glucose (3.5 +/- 0.2 mmol/L in ADD and 3.3 +/- 0.2 mmol/L in control children). The late glucose fall stimulated a rise in plasma epinephrine that was nearly 50% lower in ADD than in control children (1212 +/- 202 pmol/L versus 2228 +/- 436 pmol/L, p < 0.02). Plasma norepinephrine levels were also lower in ADD than in control children, whereas growth hormone and glucagon concentrations did not differ between the groups. Matching test scores were lower and reaction times faster in ADD than in control children before and after oral glucose, and both groups showed a deterioration on the continuous performance test in association with the late fall in glucose and rise in epinephrine. These data suggest that children with ADD have a general impairment of sympathetic activation involving adrenomedullary as well as well as central catecholamine regulation."

Department of Pediatrics, Yale University School of Medicine - http://www.ncbi.nlm.nih.gov/pubmed/8559606