Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder marked by persistent patterns of inattention, hyperactivity, and impulsivity that interfere with daily functioning. Nutrition is becoming increasingly important in the treatment of ADHD, and dietary interventions are being researched as a supplement to medication or as a substitute. This article explores the potential of dietary interventions, particularly focusing on the oligoantigenic diet (OD) and its impact on ADHD symptoms, including impulsivity.
Understanding ADHD and Its Complexity
ADHD has undergone sustained development and continuous refinement of its definition and understanding over the last five decades. The worldwide prevalence varies greatly between 5 and 10% for children and 4% for adults, depending on geographical, cultural, and diagnostic factors. Despite the multitude of findings, the appropriate treatment of ADHD remains a very complex issue. Impulsivity, in this context, refers to rapid, unplanned reactions to stimuli with limited regard for consequences, such as interrupting others or difficulty delaying responses.
Pharmacotherapy, especially psychostimulants, is the most common treatment, with a response rate of around 70% in children aged five or older. However, pharmacological therapy can cause negative side effects and long-term consequences, such as gastrointestinal diseases and sleep disturbances. These effects vary between patients due to psychological aspects, genetics, and neurological structures. As a result, non-pharmacological approaches are increasingly being researched and used, either as a supplement to medication or as a substitute.
The Role of Nutrition in ADHD
External factors can increase or decrease ADHD symptoms, resulting in further potential treatment methods. The significant influence of food intolerances on behavioral disorders was introduced 100 years ago, supported by the hypothesis that avoiding certain foods (such as milk and chocolate) as part of a diet could reduce the corresponding symptoms. Numerous findings have demonstrated the significant influence of nutrition, particularly regarding ADHD symptoms. For example, children with ADHD show a significantly higher prevalence of lactose intolerance. Studies have also shown an association between ADHD symptoms and celiac disease, with a gluten-free diet leading to a significant reduction in the corresponding symptoms. These results emphasize the potential of non-drug methods in the treatment of ADHD.
A promising approach is the oligoantigenic diet (OD), which avoids foods associated with intolerances or allergies. In a corresponding study, the participants ate hypoallergenic foods following previous studies on migraine in children. Apart from vitamin supplementation and calcium-rich water, the diet contained vegetables, two fruits, two sources of carbohydrates, and two types of meat. A total of 82% of all participants showed a significant reduction in ADHD symptoms, and 29% showed normal behavior at the end of this study. Several recent studies have demonstrated this significant impact of the OD.
Read also: Shopping List for ADHD Diet
The Oligoantigenic Diet (OD) and Its Effects
The oligoantigenic diet (OD) involves avoiding certain foods that often trigger intolerances and allergies. Previous studies have shown that around 60% of patients experienced a significant reduction in ADHD symptoms after completing such a diet. One study aimed to further confirm the efficacy of the OD within an analysis focusing on the symptom of impulsivity.
Study Methodology
In the study, the Parent Rating of the Diagnostic System of Mental Disorders in Children and Adolescents (DISYPS-II FBB-ADHD) questionnaire was used to measure the severity of ADHD symptoms. Of 34 children and adolescents (between 7 and 18 years of age) screened and included in this study, 31 participants completed the 4-week OD diet.
Key Findings
The post-diet analysis showed significant short-term improvements for the DISYPS-II FBB-ADHD total score, compared to the start of the diet. This pattern of results also applied to the respective subscales of the DISYPS-II FBB-ADHD questionnaire. A follow-up evaluation conducted 3.5 years after the intervention with 21 participants suggested that the improvements in ADHD symptoms were maintained over time. Specifically, 66.7% of the participants continued to meet the responder criterion, with particularly notable and lasting reductions in impulsivity.
Discussion
These results suggest that the beneficial effects of the oligoantigenic diet followed by identifying and avoiding individual intolerant foods may persist long term, and participants’ dietary habits may have also evolved over the years.
Materials and Methods: A Deeper Dive
The Ethics Committee of the University approved this study in accordance with the World Medical Association’s Declaration of Helsinki.
Read also: Strategies for Weight Loss with ADHD
Participants
Recruitment took place at the inpatient and outpatient units of the Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics of the Medical Center. This study included children and adolescents aged 7 to 18 who were attending at least the 2nd grade of a general education school and had a confirmed ADHD diagnosis according to both the DSM-IV and ICD-10 criteria. Participation required agreement with the study procedure and informed consent from both the participants and their parents. The exclusion criteria included severe concomitant diseases or neurological or organic comorbidities not amenable to dietary interventions, lack of compliance from parents and/or children, insufficient reading or writing skills of legal guardians and/or children, concurrent drug therapy for ADHD, participation in other studies, or adherence to a special diet (e.g., vegetarian, vegan).
A total of 34 children took part in this study between 2014 and 2023. After the completion of the OD, 31 participants with a mean age of M = 10.50 (SD = 2.28) years were included in this study. In the follow-up analysis, data from 21 participants were available, with a mean age of M = 14.10 (SD = 2.09) years.
Procedure
The study comprised several phases, including a pre-diet phase, a diet phase, a reintroduction phase, and a follow-up.
Pre-Diet Phase
Participants were enrolled between 2014 and 2017, with additional recruits in 2021. At the baseline assessment, the ADHD diagnoses were confirmed using the Kiddie-SADS-PL interview. Comprehensive medical histories, including symptoms and allergies, were collected, followed by psychiatric and medical examinations. Following the baseline assessment, a two-week pre-diet phase commenced. During this period, participants maintained their usual dietary habits, and parents precisely recorded all food and beverage intake in detailed food diaries. This phase also served to prepare participants for the subsequent diet phase.
Diet Phase
During the four-week diet phase, participants adhered to a restricted diet of oligoantigenic foods with low allergenic potential, according to the protocols of Egger and Pelsser et al. Excluded from the diet were pig and cow meat, wheat, soy, and corn products, while lamb, turkey, potatoes, rice, and various vegetables were permitted. Parents received comprehensive dietary instructions, including lists of acceptable foods, grocery lists, and recipes. Family members were encouraged to follow the diet to support adherence. Participants attending full-time school were required to consume home-prepared meals. A nutritionist supervised the diet to ensure it met all essential nutritional requirements and provided guidance on supplementation when necessary.
Read also: Managing ADHD Symptoms with Food
Reintroduction Phase
Participants whose ARS value decreased by more than 40% between T1 and T2 were classified as responders, according to Pelsser et al. Non-responders could finish this study and receive the usual treatment. Responders began the reintroduction phase to gradually return to their usual diet, testing new foods every three to four days in this order: milk products, favorite foods, eggs, grain products, fish, meat, vegetables, fruits, and nuts. If behavioral changes or symptoms such as abdominal pain, headaches, or allergic reactions occurred, the psychiatrist and dietitian were notified, and the triggering food was avoided. Reactions could occur from ten minutes to several days after ingestion. Only the tolerated foods were consumed for three days after each test. Approximately six weeks after the beginning of the reintroduction phase, a control appointment was conducted. After testing all common nutrients, the final study appointment took place, where personalized dietary recommendations were provided. Children were advised to avoid problematic foods for one year, after which these foods could be retested.
Follow-Up
The follow-up examination occurred 2.50 to 5.37 years after the diet started (M = 3.33 years, SD = 1.15). Both responders and non-responders were re-interviewed to evaluate their benefits from the diet. During this period, adherence to the original oligoantigenic diet was required for responders, and the individual intolerant foods should be avoided. Short-term dietary interruptions occurred, which can be assumed as not causing effects on long-term follow-ups; the non-responders reported an eating pattern as usual. Accordingly, the long-term outcomes were assessed using standardized interviews. This approach allowed us to capture the sustainability of the initial treatment effects while accommodating individual modifications in “dietary behavior over time”.
Outcome Measures
The primary outcome was assessed using the ADHD Rating Scale IV (ARS), consisting of 18 items divided equally between the inattention and hyperactivity/impulsivity subscales. Each question is rated as “Never or rarely” (0), “Sometimes” (1), “Often” (2), or “Very often” (3). The ARS was conducted at each appointment by the study clinician, who interviewed the parents in the presence of the child. A symptom improvement of more than 40% between the two appointments, T1 (before the diet) and T2 (after the diet), was defined as a response.
Three questionnaires were used as secondary outcome measures: the Child Behavior Checklist 4-18 (CBCL/4-18), the Inventory of Life Quality in Children and Adolescents (ILC), and the DISYPS-II FBB-ADHD. For this study, the DISYPS-II FBB-ADHD was used for a more detailed assessment of ADHD symptoms. The assessment form is suitable both for confirming the diagnosis and for monitoring the progress of the ADHD symptoms. The DISYPS-II FBB-ADHD questionnaire consists of 35 items designed for diagnostic confirmation and symptom monitoring. The instrument comprises a total scale and three subscales: inattention, hyperactivity, and impulsivity, with hyperactivity and impulsivity treated as separate subscales. Each item is rated on a four-point rating scale from 0 (not at all) to 3 (very much).
Regarding the reliability and validity of the DISYPS-II FBB-ADHD, a study highlighted its distinctive three-factor structure (Inattention, Hyperactivity, Impulsivity), which reflects the core symptoms of ADHD. It is the only ADHD-specific rating scale to also assess competencies, potentially making it more sensitive to therapy-related changes. The reliability of the subscales and overall ADHD score ranged from satisfactory to very good, aligning with international reliability values.
Statistical Analysis
Analysis of DISYPS-II FBB-ADHD consisted of two different parts depending on different time points. Firstly, the immediate effect of the OD was analyzed by comparing the DISYPS-II FBB-ADHD scores at the pre-diet phase and the post-diet phase.
The Broader Dietary Landscape and ADHD
Research extends beyond oligoantigenic diets to explore broader dietary patterns and their effects on ADHD.
Dietary Patterns and ADHD Symptoms
One study conducted in China examined the relationship between dietary patterns and ADHD symptoms in preschoolers. The study identified five dietary patterns, with the "processed" dietary component explaining the highest percentage of variability. After controlling for potential confounders, preschoolers in the top quintile of the "processed" and "snack" dietary pattern scores had greater odds of having ADHD symptoms compared with those in the lowest quintile. This study suggests that preschoolers tend to choose unhealthy dietary patterns, which may be associated with increased ADHD symptoms.
Global Nutrient Supply and ADHD
Another study investigated the association between nutrient supply, socioeconomic status, and ADHD disease burden at a global level over time. The study collated ADHD disease burden, macronutrient supply, and gross domestic product (GDP) from more than 150 countries from 1990 to 2018 and analyzed them with nutritional geometry generalized additive mixed models (GAMMs). The modeling results suggested the interactive effects of nutrients and socioeconomic status on ADHD. Fat, especially plant-based fat supply, is associated with decreased ADHD disease burden. These associations were conserved across sexes and ages and were not confounded by the total energy supply. This study suggests that plant-based fat supply seemed to drive the reduction of ADHD disease burden, which is supported by previous reports about the amelioration of ADHD by ketogenic diets.
Plant-Based Diets and ADHD Risk
Attention-deficit hyperactivity disorder (ADHD) is the most prevalent neurodevelopmental disorder with a prevalence of 5% among children and adolescents worldwide. Plant foods have a protective effect against inflammation and oxidative stress which both are involved in psychiatric disorders pathophysiology including ADHD. A case-control study was conducted on 345 children and adolescents 7-13 years old in Yazd, Iran. Subjects were categorized into the case (n = 113) and control groups (n = 232) based on matching age and sex. To diagnose ADHD, the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSMIV-TR) was used. Food frequency questionnaire was used to measure food intake. Children in the highest quartile of PDI compared to the lowest quartile had a higher energy and macronutrient intake, calcium, zinc, iron, vitamin B12, B6, and folic acid. After adjusting for potential confounders, a significant decreasing trend in the odds of ADHD across increasing quartiles of the PDI (P-trend = 0.001) was observed. In addition, children in the fourth quartile of PDI had 68% lower odds of ADHD than the first quartile. This study found that PDI is associated with lower risk of ADHD in children.
Dietary Interventions: The Few-Foods Diet (FFD)
Dietary interventions can modulate behavior and mental health. Supplementation or restriction of some nutrients or foods have generally shown small effects in relieving ADHD symptoms. However, meta-analyses of double-blind placebo-controlled (DBPC) diet restriction studies have reported moderate to large effect sizes when applying a modified few-foods diet (FFD). Based on the evidence provided by the DBPC studies, the FFD was included in an ADHD treatment protocol. Subsequent open or single-blinded randomized controlled trials did apply an optimal FFD showing large effects, while a recent uncontrolled FFD study in children with ADHD showed significant behavioral improvements according to blinded video ratings as well as to non-blinded assessments.
FFD and Brain Activation
Knowledge about the mechanism underlying the effect of an FFD on ADHD may provide a better understanding of the association between diet and ADHD. Since ADHD has been associated with impaired cognitive control processes in the brain, such as response inhibition and interference inhibition, one study aimed to investigate whether behavioral changes after following an FFD are associated with changes in brain activation during inhibition tasks in children with ADHD. Children with ADHD have decreased activation in various brain regions during inhibition, including the prefrontal cortex, putamen, thalamus, precuneus and parietal and temporal lobes.
The study's primary objective was to investigate whether ADHD symptom changes following an FFD are reflected in neural activation changes in the brain. To assess brain activation, fMRI measurements of BOLD responses during response inhibition (stop-signal task) and interference inhibition (Flanker task) were compared before (t1) and after (t2) a 5-week FFD intervention. The study hypothesized that the observed changes in ADHD symptoms after the intervention are associated with changes in activation of brain regions that are involved in task execution, using task-related regions-of-interest (ROIs).
Study Results: FFD and Brain Activation
Between February 19, 2018, and April 30, 2019, 138 children were screened for participation in the BRAIN study. Of the 100 children that started with the FFD, 12 stopped the diet prematurely and nine were excluded from analysis. Of the remaining 79 children, 53 were included for the stop-signal task and 32 for the Flanker task analyses. Sixty-eight of 79 children followed the most restricted FFD; 11 children were kept on the extended FFD, because their parents reported major behavioral improvements of 72-98% while following the extended FFD.
ADHD symptom scores were measured using the ADHD Rating Scale (ARS). At the end of the FFD (t2), the mean ARS score was significantly lower than the mean ARS score at t1. Fifty (63%) of 79 participants showed an ARS score decrease of at least 40% and were categorized as responders, with an average decrease of 73.4%, while non-responders showed an average decrease of 10.8%.
The task performance results of the stop-signal task showed that both the average reaction time (RT) for the frequent Go trials (GoRT) and the average time it took to inhibit a response for the infrequent stop-signal trials (stop-signal reaction time [SSRT]) across participants did not differ between t1 and t2. The Flanker task performance results showed a congruency effect, i.e., participants were slower and made more errors on incongruent than on congruent trials at both t1 and t2.
Functional ROIs representing the main task effect across timepoints and participants were determined, independent of the ARS response. The main task contrasts during the stop-signal task activated brain regions in frontal, parietal, temporal and occipital lobes as well as cerebellar and sub-cortical regions involved in response inhibition.
Whole-brain fMRI analyses of the t2-t1 effects during the stop-signal task did not reveal differences in brain activation. However, when taking the changes in ARS score into account, both response inhibition contrasts showed a positive correlation between change in ARS score and change in precuneus activation, at the whole-brain, cluster-level corrected threshold pFWE < 0.05.
Impact on Oppositional Defiant Disorder (ODD) Symptoms
ODD was present in 58 of 79 children at t1. For these 57 children, the mean ODD score at t1 was 17.8. At t2, the mean ODD score was reduced to 7.6. Forty (69%) of 57 participants showed a decrease in ODD symptoms of more than 40%, with an average symptom decrease of 75.4%. Changes in ODD score and ARS score are strongly correlated.
Dietary Guidance and Resources
For individuals seeking to implement dietary changes for ADHD management, resources are available to provide guidance and support. Plant-based foods offer protective effects related to their antioxidant and anti-inflammatory properties. These foods are also rich in micronutrients. Probiotics and high-fiber foods are also beneficial. Food sources of probiotics include tempeh, non-dairy yogurts with live cultures, fresh sauerkraut and fresh pickles with live active cultures. Organisms in probiotics feed off of fiber in plant foods, especially foods high in soluble fiber like legumes (beans, lentils, soy), flaxmeal, chia seeds, oats, barley and skins of fruits like apples and grapes.