In a recent review published in Frontiers in Nutrition, the researchers reviewed studies linking olive oil consumption to cognitive performance .
Dietary interventions to improve cognition
As life expectancy rises, there is an increasing number of elderly people, many of whom struggle with cognitive decline. However, current treatments for age-related cognitive decline are limited, and so there has been ongoing research into preventing or delaying those processes. Dietary interventions seem to be a promising and easy-to-implement avenue .
The authors of this review have proposed that the Mediterranean diet may have the potential to improve cognition , as it has been reported to reduce the likelihood of suffering from neurodegenerative diseases .
One of the key components of the Mediterranean diet is extra-virgin olive oil. Previous work has linked frequent olive oil consumption and improvements in cognitive function. It is also suggested that olive oil consumption can help with dementia prevention .
In this review, the researchers analyzed clinical trials, cohort studies, and cross-sectional studies to determine the role of olive oil consumption on cognitive functions in people over 55.
Clinical trials were largely positive
In a randomized, controlled trial conducted in Greece, participants who received high-phenolic, early-harvest, extra-virgin olive oil outperformed people who received moderate-phenolic, extra-virgin olive oil or participants who only received instructions for the Mediterranean diet in almost all cognitive tests .
Similar results were obtained in a clinical trial performed in Spain . In this study, the group that consumed the Mediterranean diet and extra-virgin olive oil “exhibited superior performance on all cognitive domains measured” compared to people who consumed the Mediterranean diet plus nuts or an ordinary low-fat diet.
At the end of the 6.5-year follow-up period, a mild cognitive impairment diagnosis was confirmed among 7.8% of people who ate the Mediterranean diet with extra-virgin olive oil. For the groups eating Mediterranean diet with nuts or a low-fat die, it was 11.8% and 19.3%, respectively, suggesting a protective role of olive oil against mild cognitive impairment.
A third randomized, controlled trial was performed in Italy . Study groups were given a plain Mediterranean diet or a Mediterranean diet enriched with olive oil for one year. The researchers found improvements in the Alzheimer’s Disease Assessment Scale’s cognitive subscale, which measures several cognitive abilities, such as memory and language, in both study groups. However, they didn’t report significant differences in other tests.
Cross-sectional studies showed different results
Cross-sectional studies did not always agree with the results of the randomized, controlled trials. In one from Greece, the authors used the Food Frequency Questionnaire to evaluate the participants’ diets. This analysis didn’t find a significant relationship between the consumption of olive oil and cognitive health .
A Spanish cross-sectional study used the Rey Auditory Verbal Learning Test (RAVLT), “a well-recognized measure of a person’s ability to encode, combine, store and recover verbal information in different stages of immediate memory” . The results of this study suggested an association between total olive oil and virgin olive oil consumption and improved cognitive functions .
Similar results were obtained in a Polish study, which used different tests to measure cognitive functions , and in a study conducted in Morocco, where olive oil was the only dietary component of the Mediterranean diet that has shown protection against cognitive impairment .
Cohort studies were mixed
In a study conducted in France, participants were divided into three groups based on olive oil consumption as reported on the Food Frequency Questionnaire: none, moderate (used for either dressing or cooking), and intensive (used for dressing and cooking). Cognitive tests indicated that, compared to people who didn’t consume olive oil, moderate and intensive olive oil consumption lowers the odds of cognitive impairment in verbal fluency and visual memory. However, the researchers didn’t observe any relationship regarding global cognitive functioning .
The Food Frequency Questionnaire also assessed olive oil intake among participants in a Greek cohort study. Cognitive tests performed after 6 to 13?years of follow-up indicated a non-significant association between the consumption of olive oil and cognitive functioning .
A study of Spanish adults that assesses diet and cognition with six and eight-year follow-up periods concluded that “Participants with low or moderate olive oil consumption demonstrated a larger cognitive decline over the measurement period than those with higher consumption” .
On the other hand, a study conducted in Germany that followed participants for over 10 years didn’t find an association between higher olive oil consumption and lower risk of Alzheimer’s disease or memory decline .
Limitations of heterogeneous data
The studies included in this review were heterogeneous in their designs, ways of reporting olive oil intake, and reported outcomes. This prevented the review authors from conducting meta-analyses or sub-group analyses.
Additionally, some reported studies lacked data regarding participants and the intake of different food groups. The authors also mention that the food intake data in the included cross-sectional and cohort studies relied on self-reported intake reported in Food Frequency Questionnaires. The authors question the reliability of this data. This applies especially to elderly people with cognitive impairment, who might not precisely remember their food intake.
The authors were also concerned about the lack of study protocol registration, which might result in bias. Additionally, their bias analysis indicated a “considerable risk of bias” in half of the randomized, controlled trials. Considering this, the authors call for high-quality clinical trials to strengthen the data about olive oil consumption and cognitive impairments.
Despite the limitations, the authors concluded that:
“Despite some heterogeneity in the findings, the results of the 11 studies were reasonably consistent. The findings from the RCTs indicated that the consumption of olive oil could increase cognitive performance in almost all cognitive domains measured.“
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