The idea that some children’s ADHD symptoms are caused by dietary factors has been around for many years. In fact, the possibility that diet exerts a significant influence on ADHD symptoms was proposed over 3 decades ago by Dr. Ben Feingold, a pediatrician who suggested that eliminating a variety of artificial food colors (AFCs), naturally occurring salicylates (salicylates are chemicals that occur naturally in many fruits and vegetables), artificial flavors, and particular preservatives could substantially reduce ADHD symptoms in many children.
Controlled trials of the Feingold Diet first appeared in the literature during the 1970s, and a meta-analysis of relevant research published in 2004 – see www.helpforadd.com/2005/april.htm – concluded that children’s behavior showed a statistically significant improvement when AFCs were eliminated from their diet. The size of the improvement was relatively modest – about a third to a half as large as the improvement typically associated with medication treatment for ADHD. (If you would like to learn more about the Feingold Diet, you can do so at www.feingold.org.
Results from a more recent meta-analysis on the association between ADHD and diet concluded that roughly one-third of children diagnosed with ADHD may respond to diets that restrict access to certain foods.[Nigg et al., (2012). Meta-Analysis of Attention-Deficit/Hyperactivity Disorder or Attention-Deficit/Hyperactivity Disorder Symptoms, Restriction Diet, and Synthetic Food Color Additives. Journal of the American Academy of Child & Adolescent Psychiatry, 51, 86-97] The authors noted, however, that the impact of diet on ADHD symptoms is likely to be substantially smaller than that produced by medication.
Results from a study published in 2011, however, suggests that dietary interventions for ADHD may be more powerful than previously thought [Pelsser et al., (2011). Effects of a restricted elimination diet on the behaviour of children with attention-deficit hyperactivity disorder (INCA study): a randomised controlled trial. Lancet, 377, 494-503. I missed this study when it was published and only recently became aware of the findings. Because this is potentially an extremely important investigation I am pleased to summarize it for you below.
The Impact of Nutrition on Children with ADHD (INCA) Study
The INCA study was conducted in the Netherlands and Belgium and involved 100 4- to 8-year old children (86 boys) diagnosed with any subtype of ADHD; 47 also had a diagnosis of Oppositional Defiant Disorder (ODD). Diagnoses were established via a structured psychiatric interview administered by an experienced pediatrician. One hundred eighty-nine children were initially screened for the study. Fifty-five were excluded because they did not meet criteria for ADHD and another 27 were excluded because families were either insufficiently motivated to enroll or experiencing circumstances that were likely to interfere with completing the study. Six children taking medication were also excluded.
Children were randomly assigned to a 5-week Restricted Elimination Diet(RED)or to a ‘healthy diet’. The former was a highly restricted diet and included only a few hypo-allergenic foods – rice, turkey, a range of vegetables (lettuce, carrots, cauliflower, cabbage, beets), pears and water; this is referred to as the ‘few foods’ diet.
During the first week, children were permitted some additional foods so that the diet was not more limited than it needed to be. However, if significant behavior changes were not observed by parents after one week, these additional foods were gradually removed and children were limited to the ‘few foods’ diet. Calcium was supplemented via adding it to a daily non-dairy rice drink so that children were not at risk for nutritional deficiencies.
Parents of children assigned to the ‘healthy diet’ group were given information on healthy eating for children, but were not required to restrict the foods their child ate. Both groups kept careful records of children’s food intake during the trial.
After 5 weeks, children in RED who responded positively – defined as a 40% reduction in ADHD symptoms – proceeded with a 4-week double-blind food challenge phase. During the challenge phase, two groups of additional foods were introduced for successive 2-week periods. These foods differed in their propensity to induce an allergic response and parents did not know when children were receiving hyper- or hypo-allergenic foods. The food challenge was implemented to see whether introducing new foods led to a return of ADHD symptoms in children who responded to RED, and, whether this depended on the types of foods introduced.
Measures – The main outcomes collected were ratings of ADHD symptoms completed by parents and teachers using the ADHD Rating Scale; ratings of oppositional behavior were also obtained. These ratings were collected at baseline, 5 weeks after the diet began, and then again after each 2-week food challenge.
Keeping parents and teachers ‘blind’ to whether children were in the RED or Healthy Diet group was not possible as parents prepare food for their children and teachers see what children bring for lunch. However, the pediatrician completing ratings was blind to children’s condition. Other than having ‘blind’ observers in the classroom to rate children’s behavior, which unfortunately was not part of the study, this as good as one can do.
Forty-one of 50 children assigned to RED completed the 5-week diet. Thirty-two (78%) were considered ‘responders’ in that parent ratings showed at least a 40% reduction in ADHD symptoms. This is a clinically meaningful reduction.
On average, parent ratings of inattentive symptoms declined by 53% for children in the RED group; ratings of hyperactive impulsive symptoms declined by an average of 54%. These average reductions are based on all 41 children assigned to RED, not just the 32 considered ‘responders’. Results based on teacher and pediatrician ratings were highly similar. And, comparable results were obtained for ratings of oppositional behavior.
In contrast to the substantial symptom declines seen in the majority of children on RED, symptom ratings for children in the Healthy Diet group remained essentially the same for all 3 raters.
What happened when children who responded to RED had new foods added to their diet? Approximately 60% showed a significant increase in ADHD symptoms and this did not depend on whether the foods introduced were more or less likely to trigger an allergic response. On average, symptoms did not return all the way to baseline levels but there was a statistically significant and clinically meaningful increase.
This is an important study. What is especially noteworthy is that the majority of children with ADHD who were placed on the few foods diet showed a 40% reduction in ADHD symptom ratings; their oppositional behavior improved as well. In fact, the magnitude of the benefits obtained were larger, on average, than what is commonly found with medication. These results suggest that a restricted elimination diet can have substantial benefits for many children with ADHD, and not just for a small minority of diagnosed children. Although results from this study indicate a potentially larger effect of a restricted elimination diet on ADHD symptoms than has been reported in previous work, the results are largely consistent with other studies that have examined this issue in a similar way.
Based on this finding, the authors recommend that all children should be considered for dietary intervention for ADHD, provided that parents can to follow a restricted elimination diet for at least 5 weeks so that its value can be determined and that close supervision is available.
Because these results are so striking, it is important to place them in an appropriate context. First, the study included only children between 4 and 8. This age range was chosen because the authors felt it would be easier for parents of younger children to maintain their child on the diet. Whether the diet would be equally effective with older children/adolscents is unknown. And, it would likely be more difficult to keep older children on such a restricted diet for an extended period.
Second, even with younger children, it is unclear how long such a diet could be maintained and how long the benefits would persist. A majority of children ‘relapsed’ when new foods were added to their diet and trying to keep children on the ‘few foods’ diet over a truly extended period could be extremely difficult. Even if this were done, it is possible that the benefits reported here would not last.
Third, parent and teachers could not be kept blind to children’s condition, i.e., RED vs. Healthy Diet. Thus, expectancy effects may have contributed to the findings. Although the pediatrician was blind, her ratings were based on observations of the child and on information provided by parents. Thus, ratings of the ‘blind’ pediatrician were at least partially influenced by ‘unblinded’ parents.
It would have been ideal to have ‘blind’ raters observe children at school and to collect objective measures of attention – perhaps with a computerized test – but this was not done. I think this is an important limitation as if similar findings had been obtained from a truly ‘blind’ observer, or from an objective assessment that would not be affected by ‘expectancy effects’, the findings would be very difficult to dispute.
Fourth, the mechanism by which the elimination diet ‘worked’ in children who responded remains unclear. As noted above, not all children relapsed during the food challenge phase and relapse did not depend on whether the foods added were more or less likely to trigger an allergic response. Thus, the underlying mechanism of food sensitivity in ADHD is suggested to be non-allergic, although what that mechanism is remains unknown.
Although these are important limitations, the results of this study are striking and suggest that there may be a much larger role for dietary interventions than has been previously assumed. Certainly, the findings highlight the value of additional research on dietary interventions that begin to address the limitations noted above.
P.S. Results of this study were so striking that at least one leading ADHD expert raised a number of concerns about the study, including concerns about related to scientific misconduct. You can find an interesting letter written by the study authors in response to these concerns at www.adhdenvoeding.nl/cms/wp-content/uploads/2012/12/INCA-Reply-Letter-Prof-barkley.pdf”> The letter is is a bit technical but nonetheless makes for interesting reading.
Thanks again for your ongoing interest in the newsletter. I hope you enjoyed the above article and found it to be useful to you. If you haven’t yet tried DefiniPoint’s online system for obtaining behavior rating scale date, I encourage to become familiar with the benefits of this new system by watching a 3-minute video on their program.
David Rabiner, Ph.D.
Dept. of Psychology & Neuroscience
Durham, NC 27708