Confronted with the highest rates of cognitive decline and dementia in history, (a staggering 47.5 million worldwide with Alzheimer’s, with 9.9 million new cases each year), losing one’s mental capacity is one of the biggest fears in the aging population, according to surveys conducted in the United States and Australia.
Though age is a significant risk factor, researchers have been exploring the synergistic effects of whole dietary patterns as an influence on brain health. According to a study published by Knight, Bryan, and Murphy in Ageing Research Reviews, 2016, rather than isolated foods and ingredients, it has now become more apparent that “the combined, interrelated actions of multiple food components within whole dietary patterns are thought to bring about unique synergistic, additive, and interactive effects in the brain.”
The Mediterranean diet (MedDiet) has long been considered one of the world’s healthiest dietary patterns, so researchers Knight, Bryan, and Murphy set out to review the evidence surrounding the MedDiet, along with the contemporary Western diet, and their associations with age-related cognitive decline. They also sought to determine if it could be a feasible intervention strategy to recommend the MedDiet to those currently consuming a Western dietary pattern.
Obesity is associated with a 70 – 100% increased risk of dementia. It is fairly well established that the Western diet is a major contributor to the growing rates of obesity. The authors suggest that “it is now becoming evident that the clinical problems related to obesity are translating to effects on brain physiology and function.” There is also a consensus that particular nutrients such as saturated, trans fats and refined sugars contribute to age-related cognitive function and neurodegenerative disease via biological mechanisms including inflammation, oxidative stress, and insulin resistance.
As far as an association between the MedDiet and cognitive decline, several longitudinal, three cross-sectional, and two randomized trials assessed in the review did show a general consensus that adhering to a MedDiet improves mild cognitive impairment, Alzheimer’s and dementia. However, due to the nature of the majority of the longitudinal studies being performed in the same cohort of participants, the authors suggest that these results may not be applicable to the wider population.
The two randomized control trials, the only two in this area to date, have shown that consuming a MedDiet with extra virgin olive oil (EVOO) does, in fact, improve cognitive function.
The first trial published in the Journal of Neurology, Neuroscience & Psychiatry, 2013, selected 552 participants with cardiovascular disease to conduct a 5 year trial with a mean follow-up of 6.5 years. Participants were randomized to a low-fat diet or a MedDiet supplemented with EVOO or mixed nuts. The MedDiet group had significantly higher global cognitive scores compared to the low-fat group.
The second trial, published in JAMA Internal Medicine, 2015, selected 447 participants with high cardiovascular risk who were randomly allocated to either a MedDiet supplemented with EVOO; MedDiet supplemented with mixed nuts; or a control low-fat diet. Participants were required to undergo a series of cognitive tests 4.1 years after the intervention. Overall the MedDiet+EVOO scored significantly higher for two of the tests compared to both groups. The MedDiet+EVOO group and MedDiet+mixed nuts saw significant respective changes from baseline in memory, frontal (attention and executive functions), and global function compared to the control group.
Though there are likely many synergistic effects of the MedDiet in its influence on improved cognitive function, researchers claim that the inclusion of olive oil, particularly because of it’s high levels of caffeic acid and tyrosol, reduces markers of inflammation in the central nervous system and has the ability to suppress neuroinflammation in the brain.
Overall the research does suggest that a MedDiet is the best strategy to recommend to people who want to decrease their rate of cognitive decline, Alzheimer’s, dementia, or mild cognitive impairment. Still, while this may be the case, researchers do suggest that due to socio-cultural values, norms, food availability, cost, palatability, and food access, getting people to change their dietary patterns can often be difficult to achieve. They suggest that a more “Westernized” MedDiet intervention could be a more feasible long-term approach worth exploring in future research.