ArticlesEffects of a restricted elimination diet on the behaviour of children with attention-deficit hyperactivity disorder (INCA study): a randomised controlled trial
Introduction
Attention-deficit hyperactivity disorder (ADHD) affects 5% of children worldwide and is characterised by excessive and impairing inattentive, hyperactive, and impulsive behaviour.1 Genetic and environmental factors are involved,2 and ADHD is often accompanied by oppositional defiant disorder.3 Children with ADHD and comorbid oppositional defiant disorder are difficult for parents, guardians, and teachers to handle, give rise to substantial parenting stress, and have a worse prognosis for adverse outcomes (ie, an increased risk of developing conduct disorder and antisocial personality disorder) than have children without comorbidity.4 At present, ADHD is treated with psychoeducation, parent training, child behavioural interventions, and drugs,5 but follow-up studies have reported limited long-term effects of multimodal treatment.6, 7
One of the risk factors for ADHD that could be targeted for intervention is food.8 Reports of adverse physical reactions to foods (eg, eczema, asthma, and gastrointestinal problems) that affect various organ systems9 have led to the suggestion that foods might also affect the brain, resulting in adverse behavioural effects.10 Colourings and preservatives might have some effect on the behaviour of children with or without ADHD, but additives do not cause ADHD.2, 5, 11, 12 An individually constructed restricted elimination diet, which consists of some hypoallergenic foods, might be effective for treatment of ADHD.8, 11 The rationale of this diet for children with ADHD is to investigate whether ADHD is triggered by foods—ie, to identify a hypersensitivity reaction to foods. In a small randomised controlled trial that investigated the effects of a restricted elimination diet,13 we reported statistically significant and clinically relevant effects on ADHD and oppositional defiant disorder.
In children with ADHD that is triggered by foods, ADHD meets the criteria of hypersensitivity according to allergy nomenclature.14 Accordingly, we postulated that ADHD might be an allergic or non-allergic hypersensitivity disorder in some children.15 IgE is implicated in typical food allergies. In reactions to food that are not mediated by IgE, assessment of IgG levels might be useful,16 and IgG blood tests are offered—especially in complementary care17—with the aim of establishing a relation between foods and ADHD. According to this theory, eating foods that induce high IgG levels would lead to a substantial behavioural relapse whereas eating those that induce low IgG levels would not. However, there is no evidence for the effectiveness of these tests.18
The primary aim of the Impact of Nutrition on Children with ADHD (INCA) study was to investigate the effects of a restricted elimination diet on behaviour in children with ADHD. The secondary aim was to differentiate between non-allergic and allergic mechanisms in food-induced ADHD.
Section snippets
Participants
Children were recruited at medical health centres and through media announcements in the Netherlands and Belgium. Interested parents or guardians (hereafter called parents) were provided with verbal and written information about the study. Eligible children were assessed for ADHD and comorbid disorders by a senior paediatrician (JT) using a structured psychiatric interview (SPI). Children were included if they had been diagnosed with ADHD of any subtype.1 Further inclusion criteria were
Results
Between Nov 4, 2008, and Sept 29, 2009, 100 children were enrolled and randomly assigned to the control group (n=50) or the diet group (n=50; figure 1). Most children were boys and the mean age was 6·9 years (SD 1·3; table 2). Of the 41 children in the diet group who completed the first phase, the diet of 17 was restricted to the few-foods diet only.
Table 3 and figure 2 show the ARS results from the first phase. Of the 41 (82%) of 50 children in the diet group who completed the first phase,
Discussion
In the INCA study, the restricted elimination diet had a significant beneficial effect on ADHD symptoms in 32 (64%) of 50 children, and reintroducing foods led to a significant behavioural relapse in clinical responders. Blood tests assessing IgG levels against foods did not predict which foods might have a deleterious behavioural effect. The effect of the diet was consistent and had a similar effect in reducing both ADHD and oppositional defiant disorder symptoms. Because of the worse
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