Young adults who ate a handful of walnuts with breakfast saw a long-lasting improvement in their reaction times and a boost in memory performance hours later, according to a new study. The findings strengthen the claim that walnuts are a brain-enhancing food.
According to the Doctrine of Signatures, which has been around since pre-scientific times, the physical characteristics – or ‘signature’ – of certain plants were indicative of their therapeutic value. A carrot cut crosswise resembles an eye, so it was said to improve vision. The thing is that subsequent scientific discoveries, such as carrots containing vision-maintaining beta-carotene, would often validate the Doctrine’s claims.
A new study led by researchers at the University of Reading in the UK has confirmed another of the Doctrine of Signatures’ claims. They found that eating a breakfast rich in walnuts – those miniature brain doppelgängers – had a positive effect on brain performance that lasted throughout the day.
“This study helps strengthen the case for walnuts as brain food,” said Claire Williams, a professor of neuroscience at the University and the study’s corresponding author. “A handful of walnuts with breakfast would give young adults a mental edge when they need to perform at the top of their game. It’s particularly exciting that such a simple dietary addition could make a measurable difference to cognitive performance.”
The researchers recruited 32 healthy adults aged 18 to 30 and randomly assigned them to a treatment or control group. The treatment group ate one meal of muesli and vanilla yoghurt mixed with 50 g – around 1.5 ounces, a generous handful – of crushed walnuts for breakfast. The control group’s breakfast consisted of yoghurt and muesli without nuts. Forty grams of melted butter was added to the control group’s meal so that the two interventions were well-matched in macronutrients, total weight, and total number of calories. After one week, the participants returned and consumed the meal they hadn’t eaten the first time. Blood tests and cognitive and EEG measurements were taken at baseline and then at either two, four, or six hours after breakfast.
After a single walnut-rich breakfast, participants showed faster reaction times during cognitive tasks measuring executive function, the set of mental skills that are used to manage everyday tasks like making plans, problem-solving and adapting to new situations. The effect lasted throughout the day. The effects of the walnuts on memory were mixed. Compared to the control group, the walnut group showed worse memory performance at two hours, but by six hours, they outperformed the control. The researchers think this may have been due to the slower absorption of the nut’s beneficial omega-3s and proteins.
EEG recordings revealed differences in brain activity in the walnut group compared to the control group during memory recall and executive function testing. The differences were seen in the frontoparietal region, an area associated with episodic memory, attention, and executive functions such as switching tasks. Interestingly, the researchers found that the effect of walnuts on mood was “unexpectedly negative” and not in keeping with previous research. They said one possible explanation for the participants’ low mood, especially immediately after eating, was the walnut meal’s taste, smell, and palatability, which they’d rated worse than the control.
This is the first study to examine the immediate effects of walnuts on brain function in young adults and more research is needed to understand better how walnuts produce these beneficial brain effects.
The researchers note that the study was funded by the California Walnut Commission but that the Commission did not contribute to the design or implementation of the study nor the interpretation of its findings.
The study was published in the journal Food & Function.
Source: University of Reading
