Can eating walnuts improve children’s cognitive development? Original paper

In this randomized controlled trial, walnut consumption improved attention, fluid intelligence, and ADHD symptoms in children with high adherence to the intervention.

The effect of walnut consumption on behavioral and neuropsychological development.

771 children and adolescents (ages 11–16; 54% girls, 46% boys) without apparent health conditions.

The researchers conducted a randomized controlled trial at multiple schools for a duration of 6 months. The intervention group received 30 grams of raw walnuts daily to incorporate into their regular diet, and the control group received no intervention.

The primary endpoints for assessing neuropsychological development included attention, working memory, fluid intelligence, and executive function. Behavioral development was evaluated based on attention deficit hyperactivity disorder (ADHD) symptoms.

To measure adherence in the intervention group, the researchers analyzed the blood levels of alpha-linolenic acid (ALA), an omega-3 fatty acid derived from walnuts that has potential benefits for brain function.^[1]

At the end of the study, the researchers examined the results using two different approaches: intention-to-treat analysis, which considered all participants' outcomes regardless of their walnut consumption, and per-protocol analysis, which focused solely on participants who followed the prescribed walnut intervention, excluding those who did not.

In the intention-to-treat analysis, walnut consumption had no statistically significant effects on behavioral and neuropsychological development compared to the control. Blood levels of ALA were slightly higher in the walnut group compared to the control group, indicating moderate adherence to the intervention.

In the per-protocol analysis, which only considered the participants who adhered most to the intervention, walnut consumption improved certain aspects of behavioral and neuropsychological development. These improvements included a reduction in ADHD symptoms and an increase in attention and fluid intelligence. The ALA levels in the per-protocol intervention group also increased, indicating better adherence compared to the intention-to-treat group.

This study emphasized two important points in nutrition research: the significance of adherence, which can be challenging to achieve, and the impact of statistical analyses on the study outcomes.

Although the intention-to-treat analysis did not reveal apparent benefits of walnut consumption, it holds more weight than the per-protocol analysis because it reflects real-world conditions and preserves the benefits of randomization. However, the intention-to-treat analysis may underestimate the treatment effect if there is a substantial amount of nonadherence to the intervention or dropout. Hence, additional analyses like the per-protocol analysis are often conducted to better understand the treatment's efficacy under optimal conditions.

Because both approaches have their own strengths and weaknesses, researchers commonly present the results of both analyses to offer a comprehensive understanding of the study outcomes. Nevertheless, this can pose challenges for lay people when attempting to interpret the results.

So, what do these results imply? In general, the findings of this study demonstrate that daily walnut provision can have a beneficial impact on the behavioral and neuropsychological development of adolescents. However, it is crucial to recognize that the decision of whether or not children choose to consume walnuts can have a significant impact on whether these beneficial effects are realized.

Two of the trial investigators have received funding from the California Walnut Commission and one of the investigators has received grant funding from the International Nut and Dried Fruit Council. The California Walnut Commission also supplied the walnuts used in the trial.