In the California Walnut Commission-sponsored study, researchers from Michigan’s Andrews University gave two groups of students banana bread daily for eight weeks – but one contained ground walnuts.
The 64 students were asked to perform a number of cognitive tests, including one to determine the veracity of statements contained in a short narrative, with the walnut group performing better in “inferential reasoning”.
"Students consuming walnuts showed a significant improvement in inference after consuming one-half cup of walnuts daily for eight weeks," said Peter Pribis, lead author and associate professor of nutrition and wellness at Andrews.
"Walnuts will obviously not make you a critical thinker; this comes after years of studying. However, students and young professionals in fields that involve a great deal of critical thinking or decision-making could benefit from regularly eating walnuts."
But he called for further research into the brain health area.
Verbal and non-verbal reasoning
Walnuts, rich in vitamin E, folate, melatonin and the omega-3 linolenic acid, have been more commonly linked in the scientific literature with heart health and antioxidative properties, a body of work strong to win a positive health claim opinion from the European Food Safety Authority (EFSA) recently.
EFSA’s health claims panel found walnut consumption could benefit blood vessel function. That opinion can be found here.
The researchers said the randomised, crossover trial with 18-25 year-olds was the first to test the effect of walnut consumption on verbal and non-verbal reasoning.
“…the authors conclude that non-verbal reasoning seems to be stable enough to not be altered by this nutritional intervention,” they wrote.
“This may be partly explained by the fact that the study population, college students, may be already having high cognitive abilities and so further improvement would be difficult to achieve.”
But inferential thinking had been improved, they said. Inference is the ability to designate the degree of accuracy of conclusions that have been drawn from certain facts.
“The results for inference showed a signiﬁcant improvement after walnut supplementation (P¼0·009; d ¼ 0·567; 11·2 %), but we did not observe any period-speciﬁc effect,” they wrote.
But in calling for more research, they acknowledged they did not understand why inferential thinking was the only parameter that had been improved.
They could not, “explain why inference alone was affected by consumption of walnuts and not the other ‘critical thinking’ subtests – recognition of assumption, deduction, interpretation, and evaluation of arguments.”
British Journal of Nutrition
‘Effects of walnut consumption on cognitive performance in young adults’
Authors: Peter Pribis, Rudolph N. Bailey, Andrew A. Russell, Marcia A. Kilsby, Magaly Hernandez, Winston J. Craig, Tevni Grajales, David J. Shavlik, Joan Sabate.