Mediterranean-Style Diet Linked to Higher Total Brain Volume

More research is suggesting that adherence to a Mediterranean-style diet (MeDi) may be protective for the aging brain.



In a cohort of more than 400 individuals from Scotland who were in their 70s, those who were low consumers of the MeDi had significantly lower total brain volume over a 3-year period than those who regularly adhered to this type of diet.

Interestingly, an increased consumption of fish or lower consumption of red meat did not drive this finding, "suggesting that other components of the MeDi or, possibly, all of its components in combination are responsible for the association," write the investigators.

There were also no significant differences between the groups in changes in gray matter volume or cortical thickness.

"I think our story is adding to the growing evidence that a Mediterranean diet is having positive and possibly protective effects on health," lead author Michelle Luciano, PhD, lecturer at the University of Edinburgh, Scotland, United Kingdom, told Medscape Medical News.

"I'm a diet skeptic but was pleasantly surprised to find that this was a very well-done study," said David S. Knopman, MD, professor of neurology at the Mayo Clinic, Rochester, Minnesota, when invited to comment.

"The fact that they were able to demonstrate an effect on changes in brain volume stands up to a review of the methodology," added Dr Knopman, who was not involved with this research.

The main caveat, however, is that while those who adhered to the MeDi had a slower rate of brain volume loss, there was no difference in the baseline value between the groups, "which the authors themselves acknowledge is a little bit of an inconsistency. And this makes me question whether the result is reproducible or not," he said.

Measurements Over Time
The MeDi calls for fruit, vegetables, cereals, legumes, and olive oil in high quantities, moderate amounts of fish, and a low intake of red meat.

As reported by Medscape Medical News, past research has linked this type of diet to many benefits, including better cognitive function and reduced risk for stroke and dementia. It has also recently been associated with increased cortical thickness and to larger brain volume in older patients.

Dr Luciano noted that this last study looked only at brain measurements at a single time point, whereas their study looked at several time points. "So we could look at change in brain volume over time," she said.

The investigators examined data from the Lothian Birth Cohort of 1936, which is the year all of the participants were born. The original study included 1091 individuals from the Edinburgh region of Scotland who underwent a mental ability test when they were 11 years of age.

For the current analysis, the investigators examined 401 of the participants who filled out the Scottish Collaborative Group Food Frequency Questionnaire (FFQ) at around age 70 years (baseline) and underwent structural MRI approximately 3 and 6 years later (mean age, 72.7 and 76.3 years, respectively).

During these three time points, cognitive assessments were also administered.

A MeDi score was calculated based on the FFQ and ranged from 0 to 9, with a higher score representing greater adherence to the diet. High diet adherence was defined as a score between 5 and 9, with a score of 4 or less signifying low adherence.

Although most of the demographic characteristics were similar, the high-adherence group had significantly more carriers of the APOE ε4 risk allele than did the low-adherence group (33.2% vs 24.4%, respectively; P = .03).

However, none of the participants were diagnosed with Alzheimer's disease, "so disease progression was unlikely having an influence on diet," write the investigators.

Lower Total Brain Atrophy
Results from all models showed significantly lower total brain atrophy between MRI 1 and MRI 2 in the high adherers to the MeDi compared with the low adherers. This included when adjustments were made for age and sex (P = .02), as well as for additional factors, such as body mass index, diabetes, cognitive function, and education (P = .04).

None of the baseline MRI measurements, however, were significantly associated with MeDi adherence. In addition, neither fish nor meat consumption, when examined specifically, was significantly linked to total brain or gray matter volume.

The researchers note several possible reasons for the discrepancy between this latter finding and what other studies have shown, including differences in the type of fish eaten by the participants, such as oily vs white fish, and whether the meat consumed was fresh or processed.

"It might be the case that other specific dietary components have direct functional effects on total brain atrophy, but given the interdependency of [these] components…identifying specific foods and potentially nutrients with such an effect is formidable," write the investigators.

In summary, Dr Luciano noted that "it's important to point out that this is an association study," so the researchers weren't able to ascertain a causal link between diet and brain volume loss.

However, because they measured diet habits 3 years before the first brain volume measurement, "this gives us some suggestion that the diet might be having a protective effect. But future research will need to confirm that before we give recommendations to practitioners."

She added that future studies will also need to assess whether longer adherence to this type of diet is associated with greater effects, including cognitive function.

"We're assuming that people are probably following a similar diet for a long period of time," said Dr Luciano. But because they measured food intake only at one time point, "we just don't have that information."

Potential Bias?
Dr Knopman commented to Medscape Medical News that the biggest limitation is that almost all diet studies, including this one, are observational and subject to potential biases.

"And the main bias is that people who tend to adhere to a healthy diet are also likely to be the ones who exercise more, don't smoke, avoid obesity, and practice other good health behaviors. And those can't be fully controlled for in these types of analyses," said Dr Knopman, adding that diet is just one part of a whole package of important lifestyle habits.

Plus, which component or components of a MeDi that provide benefit is unclear, he said.

"The value of the Mediterranean diet seems good in its generality but the specifics are unknown. And as a scientist, that makes me a little uncomfortable," said Dr Knopman.

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