In a recent study published in eClinicalMedicine, researchers investigated whether walnut consumption can improve adolescents' neuropsychological and behavioral development.
Study: Effect of walnut consumption on neuropsychological development in healthy adolescents: a multi-school randomized controlled trial. Image Credit: CalypsoArt/Shutterstock.com
Background
Omega-3 polyunsaturated fatty acid molecules are essential for the neuropsychological development of individuals.
The teenage brain, especially the prefrontal cortex, a mediator of cognition, executive functions, working memory, and logical thinking, is sensitive to several lifestyle and environmental factors, including exposure to particular nutrients and food items.
Walnuts are rich dietary sources of omega-3 alpha-linolenic acid (ALA), the precursor fatty acid for longer-chain eicosapentaenoic (EPA) acid docosahexaenoic (DHA) acid.
However, the potential benefits of eating walnuts, a rich source of plant-derived omega-3 alpha-linolenic acid (ALA), on adolescent neurodevelopment are not well-characterized and require further investigation.
About the study
In the present randomized controlled trial, researchers explored the potential neuropsychological and socio-emotional behavioral benefits of consuming walnuts.
The WALNUTs Smart-Snack (WSS) trial was conducted between 1 April 2016 and 30 June 2017 across 12 high-level schools located in Spain.
In total, 771 healthy 11 to 16-year-olds were randomly allocated in a 1:1 ratio to receive 30.0 grams daily of raw Californian walnut kernels for dietary consumption over six months, to meet recommended dietary allowance was 2.50 grams of omega-3 fatty acids daily or no walnuts (controls).
Each walnut was estimated to contain 9.0 grams of ALA per 100.0 grams of a walnut). The primary study outcomes related to neuropsychological (attention, working memory, executive functions, and fluid intelligence) and behavioral (attention deficit hyperactivity disorder (ADHD) symptomatology and socio-emotional endpoints) development were evaluated.
Erythrocyte ALA levels were measured before and after the intervention among 170 walnut-consuming individuals and 163 control individuals to assess adherence to the intervention objectively.
Before randomization, data on participants' sex, maternal educational attainment, and age were obtained using brief telephonic questionnaires.
All individuals completed food frequency questionnaires (FFQ). Adherence to the Mediterranean diet was assessed using the KIDMED Index. The Attention Network Test (ANT) was used to assess attention, and the N-back task was used to assess working memory.
The Roulettes Task was used to assess risky decision-making (executive function), and the inductive reasoning subtest of the Tests of Primary Mental Abilities (PMA-R) was used to assess fluid intelligence.
Problem behavior was assessed using the self-reported version of the Strengths and Difficulties Questionnaire (SDQ). Linear mixed-effects-type modeling was performed for the intention-to-treat (ITT) analyses.
In addition, the per-protocol (PP, adherence-adjusted) effect of consuming walnuts for six months was analyzed by the inverse-probability weighting method, accounting for the post-randomization prognosis-affecting factors (inclusive of adherence) based on generalized estimating equations (GEE).
Individuals aged >16.0 years, regularly consuming omega-3 fatty acid supplements and/or walnuts, and individuals with self-documented walnut or gluten allergies were excluded from the analysis.
The team also excluded lactose-intolerant individuals and those documenting dry fruits, cereals, soy, peanuts, sulphites, and sesame allergies. In addition, the PubMed database was searched on 1 June 2022 for relevant records, including animal studies and clinical trials.
Results
The mean age of the participants was 14 years. In the ITT analyses, no significant differences were observed between the groups at six months for the primary study endpoints.
Erythrocyte ALA percentage increased significantly among walnut-consuming individuals. Adolescents consumed walnuts for 70.0 (mean) days, and 34% (n=133) of individuals adhered to >50% of the intervention period.
The success rate of retesting at six months was 84%. The PP effect on attention score improvement was −11.0 ms among walnut consumers compared to controls.
The enhancement in scores for fluid intelligence and the decrease in ADHD symptom scores were 1.8 and −2.2, respectively.
Erythrocyte alpha-linolenic acid levels rose by 0.030% and 0.010% in the intervention and control groups, respectively. Sensitivity analyses performed with data adjustments for baseline values yielded similar results.
The literature search yielded one observational-type study, comprising children and adolescents, and a small intervention study comprising young adults, determining the association between nut intake and cognition in a sample population similar to that of the present study.
Both studies reported positive associations between consuming walnuts and cognitive functioning.
Conclusion
Overall, the study findings showed that consuming walnuts for six months showed no significant improvements in the neuropsychological functioning of healthy teenagers.
However, enhancements in fluid intelligence, ADHD symptomatology, and attention were noted among adolescents showing better compliance with the study intervention.
Further research must be conducted, including magnetic resonance imaging (MRI) and functional MRI (fMRI) of the brain, longer intervention periods, and the mechanisms underlying the neuropsychological benefits of walnut consumption must be elucidated.
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