The Mediterranean Diet Has Varied Effects on Cognitive Decline Among Different Race-Specific Populations

While the Mediterranean diet may have broad health benefits, its impact on cognitive decline differs among race-specific populations, according to a new study published in the Journal of Gerontology.

The team of researchers, including Ben-Gurion University of the Negev (BGU Prof. Danit R. Shahar RD, Ph.D, analyzed an NIH/NIA prospective cohort study [Health ABC] conducted over eight years in the U.S. to measure the effects of adherence to a Mediterranean diet. Prof. Shahar is affiliated with the BGU S. Daniel Abraham International Center for Health and Nutrition, Department of Public Health, Faculty of Health Sciences.

The Mediterranean-style diet (MedDiet) has fewer meat products and more plant-based foods and monounsaturated fatty acids from olive and canola oil (good) than a typical American diet.

To assess the association between MedDiet score and brain function, the researchers used data of several Modified Mini-Mental State Examinations (3MS) on 2,326 participating older adults (70-79). The 3MS is an extensively used and validated instrument designed to measure several cognitive domains to screen for cognitive impairment and commonly used to screen for dementia.

"In a population of initially well-functioning older adults, we found a significant correlation between strong adherence to the Mediterranean diet and a slower rate of cognitive decline among African American, but not white, older adults. Our study is the first to show a possible race-specific association between the Mediterranean diet and cognitive decline.”

The researchers note that further studies in diverse populations are necessary to confirm association between the MedDiet and cognitive decline, and to pinpoint factors that may explain these results.

(Image: Getty Images)

Mediterranean diet seems to boost ageing brain power

A Mediterranean diet with added extra virgin olive oil or mixed nuts seems to improve the brain power of older people better than advising them to follow a low-fat diet, indicates research published online in the Journal of Neurology Neurosurgery and Psychiatry.

The authors from the University of Navarra in Spain base their findings on 522 men and women aged between 55 and 80 without cardiovascular disease but at high vascular risk because of underlying disease/conditions.

These included either type 2 diabetes or three of the following: high blood pressure; an unfavourable blood fat profile; overweight; a family history of early cardiovascular disease; and being a smoker.

Participants, who were all taking part in the PREDIMED trial looking at how best to ward off cardiovascular disease, were randomly allocated to a Mediterranean diet with added olive oil or mixed nuts or a control group receiving advice to follow the low-fat diet typically recommended to prevent heart attack and stroke

A Mediterranean diet is characterised by the use of virgin olive oil as the main culinary fat; high consumption of fruits, nuts, vegetables and pulses; moderate to high consumption of fish and seafood; low consumption of dairy products and red meat; and moderate intake of red wine.

Participants had regular check-ups with their family doctor and quarterly checks on their compliance with their prescribed diet.

After an average of 6.5 years, they were tested for signs of cognitive decline using a Mini Mental State Exam and a clock drawing test, which assess higher brain functions, including orientation, memory, language, visuospatial and visuoconstrution abilities and executive functions such as working memory, attention span, and abstract thinking.

At the end of the study period, 60 participants had developed mild cognitive impairment: 18 on the olive oil supplemented Mediterranean diet; 19 on the diet with added mixed nuts; and 23 on the control group.

A further 35 people developed dementia: 12 on the added olive oil diet; six on the added nut diet; and 17 on the low fat diet.

The average scores on both tests were significantly higher for those following either of the Mediterranean diets compared with those on the low fat option.

These findings held true irrespective of other influential factors, including age, family history of cognitive impairment or dementia, the presence of ApoE protein—associated with Alzheimer’s disease—educational attainment, exercise levels, vascular risk factors; energy intake and depression.

The authors acknowledge that their sample size was relatively small, and that because the study involved a group at high vascular risk, it doesn’t necessarily follow that their findings are applicable to the general population.

But they say, theirs is the first long term trial to look at the impact of the Mediterranean diet on brain power, and that it adds to the increasing body of evidence suggesting that a high quality dietary pattern seems to protect cognitive function in the ageing brain.

Mediterranean diet may not protect brain

Hopes that a Mediterranean diet would be as good for the head as it is for the heart may have been dampened by a French study that found little benefit for aging brains from the diet rich in fruit, vegetables, whole grains, nuts, wine and olive oil.

The study, published in the American Journal of Clinical Nutrition, looked at the participants’ dietary patterns in middle age and measured their cognitive performance at around age 65, but found no connection between Mediterranean eating and mental performance.

"Our study does not support the hypothesis of a significant neuroprotective effect of a (Mediterranean diet) on cognitive function," writes study leader Emmanuelle Kesse-Guyot at the nutritional epidemiology research centre of the French national health research agency INSERM.

It’s been suggested that the “good” fats in the Mediterranean diet might benefit the brain directly, or that low saturated fats and high fiber in the diet could help stave off cognitive decline indirectly by keeping blood vessels healthy.

Previous research has seemed to uphold that premise.

One large study in the US Midwest, for example, found that people in their 60s and older who ate a mostly Mediterranean diet were less prone to mental decline as they aged. Another study of residents of Manhattan linked a Mediterranean-style diet to a 40 per cent lower risk of Alzheimer’s disease.

No significant difference

Researchers in the French study used data on 3083 people who were followed from the mid-1990s, when they were at least 45 years old.

At the beginning of the study, participants recorded what they ate over one 24-hour period every two months, for a total of six dietary record samples per year. Then, between 2007 and 2009 when the participants were about 65 years old, their memory and other mental abilities were measured.

Researchers then separated participants into three categories depending on how closely they adhered to a Mediterranean-style diet, and compared their mental ability test scores.

Overall, they found that people who ate a diet closest to the Mediterranean ideal performed about the same as those who ate a non-restricted diet.

Associate Professor Nikos Scarmeas, of New York’s Columbia University Medical Center, was not involved with the study but has researched the effects of food on brain health. He says it’s important to note that the new study had some limitations.

For instance, researchers only tested the participants’ mental abilities once, making it impossible to track whether they got better or worse over time, adds Scarmeas.

"We don’t have the strong evidence to go and tell people, ‘Listen, if you follow this diet, it will improve cognition’," he says.

(Image: mediterraneandiet.com)