A new study by researchers at three universities and several medical institutions in Spain has linked a Mediterranean diet supplemented with olive oil or nuts to better cognitive function in older people than was associated with a low-fat diet, after a 6½ year period on the diets.
The study, conducted by Professor Miguel A Martinez-Gonzalez, at the Medical School of the University of Navarra, and colleagues, was published on May 13, 2013 in the Journal of Neurology, Neurosurgery and Psychiatry.
The Study; Method
The researchers recruited a group of 522 older Spanish men and women (average age 75 on follow-up testing), all of whom were at increased risk of cardiovascular events. Forty-five percent of the participants were men, and 55% were women.
The participants were randomly assigned to three groups: (1) 244 participants – to a group that consumed a Mediterranean Diet supplemented with olive oil (“Med + Olive Oil Diet”), (2) 166 participants to a group that consumed a Mediterranean Diet supplemented with nuts (“Med + Nuts Diet”), and (3) 132 participants – to a control group that consumed a low-fat diet (“Low Fat Diet”).
After 6.5 years of this nutritional intervention, all of the participants underwent cognitive testing to assess their global cognitive performance. The tests included the standard Mini-Mental State Examination (MMSE) and the Clock Drawing Test (CDT). The researchers who assessed the outcome were blinded to group assignment of the participants.
The researchers found that participants allocated to the Med + Olive Oil Diet showed significantly higher cognitive performance, measured by their mean MMSE and CDT scores, after 6.5 years on the Med + Olive Oil Diet than the control group eating the Low Fat Diet over the same period (adjusted differences: +0.62 95% CI +0.18 to +1.05, p=0.005 for MMSE, and +0.51 95% CI +0.20 to +0.82, p=0.001 for CDT).
Participants in the Med + Nuts Diet group also tested with higher cognitive function, measured by their MMSE and CDT scores, after 6.5 years on the Med + Nuts Diet than the control group on the Low Fat Diet over the same period (adjusted differences: +0.57 (95% CI +0.11 to +1.03), p=0.015 for MMSE and +0.33 (95% CI +0.003 to +0.67), p=0.048 for CDT).
These findings were made after adjustment for possible confounding factors, including sex, age, education, Apolipoprotein E genotype, family history of cognitive impairment/dementia, smoking, physical activity, body mass index, hypertension, dyslipidaemia, diabetes, alcohol and total energy intake. The researchers also reported that the results did not differ after controlling for incident depression.
The study authors concluded that “An intervention with MedDiets enhanced with either EVOO [olive oil] or nuts appears to improve cognition compared with a low-fat diet.”
“Our trial suggests that nutritional intervention with MedDiet supplemented with either extra-virgin olive oil or nuts is associated with improved global cognition,” the authors further stated.
“There are mechanisms that can explain the protective effect of MedDiet on cognitive status, including antioxidative and anti-inflammatory effects and reduced vascular comorbidities,” the authors wrote.
According to the authors, “Oxidative stress has been associated with neurodegeneration. The main components of the MedDiet intervention … extra-virgin olive oil and nuts, have antioxidant properties and, together with other polyphenol-rich foods in the MedDiet, are suggested to relate to improved cognitive function.”
However, the authors cautioned that their study design created limitations, making it difficult to generalize from their findings. They did not test cognitive function of the participants at baseline, and also did not control for depression at baseline or cognitive assessment. In addition, the sample size was relatively small, and true “double-blind, long-term trials” are not possible when studying nutrition, they observed.
Finally, the study included only participants at high risk of cardiovascular disease, making it “uncertain” whether the findings could be generalized to the average general population, the researchers noted.
“Future interventional research including both baseline and follow-up assessments of global and multiple domains of cognition is needed to obtain firmer evidence regarding potential benefits of MedDiet on cognition,” the authors concluded.
It should also be noted that in their potential conflict of interest disclosures, certain of the researchers reported ties to companies and organizations including Cerveceros Espana, Nut and Dried Fruit Foundation, the Scientific Advisory Committee of the California Walnut Commission, sanofis aventis, FIVIN-Spain, Novartis, Biogen, Teva, sanofi aventis, Lundbeck and Bayer, UCB Pharma, GlaxoSmithKline, Lundbeck, Esteve, Flora Foundation, Roche, AMGEN, Merck, DAMM, Abbott, Takeda, Sankyo, Nutrexpa, Feiraco, Unilever UK, Ferrer International, KARO-BIO, DANONE, PACE, AstraZeneca, Rottapharm, and Ricordati, some of which may have economic interests served by promoting the sale of nuts or olive oil, or foods or supplements associated with the Mediterranean Diet.
Another study, conducted by researchers at the University of Alabama and University of Athens, Greece, involving 17,478 participants, recently found that eating foods high in omega-3 fatty acids can help preserve memory and cognitive functions, but only in people without diabetes.
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