This theory has long been advocated by such notable groups as The Feingold Association (http://www.feingold.org/). However, their studies have been limited to smaller groups and anecdotal evidence. While their findings have been compelling, medical doctors and adversarial attacks by the processed food industry quashed overall acceptance of dietary restriction. The NIMH give only limited credence to the theory.
Feingold and other advocates of the restrictive diet have suggested that the introduction of food additives can affect the human immune system sometimes causing reactions like hyperactivity, inattention, and even eczema, asthma and gastrointestinal problems. In light of research about food colorings and hyperactivity, the British have taken steps to eliminate certain preservatives and food dyes from their food supply.
The study published in the Lancet was funded by Foundation of Child and Behaviour, Foundation Nuts Ohra, Foundation for Children’s Welfare Stamps Netherlands, and the KF Hein Foundation. The researchers placed 100 children from Belgium and the Netherlands into two groups: one that received the restrictive diet and the other that only received advice on healthy eating habits. The group that received only advice on healthy eating was the control group. All of the children had been diagnosed with ADHD and were between the ages of 4 and 8.
The children were placed on the restrictive diet for a period of five weeks. They were allowed to eat only rice, meat, vegetables, pears and water. Later, the children were allowed to additionally consume potatoes, fruits and wheat. The researchers assessed ADHD symptoms during this period.
Over the course of the next four weeks, researchers reintroduced processed foods into the restricted diet group. The researchers selected foods that were previously considered to negatively affect body or immune responses.
Nine children withdrew from the restrictive diet group. Attrition in all studies is common. Of the forty-one children who completed the restrictive diet program, 78 percent had a reduction in their ADHD symptoms, compared with no improvement in the controls. Assessment was performed using an ADHD symptom scale that ranges from 0 to 72 points. Higher scores in the scale indicate more severe symptoms. The average reduction was 24 points, a significant reduction.
Thirty children who demonstrated decreased ADHD symptoms resulting from the restrictive diet were selected for reintroduction of foods outside the restrictive diet. This was deemed the ‘challenge test.’ Nineteen of the thirty children had a relapse in symptoms on the challenge test. Sensitivity to foods thought to produce high immune response didn’t seem to produce any greater negative effects than foods thought to produce lower immune response.
Limitations of the study include restriction to ADHD; it cannot be discerned whether it would apply to ADD. Secondly, not all children responded to the restrictive diet. Of those who did respond, responses to foods seemed to be equal no matter what processed food was introduced back into the diet. Additionally, under this research design, it was not possible to have a blind control; parents knew what group their child was in. If they also knew the expected outcome of the study, it might have influenced the outcome.
On the practical side, the restrictive diet is very difficult to follow consistently. However, if your child seems to respond well when you remove certain processed foods, this research seems to support your observation although the certainty about diet and ADHD symptoms has not been clearly established by this study.