The news has been full of reports of the INCA study, including the following conclusion on National Public Radio from the lead author, Lidy Pelsser, MSc: “64 percent of children diagnosed with ADHD are actually experiencing a hypersensitivity to food.” CHADD experts have looked at the study published in The Lancet. Without a great deal more research that supports the findings of this study, we would urge people to slow down and not jump to trying an elimination diet.
The families in the study were either put on a rigorous and closely supervised elimination diet or assigned to a control group that received instructions for a healthy diet. An alternative explanation for the results could easily be that the children in the experimental group responded well to a highly structured environment and lots of attention—both necessary for an elimination diet—and not the diet itself. Another explanation is the all-powerful placebo effect.
While this was a randomized study, the participants all knew which group they were in. This lack of blind experimental and control groups is a major research design flaw. The placebo effect is usually controlled by making sure all participants are blind to the intervention they are receiving. For instance, an experimental group might get the elimination diet and the control group might get a bogus elimination diet which eliminates only foods unlikely to make a difference. Then the children in both groups would receive the same amounts of structure and adult involvement. That did not happen in this study. Conclusions about hypersensitivity to food and ADHD cannot be made on the face of this single study, and certainly not when the groups were aware of the interventions.
Years of research on diet and ADHD have concluded that a very small percentage of children with ADHD who also have food hypersensitivities may do well with a controlled diet. So if you know or suspect your child has food hypersensitivities, then you may want to try an elimination diet with good medical supervision. But for the vast majority of people with ADHD, there is not yet evidence that this will make a difference.
Ruth Hughes, PhD
CHADD Interim CEO