What role does diet play in ADHD? This has been a highly debated
question for years and a clear answer has remained elusive.
Several years ago, in response to findings from a randomized-controlled
trial on the impact of food additives on children's behavior, the American
Academy of Pediatrics (AAP) issued a statement that "For the child without
a medical, emotional, or environmental etiology of ADHD behaviors, a trial
of a preservative-free, food coloring free diet is a reasonable intervention."
This was an important acknowledgment by the AAP that diet contributes to ADHD
behaviors in some children, and that modifying children's diet may be helpful.
In a prior issue of Attention Research Update - see http://www.helpforadd.com/2010/september.htm
- I reviewed another study that supports this conclusion.
Despite evidence that diet contributes to ADHD behaviors in some children
it remains unclear whether this applies to a significant percentage of children
with ADHD or to a relatively small minority. A recent study published in
the British journal The Lancet provides new data on this issue and raises
the possibility that diet may be a contributing factor in many children with
ADHD [Pelsser et al. (2011). Effects of a restricted elimination diet on
the behavior of children with attention-deficit hyperactivity disorder (NICA
study): a randomized controlled trial. The Lancet, 377
The study was conducted in Belgium and the Netherlands. Participants
were 100 4-8-year old children (approximately 85% males) diagnosed with
ADHD. Children were randomly assigned to a diet group or a control
group. The diet tested was the 'few foods' diet which largely limits food
intake to rice, meat, vegetables, pears and water. Parents of children
assigned to the control condition were given advice about a healthy diet
for their child, but no effort was made to systematically alter food intake
for these children.
At baseline, and five weeks after children started the diet, parents, teachers,
and a pediatrician completed ratings of children's ADHD symptoms and oppositional
behavior using standardized behavior rating scales. Immunoglobin E (IgE)
blood levels were also measured to learn whether they showed any association
with behavioral response to the diet (Note - IgE is implicated in typical
food allergies and reduced IgE levels in children who responded to the diet
would be expected if their ADHD symptoms were related to allergic reactions
It is important to note that parents and teachers could not be kept 'blind'
to whether each child was in the diet or control group because considerable
effort was required to insure children adhered to the few foods diet.
Pediatricians who examined the child were not aware, however, did remain
blind to each child's condition.
- Phase 2
Phase 2 of the study was restricted to children in the diet group who showed
significant reductions in ADHD symptoms during the five week dietary intervention.
These children had 2 different types of foods added to their diet - those
with high levels of immunoglobin G (IgG) and those with low levels of immunoglobin
G (IlG). These food types were selected to test whether foods that
induce high levels of IgG antibodies are linked to ADHD symptoms.
Diet responders received the IgG or IlG foods for two weeks each; after
the initial two-week cycle the first food type was removed from the child's
diet and the other food type was introduced for two weeks. Behavioral
ratings were obtained at the end of each two-week period to test whether either
food type was associated with a return of ADHD symptoms.
For this portion of the study, neither parents or teachers were aware of
which food type was introduced first and which was introduced second.
They were all aware, however, that new foods had been added to their child's
Question 1 - Did children placed on the 'few foods' diet show a significant
reduction in ADHD symptoms?
Thirty-two of 50 (64%) children put on the few foods diet showed a reduction
of at least 40% in ratings of ADHD symptoms. This was true for 'unblinded'
ratings of parents and teachers as well as the 'blind' ratings made by the
pediatrician. Similar positive results were obtained for ratings of
oppositional behavior. In all cases, the reductions reported for the
diet group were substantially larger than for the control group, where reports
of children's symptoms remained relatively stable. No association
was found between IgE levels and children's response to the diet.
Question 2 - Did introducing new foods lead to an exacerabtion of symptoms
in children who had responded positively to the few foods diet?
Introducing new foods that were either low or high in immunoglobin G resulted
in a significant increased in ADHD symptoms among children who had shown
a positive response to the diet. Symptom ratings did not fully return
to what they had been at baseline, but the increase following the introduction
of new foods represented more than 50% of the decline that was recorded
during phase 1. NO differences in symptom increase was found for the
IgG or IlG foods.
- Summary and Implications
These are impressive findings in that nearly two-thirds of a representative
sample of young children with ADHD showed a substantial reduction in ADHD
symptoms when placed on the 'few foods' diet. In fact, the authors
conclude their study by suggesting that "...dietary intervention should be
considered in all children with ADHD, provided parents are willing to follow
a diagnostic restricted elimination diet for a 5-week period, and provided
expert supervision is available."
This is a strong statement and it is important to carefully evaluate whether
it is fully supported by the study results.
Here is my concern with the study. In the first phase, because parents
and teachers were aware of which children were on the diet, it is possible
that their ratings were influenced by this knowledge. This is a limitation
the authors readily acknowledge. Although the 'blind' pediatrician
made similar ratings, these ratings were based not just on the pediatrician's
observations of the child during the exam, but also on information provided
by the parents. Thus, pediatrician ratings were likely influenced by
the potentially biased parent reports. In my view, this is a plausible
alternative explanation for the results obtained.
What about the fact that introducing new foods to children who responded
positively to the diet led to a significant increase in their symptoms?
Doesn't this show that ADHD symptoms were exacerbated when foods not part
of the 'few foods' diet were consumed?
Possibly, but because parents knew that new foods were being introduced,
their ratings may have been biased by expectations that deviating from the
diet would contribute to a return of their child's symptoms. This
would be a poor argument if results conformed to the expected pattern, i.e.,
an increase when IgG foods were introduced by not when IlG foods were introduced,
but this is not what was found. Instead, similar increases followed
the introduction of both food types, which would be plausible if expectations
were influencing parents' ratings.
Given that 'blinding' parents was not possible, how could the alternative
explanations suggested above been ruled out? While completely ruling
out these alternatives is not possible without full blinding, it would have
been helpful if measures of child functioning less susceptible to ratings
bias were obtained. For example, an objective computerized test of
attention and impulsivity would not be subject to such bias. If results
on this measure aligned with the rating results, it would permit greater
confidence in the validity of the rating data. School-base observations
of children's behavior made by 'blind' observers would also have been a strong
addition, although I recognize the difficulty involved in obtaining such
Other issues to note are that maintaining children on such a strict diet
is challenging; in fact the authors deliberately selected young children
so that compliance with the diet could be maximized. Whether this intervention
could be viably implemented with older children and adolescents is unclear.
Also unclear is how long even young children could persist on a restricted
diet beyond the 5 weeks examined in this study.
These concerns not withstanding, this was a well done study and I hope
my comments don't come across as overly critical. As with any study,
however, it is important to consider plausible alternative explanations
for the findings, and those suggested above seem plausible to me.
Having said this, it seems unlikely that the strong positive response found
in nearly two-thirds of children placed on the diet could be fully explained
by these issues and trying such a diet - under appropriate medical supervision
- is an option that some parents may wish to consider.
If this approach is tried it would seem important to adhere to the suggestion
made by Dr. Jaswinder Kaur Ghuman in a commentary that accompanied the study's
publication in The Lancet. In this commentary, Dr. Ghuman noted that
"..."stringent elimination diet should not continue for more than five weeks
without obvious benefit because of the time, effort, and resources required
to implement the restricted diet and because long-term effects of dietary
elimination on the child's nutritional status are not known."