Results of a randomized clinical trial, published earlier this month in the JAMA Internal Medicine, revealed that long-term consumption of the Mediterranean diet supplemented with either extra virgin olive oil or nuts improved cognitive function in older adults.
Although previous observational studies reported a positive relationship between adherence to the Mediterranean diet and improved cognitive function, they compared intake of a control diet versus intake of a Mediterranean diet without a baseline evaluation of the subjects before and after consumption of the Mediterranean diet.
In contrast, findings of the new study are based on repeated neuropsychological assessment of the subjects who consumed a control diet or a Mediterranean diet supplemented with either EVOO or nuts over a four-year period.
Conducted on a small sub-sample of Spanish subjects enrolled at the Barcelona-North PREDIMED center, the study started with 447 cognitively healthy subjects who had either Type 2 diabetes or risk to cardiovascular disease in 2003. However, only 344 subjects completed the study in 2009. The objective of the study was to investigate the effect of an antioxidant-rich Mediterranean diet on cognitive function of the subjects.
The enrolled subjects were randomly assigned to one of the three diets: a Mediterranean supplemented with one liter of extra virgin olive oil per week; a Mediterranean supplemented with intake of 30 grams mixed nuts that included 15 grams of walnuts, and 7.5 grams each of almonds and hazelnuts; or a control diet with advice to reduce fat intake.
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Cognitive function of the subjects, whose average age was 67 years, was assessed by several neuropsychological tests that were carried out at the beginning of the study to provide baseline data and again, at the end of the study. Three cognitive composites were constructed from the neuropsychological tests that included memory composite (based on the Rey Auditory Verbal Learning Test and the Welchler Memory Scale); frontal composite that measured attention, cognitive flexibility and working memory; and global composite that assessed changes in all neurological tests conducted.
At the end of the study, results revealed that subjects on both variations of the Mediterranean diet had improved cognitive function while those on the control diet showed a decline in cognitive function. Furthermore, the investigators found that the observed changes were consistent in all subjects irrespective of factors such as gender, age, energy consumption, and other variables.
More specifically, results showed a significant increase in memory composite in the group who consumed a Mediterranean diet supplemented with nuts, while those on the Mediterranean diet with olive oil improved frontal and global cognition composites.
Increased intake of antioxidant and anti-inflammatory agents that are naturally present in the Mediterranean diet may be responsible for improving cognitive composites of the subjects, according to the authors of the study.
In addition, the phenolic-rich compounds in extra virgin olive oil and nuts may also be protective against neurodegeneration as they act as antioxidants, increase blood flow to the brain and increase neuron synthesis.
In spite of several drawbacks of the study such as a small sample size recruited from a larger study with different objectives, results of the study showed that the Mediterranean diet supplemented with olive oil or nuts protected against cognitive decline.
In an interview for JAMA Network, Emilo Ros, MD, PhD, senior consultant at the Endocrinology Department, Hospital Clinic de Barcelona, said, “The two Mediterranean diets counteracted age-related cognition decline compared to the control diet.”
Ros further emphasized the importance of this study as the first randomized clinical trial and suggested that intervention with Mediterranean diet supplemented with EVOO or nuts at the pre-clinical stage would be beneficial before the onset of development of memory complaints and cardiovascular health problems.