Food for Thought: The Role of Walnuts in Cognitive Function and Healthy Aging
Research on the role of diet on brain health continues to evolve. Limited evidence suggests that eating a diet containing a variety of vegetables, fruits, nuts, beans, and seafood during adulthood is associated with lower risk of age-related cognitive impairment, dementia, and Alzheimer’s disease.1 Although there is no way to prevent diseases such as dementia and Alzheimer’s disease, people of all ages can take steps to improve overall health and well-being. Below is a summary of recent research on healthy aging and cognitive function supported by the California Walnut Commission.
- Walnuts and Physical Function - Findings published in the Journal of Nutrition suggest that consumption of 1-2 servings of walnuts per week (1/4 cup per serving) was associated with reduced risk of developing impairments in physical function in older women, which may help to maintain independence throughout the aging process. Researchers looked at data from 54,762 women in the Nurses’ Health Study, which tracked women for over 30 years. This paper emphasized that overall diet quality, rather than individual foods, may have a greater impact on reducing risk of physical function impairments. Specifically, diet quality traits most associated with reduced rates of incident physical impairment were higher intake of fruits and vegetables; lower intake of sugar-sweetened beverages, trans fat, and sodium; and moderate alcohol intake. Among food components, the strongest relations were found for increased intakes of oranges, orange juice, apples, pears, romaine or leaf lettuce, and walnuts. Study limitations should be considered. The sample only included women, so these results may not be generalizable to men. Additionally, participants were not assigned to eat walnuts or other foods, and were just asked about their dietary choices. It is also possible that subjects may have misreported their dietary intake since this information was collected by questionnaires. In addition, because this is an observational study, residual confounding cannot be ruled out (i.e. that other lifestyle habits which are more common in adults who eat walnuts could contribute to the study findings); and, thus, the results should be interpreted with caution.
- Walnuts and the Fight Against Alzheimer’s Disease - An animal study published in the Journal of Alzheimer’s Disease found that a diet including walnuts may play a role in reducing the risk of Alzheimer’s disease. Researchers examined the effects of dietary supplementation with 6% or 9% 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 ability, memory, reducing anxiety, and motor development in mice fed a walnut-enriched diet. Since this study was performed on animals, findings cannot yet be correlated to humans. Animal studies are provided as background and used to formulate hypotheses for additional research needed to determine the effects on humans.
- Walnuts and Memory – According to a study published in The Journal of Nutrition, Health & Aging, eating walnuts was associated with improved performance on cognitive function tests, including those for memory, concentration and information processing speed. Participants included adults ages 20-59 as well as 60 and over. Cognitive function was consistently greater in adult participants that consumed walnuts, regardless of age, gender or ethnicity. Given this was an observational study, the findings cannot prove causality and there may have been underlying differences between the study groups. The findings are based on single 24 hour recalls, which reflect only one day of food intake. Additionally, the presence of an effect in studies of older individuals, but not among young college students, might reflect a greater vulnerability in older subjects and therefore a greater potential benefit.
- Mediterranean Diet and Cognition - Eating a Mediterranean diet supplemented with olive oil or nuts (primarily walnuts) may reduce the risk of age-related cognitive decline in an older population, according to a study published in the Journal of the American Medical Association Internal Medicine. Participants, a subcohort of the Prevención con Dieta Mediterránea (PREDIMED) trial, were randomly assigned to a Mediterranean diet supplemented with mixed nuts (15g walnuts, 7.5g almonds and 7.5g hazelnuts per day) or 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 control diet. Study limitations to consider are that this is an analysis of a subsample in a larger clinical trial that was not specifically designed to examine cognition and the overall sample size was small. Due to of the differential results for the Mediterranean diet on cognitive composites, it is difficult to precisely delineate what part of the diet was associated with preventing cognitive decline. Researchers experienced losses to follow-up, predominantly in the control group, probably because participants did not receive food incentives. Given the long recruitment period, intervals of follow-up cognitive assessments were unavoidably unequal. Additionally, the cohort was selected for high vascular risk, which prevents generalizing the results to the average elderly population.
1 2015 Dietary Guidelines Advisory Committee: Systematic Reviews of the Dietary Patterns, Foods and Nutrients, and Health Outcomes Subcommittee