According to a epidemiological study published in The Journal of Nutrition, Health & Aging, eating walnuts may improve performance on cognitive function tests, including those for memory, concentration and information processing speed in adults (ages 20-59 and 60 and older).3 In this retrospective study, cognitive function was consistently greater in adult participants who consumed walnuts, even after adjusting for age, gender, race, education, BMI, smoking, alcohol consumption and physical activity. Analyses are based on single, 24-hour recalls, which reflect one day of intake for the subjects. This cross-sectional study was the first large representative analysis of walnut intake and cognitive function, and the only study to include all available cognitive data across multiple National Health and Nutrition Examination (NHANES) surveys, representing over 10,000 individuals.
A study published in the Journal of the American Medical Association Internal Medicine found that eating a Mediterranean diet supplemented with olive oil or nuts (primarily walnuts) was correlated with reduced age-related decline in cognitive function in an older Spanish population (ages 55-80) at high cardiovascular risk.4 This clinical trial was conducted in a subcohort of the PREvención con DIeta MEDiterránea (PREDIMED) trial. Participants (447 total) were randomly assigned to a Mediterranean diet supplemented with mixed nuts (15g walnuts, or about 0.5 ounces, 7.5g almonds and 7.5g hazelnuts per day), a Mediterranean diet supplemented with extra virgin olive oil (at least 50g or 4 tablespoons per day) or a low-fat diet (control group). The study found that participants who consumed a Mediterranean diet with nuts, including walnuts, showed improvements in memory compared to a low-fat diet.
An animal study published in the Journal of Alzheimer’s Disease demonstrated that a diet including walnuts may have a beneficial effect in reducing the risk, delaying the onset, or slowing the progression of Alzheimer’s disease.5 The research group examined the effects of dietary supplementation with 6 percent or 9 percent walnuts in mice (equivalent to 1 ounce and 1.5 ounces of walnuts per day in humans) compared to a control diet with no walnuts. The study found significant improvement in learning skills, memory, anxiety reduction, and motor development in mice fed a walnut-enriched diet. This research stemmed from a previous cell culture study that highlighted the protective effects of walnut extract against the oxidative damage caused by amyloid beta protein, the major component of amyloid plaques that form in the brains of those with Alzheimer’s disease.6 Findings from animal and cell studies are provided as background and used to formulate hypotheses for additional research needed to determine the effects on humans.
An epidemiological study published in Nutrients demonstrated that consuming walnuts may be associated with reduced depression symptoms among American adults.7 Researchers examined data on 26,656 American adults (ages 0-85 years) from the National Health and Nutrition Examination Survey (NHANES). Those who ate walnuts were more likely to have greater interest in activities, higher energy levels, less hopelessness (for women) better concentration, and greater optimism, compared to those who did not consume nuts. These results held even after controlling for age, sex, race, income, BMI, smoking, alcohol consumption, and marital status. On average, walnut consumers ate about 24 grams of walnuts per day (just shy of a one-quarter cup serving). While the association between nut consumption and lower depression symptoms was consistent for men and women, the effect appeared to be strongest among women, who are more likely to report greater depression symptoms and use of antidepressants, compared to men.
A study published in Nutrients found that walnut consumption may help improve mood in men.8 While maintaining their typical diet, activities and lifestyle habits, participants (college-age men and women) consumed half a cup of walnuts daily for eight weeks. Mood was assessed using a common questionnaire (Profiles of Mood States (POMS)) about key domains such as tension, depression, anger, vigor, fatigue and confusion. The findings showed that non-depressed healthy, young males (ages 18-25) had a 27% reduction in overall mood disturbances. No significant changes in mood were observed in females or when the data was analyzed with both genders included.
