A study from Spain published in the Journal of the American Medical Association suggests that a Mediterranean diet supplemented with olive oil or mixed nuts (primarily walnuts) may counter age-related decline in cognitive function.
Combined with evidence from previous studies,1 the results suggest that the plant-forward, antioxidant-rich Mediterranean diet may afford many health benefits, including counteracting age-related cognitive decline. Cognitive decline is a strong risk factor for the development of dementia.
As you’ve likely already heard, the Prevención con Dieta Mediterránea (PREDIMED) study, led by researcher Emilio Ros, MD, PhD, reported that a Mediterranean diet supplemented with extra virgin olive oil or mixed nuts—specifically, a mix comprised of 15 grams of walnuts, 7.5 grams of hazelnuts and 7.5 grams of almonds—for 5 years may contribute to the reduced incidence of cardiovascular disease in high risk individuals.2
The test involved 447 Spanish participants, of whom 113 (25.3%) did not complete the study. The participants included men aged 55-80 and women aged 60-80 at high cardiovascular risk, as well as with either Type 2 diabetes mellitus or at least 3 of 5 cardiovascular risk factors: smoking, hypertension, dyslipidemia, overweight or obesity, or a family history of early-onset coronary heart disease. The subcohort of The Prevención con Dieta Mediterránea (PREDIMED) trial were randomly assigned to a Mediterranean diet supplemented with either extra virgin olive oil (1 liter/week), the nut mixture (30 grams/day), or a control diet (advice to reduce dietary fat), and administered tests at the 4.1 year median follow-up to measure rates of cognitive change.
The results further support findings from previous PREDIMED substudies that suggest cognitive performance was improved following the two Mediterranean diet interventions.3-4
Compared to the control group, test results suggest that participants in the nut cohort showed improvements in memory, while those assigned to the olive oil group had improved frontal function and global cognition.
Oxidative stress has long been considered to play a major role in cognitive decline and neurodegenerative disorders.5 Knowing this, it is plausible that antioxidant-rich foods may protect against neurodegenerative disorders by countering oxidative stress.
The study’s limitations include the fact that it was a post hoc analysis of a subsample of a larger clinical trial that was not designed to examine cognition, and that the overall sample size was small. Also, because of the differential results for the Mediterranean diet on cognitive composites, it is difficult to delineate what part of the diet was associated with preventing cognitive decline. There were losses to follow up, mostly in the control group, and participants who withdrew had worse baseline cognition, thus being more likely to disclose cognitive impairment during follow-up. Given the long recruitment period, intervals of the cognitive assessments were unavoidably unequal. Lastly, the cohort was selected for high vascular risk, which prevents generalizing the results to the average elderly population.
The study also boasts strengths, however, such as the randomized design, long duration, assessment of diet adherence by objective biomarkers and the use of a comprehensive battery of standardized neuropsychological tests to assess cognitive function.
The researchers suggest that the beneficial effects of olive oil and mixed nuts, primarily walnuts, observed probably stems from their antioxidant and anti-inflammatory properties, which when used in conjunction with overall dietary pattern, might afford protection from neurodegenerative diseases. While the present results are encouraging, researchers acknowledge that further investigation is warranted. The study’s results were published online by the Journal of the American Medical Association.6
Resources:
1 Healthy Aging Research. California Walnuts. Available at https://walnuts.org/health-professionals/areas-of-study/list/category/healthy-aging-research/
2 Sala-Vila A, Guasch-Ferré M, Hu FB, et al. Dietary α-linolenic acid, marine ω-3 fatty acids, and mortality in a population with high fish consumption: findings from the PREvención con DIeta MEDiterránea (PREDIMED) study. J Am Heart Assoc. 2016;5(1):e002543.
3 Valls-Pedret C, Lamuela-Raventós RM, Medina-Remón A, et al. Polyphenol-rich foods in the Mediterranean diet are associated with better cognitive function in elderly subjects at high cardiovascular risk. Journal of Alzheimer’s Disease. 2012; 29(4):773-782.
4 Willis LM, Shukitt-Hale B, Joseph JA. Modulation of cognition and behavior in aged animals: role for antioxidant- and essential fatty acid–rich plant foods. American Journal of Clinical Nutrition, 2009; 89(suppl):1602S-1606S.
5 Abha Chauhan. Dietary Supplementation of Walnuts Improves Memory Deficits and Learning Skills in Transgenic Mouse Model of Alzheimer’s Disease. Journal of Alzheimer’s disease. October 2014; 42(4): 1397-1405.
6 Valls-Pedret C, Sala-Vila A, Serra-Mir M, et al. Mediterranean diet and age-related cognitive decline: a randomized clinical trial. JAMA Intern Med. Published online May 11, 2015. doi:10.1001/jamainternmed.2015.1668.