The plant-based Mediterranean diet is an ongoing diet fad, and proponents now have some new ammunition - it is associated with improved cognitive function in a study of older adults in Spain, according to a paper in JAMA Internal Medicine.
A randomized clinical trial included 447 cognitively healthy volunteers (223 women, average age almost 67) who were considered high cardiovascular risk and were enrolled in the Prevencion con Dieta Mediterranea nutrition intervention. Of the participants, 155 individuals were assigned to supplement a Mediterranean diet with one liter of extra virgin olive oil per week; 147 were assigned to supplement a Mediterranean diet with 30 grams per day of a mix of walnuts, hazelnuts and almonds; and 145 individuals were assigned to follow a low-fat control diet.
The authors measured cognitive change over time with a battery of neuropsychological tests and they constructed three cognitive composites for memory, frontal (attention and executive function) and global cognition. After a median of four years of the intervention, follow-up tests were available on 334 participants.
At the end of the follow-up, there were 37 cases of mild cognitive impairment: 17 (13.4 percent) in the Mediterranean diet plus olive oil group; eight (7.1 percent) in the Mediterranean diet plus nuts group; and 12 (12.6 percent) in the low-fat control group. No dementia cases were documented in patients who completed study follow-up.
The study found that individuals assigned to the low-fat control diet had a significant decrease from baseline in all composites of cognitive function. Compared with the control group, the memory composite improved significantly in the Mediterranean diet plus nuts, while the frontal and global cognition composites improved in the Mediterranean diet plus olive oil group. The authors note the changes for the two Mediterranean diet arms in each composite were more like each other than when comparing the individual Mediterranean diet groups with the low-fat diet control group.
Would those who got impairment without the diet have prevented it with the diet? The study is far too small to make that determination but other studies have linked dietary habits and cognitive performance - there are even whole diets based on such "brain food", though no true studies have validated it. Oxidative stress (the body's inability to appropriately detoxify itself using mitochondria or other cellular action) has long been considered to play a major role in cognitive decline. Some studies suggest following a Mediterranean diet may relate to better cognitive function and a lower risk of dementia. However, the observational studies that have examined these associations have limitations, according to the study background.
"Our results suggest that in an older population a Mediterranean diet supplemented with olive oil or nuts may counter-act age-related cognitive decline. The lack of effective treatments for cognitive decline and dementia points to the need of preventive strategies to delay the onset and/or minimize the effects of these devastating conditions. The present results with the Mediterranean diet are encouraging but further investigation is warranted," the study concludes.
Citation: JAMA Intern Med. May 11, 2015. doi:10.1001/jamainternmed.2015.1668