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Attention-deficit hyperactivity disorder (ADHD), characterized by problems in attention, impulse control and activity regulation (American Psychiatric Association, 2000), is one of the most common psychiatric disorders, with a strong genetic disposition (Faraone & Mick, 2010). Both biological as well as psychosocial environmental factors are related to ADHD, including prenatal maternal smoking, prematurity, low birth weight, foetal distress, foster placing and disturbed parent–child relationships (Banerjee, Middleton & Faraone, 2007; Biederman & Faraone, 2005; Deault, 2010). An important, albeit controversial, environmental factor that may trigger ADHD is food (Arnold, 1999). Research investigating the effects of additives like colourings and preservatives on ADHD, has shown that although additives may have some effects on the behaviour of all children [effect size (ES) 0.3], additives do not cause ADHD (McCann et al., 2007). Conversely, recent research investigating the effects of a restricted elimination diet (RED), that is, eliminating many kinds of foods from the child's diet, has shown statistically significant and clinically relevant results, with ES on the ADHD DSM-IV Rating Scale varying from 1.7 according to the open teacher measurements to 2.0 according to the blinded paediatrician measurements (Pelsser et al., 2011). These results confirm the outcomes of seven previous randomized controlled trials, investigating the effects of an RED on ADHD, with an overall ES of 1.6 (Pelsser et al., 2011).
One could argue that the children's behavioural changes might be due to concomitant improvement of parental behavioural strategies, caused by the strict parental supervision necessary to comply with the RED. Research has shown that ADHD is associated with disruptive parent–child relationships and poor parenting structure (Foley, 2011; Harpin, 2005; Pressman et al., 2006; Verhoeven, Junger, Aken van, Devokić & Aken van, 2010), even more when children are suffering from comorbid oppositional defiant disorder (ODD; Deault, 2010). Conversely, consistent parenting and positive parent–child interactions are associated with improvements of child behaviour (Kaminski, Valle, Filene & Boyle, 2008). This suggests the possibility that behavioural improvements assessed in the RED trials might be mediated by the strict parenting structure necessary to follow the RED, rather than be a direct result of the diet.
The present pilot study uses a subsample of the Impact of Nutrition on Children with ADHD (INCA) study and investigated whether the effects of an RED on ADHD and ODD symptoms as previously reported (Pelsser et al., 2011), can be explained by changes in family structure during the intervention. A group of no-ADHD control children was included as a comparison group, to investigate changes in family structure over time. Our study is the first study investigating the effects of following an RED on parenting abilities.
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In both the ADHD control group and the no-ADHD control group two families left the study prematurely and one family did not complete the second FES-questionnaire. None of the families in the ADHD RED group left the trial. Most FES questionnaires were completed by the mother (43/47), and most children were boys (38/47). The FES was completed twice for each child, at start and at and of the trial, with a total number of 94 observations. No significant differences regarding age, family size, number of siblings and single parent families were found between the ADHD groups and No-ADHD control group (see Table 1). In the ADHD group 11/24 children (46%) were also diagnosed with comorbid ODD (6/11 children in de ADHD RED group, 5/13 in the ADHD control group). In the no-ADHD control group one child met the criteria for ODD, none of them meeting the criteria for ADHD.
Table 1. Baseline characteristics of study participants
| ||ADHD RED n = 11||ADHD control n = 13||No-ADHD control n = 23||p-value Fisher exact|
|Boys||10 (91%)||10 (77%)||18 (78%)||0.708|
|Age in years (mean (SD))||7.7 (0.9)||7.2 (1.2)||6.8 (1.4)||0.115a,b|
|Step/single parent family||0.1 (0%)||1 (8%)||2 (9%)||1.000|
|FES completed by mother||11 (100%)||11 (85%)||21 (91%)||0.668|
|Family size, number of siblings|| || || ||0.073b|
|Only child||0 (0%)||3 (23%)||0 (0%)||0.028c|
|1 sibling||5 (45%)||8 (63%)||16 (70%)||0.431c|
|2 siblings||4 (36%)||2 (15%)||6 (26%)||0.562c|
|3 siblings||2 (18%)||0 (0%)||1 (4%)||0.203c|
|Meeting criteria ADHD/ODD|
|ADHD||11d (100%)||13d (100%)||0d (0%)|| |
|ODD||6 (55%)||5 (38%)||1 (4%)||0.001|
Baseline comparison of FRI and FSI in ADHD and no-ADHD control families
At baseline, the FRI and the FSI scores of the ADHD group preceding randomization (n = 24) were similar to the scores of the no-ADHD control group (n = 23; see Table 2). Also no differences were found between the ADHD RED group (n = 11) and the ADHD control group (n = 13). Both ADHD groups showed significantly more conflicts on the conflict subscale than the no-ADHD control group, whereas on the other subscales no significant differences were found. When compared to the norm scores provided by the FES-manual, significantly higher scores of FRI and FSI were found in both ADHD groups and in the no-ADHD control group at baseline.
Table 2. FES ratings in ADHD group, no-ADHD control group and the FES-manual norm, prior to randomization
| ||1 n = 24||2 n = 23||3 n = 941||Difference 1–2a||Difference 1–3b||Difference 2–3b|
|ADHD group||No-ADHD Control group Mean (SD)||Norm||Mean difference||p-value||Cohen's d||Mean difference||p-value||Cohen's d||Mean difference||p-value||Cohen's d|
|Cohesion||8.9 (1.7)||9.1 (0.9)||8.5 (2.0)||−0.2 (−1.0–0.4)||0.59||−0.2||0.4||0.134||0.2||0.6||0.003||0.4|
|Expressiveness||10.1 (1.3)||9.7 (1.2)||8.3 (2.2)||0.3 (−0.4–1.1)||0.352||0.3||1.8||<0.0001||1.0||1.4||<0.0001||0.8|
|Conflict||4.7 (2.2)||3.0 (2.1)||5.0 (2.5)||1.7 (0.5–2.9)||0.007||0.8||−0.3||0.256||−0.1||−2.0||<0.0001||−0.9|
|Organization||8.3 (1.5)||8.7 (1.0)||8.0 (2.3)||−0.4 (−1.2–0.3)||0.230||−0.3||0.3||0.175||0.2||0.7||0.002||0.4|
|Control||9.5 (1.3)||9.5 (1.2)||8.5 (2.1)||0.0 (−0.7−0.7)||0.951||0.0||1.0||0.001||0.6||1.0||<0.0001||0.6|
|FRI||25.3 (3.8)||26.8 (2.9)||22.9 (3.4)||−1.5 (−3.5–0.4)||0.123||−0.4||2.4||0.003||0.7||3.9||<0.0001||1.2|
|FSI||17.8 (2.1)||18.3 (1.7)||16.5 (3.8)||−0.5 (−1.6–0.7)||0.429||−0.3||1.3||0.003||0.4||1.8||<0.0001||0.6|
Effects of RED on FRI and FSI
The FRI and FSI baseline and endpoint scores of the ADHD RED group and ADHD control group are presented in Table 3. No intervention effect was found on the FRI and FSI, neither in the ADHD RED group nor in the ADHD control group. Furthermore, no intervention effect was found on the two FES subscales not linked to the two indices, that is, family values and social orientation.
Table 3. Comparison of ADHD score, ODD score and FES ratings within and between ADHD RED group and ADHD control group at start and at end of trial
| ||ADHD RED N = 11||ADHD Control N = 12||End rating ADHD Control versus ADHD RED group, adjusted for score at start|
| ||Start||End|| || || ||Start||End|| || || || || |
| ||Mean (SD)||Mean difference (95% CI) start-end||p-value||Cohen's d||Mean (SD)||Mean difference (95% CI)||p-value||Cohen's d||Mean difference (95% CI)||p-value|
|ADHDa||44.6 (4.1)||18.1 (12.9)||26.5 (18.2–34.9)||<0.0001||2.8||46.0 (4.2)||43.7 (7.1)||2.3 (−0.–5.6)||0.156||0.4||25.1 (16.4–33.8)||<.0001|
|ODDa||3.3 (2.0)||2.0 (2.0)||1.3 (−0.2–2.8)||0.101||0.7||3.2 (2.3)||2.9 (2.6)||0.2 (−0.3–0.8)||0.411||0.1||1.0 (−0.5–2.5)||.201|
|Cohesion||8.7 (1.4)||8.9 (1.1)||−0.2 (−0.9–0.5)||0.606||−0.2||8.9 (2.0)||9.0 (1.6)||−0.2 (–0.7.–0.4)||0.575||−0.1||−0.1 (−0.8–0.7)||.883|
|Expressiveness||10.1 (1.2)||10.0 (1.6)||0.1 (−0.2–0.4)||0.576||0.1||10.2 (1.5)||10.0 (1.1)||0.2 (−0.4–0.7)||0.538||0.2||0.1 (−0.6–0.7)||.840|
|Conflict||5.6 (2.2)||4.7 (2.2)||0.8 (0.0–1.6)||0.041||0.4||4.3 (1.6)||3.8 (1.5)||0.5 (−0.1–1.1)||0.083||0.3||−0.1 (−1.0–0.9)||.904|
|Organization||8.4 (1.4)||8.6 (0.7)||−0.2 (−0.8–0.5)||0.606||−0.2||8.1 (1.6)||8.0 (1.6)||0.1 (−0.6–0.7)||0.804||0.1||0.4 (−0.4–1.2)||.332|
|Control||9.4 (1.0)||9.8 (1.0)||−0.5 (−0.8–0.1)||0.004||−0.4||9.5 (1.4)||9.6 (1.5)||−0.1 (−0.6–0.5)||0.772||−0.1||0.3 (−0.3–1.0)||.295|
|FRI||24.3 (3.2)||25.2 (3.2)||−0.9 (−2.1–0.3)||0.136||−0.3||25.8 (4.0)||26.3 (2.8)||−0.5 (−1.8–0.8)||0.455||−0.1||−0.1 (−1.6–1.4)||.882|
|FSI||17.7 (1.7)||18.4 (1.0)||−0.6 (−1.4–0.2)||0.121||−0.5||17.6 (2.7)||17.6 (2.8)||0.0 (−1.1–1.1)||1.000||0.0||0.7 (−0.6–1.9)||.282|
Effects of RED on ADHD and ODD symptoms taking into account any effects of family relationships and family structure
The effects of the diet intervention on ADHD and ODD are shown in Table 3. The analysis of the ADHD score using a repeated measurement design showed that FRI was significantly associated with the ADHD score, independent of ADHD group and measurement moment (estimate −0.8, 95% CI = −1.5–−0.1, p = .024, see Figure 2). Consequently, there seems to be an inverse relationship between the number of ADHD sympoms and the family relationship: the higher the ADHD symptom score, the less the FES Relationships Index score. The two-way and three-way interactions with group and measurement point were nonsignificant. No effect of FSI on ADHD score was found (estimate 0.8, 95% CI = −0.2−1.8, p = .134), and the two-way and three-way interactions were non-significant, suggesting that changes in both FRI and FSI did neither mediate nor moderate the results of the RED on ADHD symptoms.
Figure 2. Family relationship index (a), family structure index (FSI) (b) and Predicted attention-deficit hyperactivity disorder (ADHD) total score for ADHD control and ADHD restricted elimination diet (RED) group at start and end. Prediction based on the final GEE model. Family relationship index (FRI) (a), family structure index (b) and predicted oppositional defiant disorder (ODD) total score for ADHD control and ADHD RED group at start and end. Prediction based on the final GEE model. The dots in the figures (▲●) represent the predicted values of the ADHD (ODD) scores based on the statistical model, and thus also dependent on the FRI (FSI) scores. The lines in the figures represent regression lines of the predicted ADHD (ODD) scores in relation to the FRI (FSI) scores. An increasing line indicates that the ADHD (ODD) score increases with FRI (FSI) score, a decreasing line indicates the opposite
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A similar analysis for ODD score equally showed a significant association for FRI, independent of ADHD group and measurement moment (estimate −0.2, 95% CI = −0.4–−0.03, p = .022), indicating that a higher FRI was related to less ODD symptoms (see Figure 2). No effect of FSI on ODD score was found (estimate 0.2, 95% CI = −0.1–0.5, p = .238). Again two-way and three-way interactions were non-significant, suggesting that changes in both FRI and FSI did neither mediate nor moderate the results of the RED on ODD symptoms.
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The main aim of this pilot study was to investigate whether the beneficial behavioural effects in children with ADHD following an RED (Pelsser et al., 2011), may be explained by an improvement of family environment, that is, family relationships and family structure. Our findings indicate that (1) family environment in families of children with ADHD, motivated to follow a 5-week RED, is similar to the family environment of a no-ADHD control group and better than the FES-manual norm; (2) family relationships and structure are not affected by following a 5-week RED; (3) the effects of an RED on ADHD and ODD symptoms are not mediated by changes in family relationships and structure (in fact, there were no changes in FRI and FSI); (4) family relationships but not family structure are inversely associated with ADHD and ODD.
At baseline we did not find any significant differences in family environment between the ADHD group (n = 24) and the no-ADHD control group (n = 23), nor between the ADHD RED group (n = 11) and the ADHD control group (n = 13). All groups, however, showed a better family environment compared to the norms. Consequently, relationships and structure of ADHD families taking part in this study were (more than) adequate. These findings are consistent with the findings of Pimentel, Vieira-Santos, Santos and Vale (2011), who found that parental practices of mothers of children with ADHD were similar to those of a validation sample. Conversely, our results are contrary to the findings of Kepley and Ostrander (2007) who found that families with ADHD were less cohesive and expressive than families without ADHD. This discrepancy may be caused by the fact that, in advance, parents were adequately informed about the stringency of the diet. It is further conceivable that parents who dreaded this challenge would decide not to participate, and that only parents who were confident of their parenting capacities, would decide to participate. Consequently, our sample may have consisted of families with an above-average family environment only.
We found no differences in family relationships and structure when comparing the start and end measurements of both ADHD groups. Consequently, in our sample the RED did not affect family environment; the restricted diet instigated neither any favourable nor any deleterious effects on the parent–child relationship. Unfortunately, considering that all families in the ADHD RED group completed the study, we could not investigate the parenting capacities of parents not complying with the diet.
The results of the RED on the behavioural outcomes of the ADHD group, that is, statistically significant and clinically relevant improvements of ADHD and ODD in 64% of the children, have been discussed elsewhere (Pelsser et al., 2011). Considering the analyses of two-way and three-way interactions of the family relationships and structure indices and behaviour, with group and measurement point as independent variables, we did not find evidence that family relationships and structure mediate the effect of the RED on ADHD and ODD symptoms. However, we found an inverse association between family relationship and both ADHD and ODD symptoms, that is, a higher FRI score co-occurred with less ADHD and ODD symptoms. These findings are consistent with the findings of Deault (2010), showing that ADHD is associated with conflicted parent–child relationships. We found no significant association between family structure and both ADHD and ODD symptoms.
Limitations of this study should be noted. First, the ADHD group only consisted of families with a good family environment. It is conceivable that families with less adequate family environments were deterred from following an RED, which may have led to a sample bias. We would like to argue that all clinical trials asking specific commitment and efforts may inevitably lead to a highly motivated sample of subjects entering the trial, thus resulting in a study population not reflecting the real-life heterogeneity of subjects. Consequently, our study results are applicable only to those families with both a good family environment and sufficient motivation to undertake a 5-week diet. Concurrently, our study may indicate that in families meeting the conditions of both a good family environment and a positive attitude towards a 5-week diet an RED is a feasible intervention in children with ADHD. Second, it is conceivable that parenting problems might impede the compliance to and the completion of the RED, but this aspect could not be investigated because all families assigned to the ADHD RED group completed the diet. Third, although promising, the sample size in this study is small, and replication in a larger group of children is advised. Still, we would like to argue that our study results confirm the findings of two double-blind placebo-controlled diet studies using a restricted verum diet (diet group) and a restricted sham diet (control group) [Kaplan, McNicol, Conte & Moghadam,1989; Schmidt et al., 1997]. Both studies resulted in behavioural improvements in the diet group only (abbreviated Conners' Scale effect sizes 0.55 and 0.59 respectively), thus indirectly showing that the children's behavioural changes were not due to changes in parenting capacities.
Concluding, the results of our pilot study suggest that, in families with good family environment and motivated to follow an RED, the behavioural improvements of children with ADHD and ODD following an RED are not mediated by improvements of family relationships and structure. Replication of this study, in larger groups of children, is advised.
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This study was supported by grants from the Foundation of Child and Behaviour.
LMP is franchiser of the ADHD Research Centre. In the past 3 years, JKB has been a consultant, member of advisory board, speaker, or a combination thereof for Janssen Cilag, Eli Lilly, Bristol-Myers Squibb, Schering Plough, UCB, Shire, Medice and Servier.
All other authors declare that they have no conflicts of interest.
We thank all parents, children and teachers who participated in this study.