Some effects on brain electrical activity have been documented, and reactive hypoglycemia following big jolts of sugary foods may account for behavioral changes seen in some ADHD children.
But studies linking sugar consumption to ADHD have also been compromised by methodological problems. For example, one trial gave children sugar or placebo at breakfast with a high-carbohydrate cereal, which may have contributed to subsequent reactions to the sugar. Millichap and Yee cited a separate study that demonstrated when children ate a protein meal before or simultaneously with sugar, no hyperactivity reaction occurred.
Still, the researchers conceded, the notion that sugar exacerbates ADHD has become so entrenched it may not matter whether it's true or not.
"No controlled study or physician counsel is likely to change this perception. Parents will continue to restrict the allowance of candy for their hyperactive child at Halloween in the belief that this will curb the level of exuberant activity, an example of the Hawthorne effect. The specific type of therapy or discipline may be less important than the attention provided by the treatment," Millichap and Yee wrote.
They also reviewed studies exploring the potential roles of zinc and iron deficiency in ADHD. The upshot is that there is currently little indication that such deficiencies explain more than a small minority of ADHD cases. Children with confirmed deficiencies should receive supplements or appropriate dietary adjustments regardless of their ADHD status.
They were more impressed with the literature on polyunsaturated fatty acid supplements, especially the 2005 Oxford-Durham study.
In that trial, several ADHD symptoms were significantly improved in children receiving omega-3 and omega-6 fatty acid supplements, "an effect duplicated in other...supplement trials," Millichap and Yee wrote.
They acknowledged that not all studies have confirmed the result, and recent studies have used too many different methodologies to yield firm conclusions. Nevertheless, they indicated that they now recommend it to parents of their patients, though not as the sole treatment approach.
"In almost all cases, for treatment to be managed effectively, medication is also required," they wrote. "The beneficial effects of omega-3 and omega-6 supplements are not clearly demonstrated."
"Supplemental diet therapy is simple, relatively inexpensive, and more acceptable to patient and parent," Millichap and Yee concluded. "Public education regarding a healthy diet pattern and lifestyle to prevent or control ADHD may have greater long-term success."
They suggested that diet-based interventions in ADHD are most appropriate when children suffer medication reactions or treatment failure, parents or children want to try dietary modifications or mineral deficiencies are evident.