By David Kiefer, MD
Clinical Assistant Professor, Department of Family Medicine, University of Wisconsin; Clinical Assistant Professor of Medicine, Arizona Center for Integrative Medicine, University of Arizona, Tucson
Dr. Kiefer reports he is a consultant for WebMD.
SYNOPSIS: Higher adherence to the Mediterranean diet led to measurable increases in brain volume in a multi-ethnic sampling of older adults.
SOURCE: Gu Y, et al. Mediterranean diet and brain structure in a multiethnic elderly cohort. Neurology 2015 Oct 21. pii: 10.1212/WNL.0000000000002121.
Summary Points
- The researchers analyzed the diet of a diverse elderly population without dementia.
- People consuming five or more Mediterranean diet foods had a greater brain volume than those consuming four or less Mediterranean diet foods, equivalent to about 5 years of brain aging.
- The brain volume benefits were most strongly associated with higher fish intake, lower meat intake, and moderate alcohol intake.
Can the Mediterranean diet, with its accumulating evidence for cardiovascular protection, cancer prevention, and anti-inflammatory effects, also benefit the human cerebrum? The authors of this analysis previously published research showing a decreased incidence of Alzheimer’s disease with adherence to a Mediterranean diet, but other results weren’t convincing, likely due to a variety of confounding variables. Here, the authors strived to clarify the brain effects of a Mediterranean diet through a prospective, cross-sectional study that utilized advance neuroimaging techniques sensitive for an aging brain’s changing structure.
This analysis was done on 2776 elderly (> 65 years of age) people without dementia receiving Medicare benefits in northern Manhattan. This cohort was an ongoing prospective study on aging and dementia, known by the acronym WHICAP. At baseline, physicians completed a physical exam and neurological history and assessed cognitive function using a “battery” of neuropsychological tests for each participant. These examinations were repeated every 18 months, at which time a diagnosis of dementia was made if criteria were met based on the DSM-III-R. Further criteria were used to determine the type of dementia, and the Clinical Dementia Rating scale was used to establish dementia severity.
Of this cohort, magnetic resonance imaging (MRI) data were available for 769 people, a subgroup that tended to be younger, African American, and male compared to the original cohort. Complete images were unavailable for 45 participants, 10 participants did not have dietary data available, and 40 participants were diagnosed with dementia at the time of the MRI scan, leaving 674 participants for analysis in this study. Table 1 describes the MRI information collected, including global brain measures, regional cortical volume analyses, and mean cortical thicknesses across 34 regions of interest.
Table 1: Study Randomization |
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Category of MRI Data |
Examples |
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Global brain measures |
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Regional cortical volume analyses |
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Mean cortical thickness |
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At an average of 0.6 years before the MRI scan, the Willett’s semi-quantitative food frequency questionnaire was used to collect information about each participant’s average diet over the previous year. This diet information was then scored to determine adherence to a Mediterranean diet; one point was awarded for each of a variety of parameters (considered “beneficial food components”) as delineated in Table 2 for a total score (9 points maximum). In addition, sub-group analyses were undertaken to determine the contribution of each of the nine different food groups to the observed MRI differences.
Table 2: How to Earn 1 Point for a “Beneficial Food Component” in the Mediterranean Diet Scoring When the FFQ Was Analyzed |
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The total cohort (n = 674) had a mean age of 80.1 years, and was 67% female, 28% white, 35% black, and 36% Hispanic. The group was split into high adherence to the Mediterranean diet for scores 5-9 (n = 304) and low adherence to the Mediterranean diet for scores 0-4 (n = 370). The two Mediterranean diet adherence groups were statistically identical with respect to baseline demographics, past medical history (stroke, diabetes, hypertension, heart disease), body mass index, and cognitive scores on neuropsychiatric testing.
With respect to outcome variables, the two Mediterranean diet adherence groups were compared relative to MRI findings. The high vs low Mediterranean diet adherence group had similar cortical thicknesses (2.46 mm vs 2.45 mm, respectively, P = 0.44), whereas the higher Mediterranean diet adherence group had larger brain volumes (total brain volume [TBV], total gray matter volume [TGMV], and total white matter volume [TWMV]), all statistically significant when adjusted for intracranial volume (ICV). (See Table 3.) The authors were able to calculate that one additional year of age corresponded to the loss of 2.62 mL of TBV (P < 0.0001). From this calculation, the researchers were able to conclude that high Mediterranean diet adherence groups had about five years’ more brain volume than the low adherence group. Worded another way, a high adherence to an Mediterranean diet staved off brain aging by 5 years compared to a low adherence to an Mediterranean diet.
Table 3: Brain Volumes for High vs Low Adherence to Mediterranean Diet When Adjusted for ICV |
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Low MEDDIET Adherence |
High MEDDIET Adherence |
Low MEDDIET Adherence when Adjusted for ICV |
High MEDDIET Adherence when Adjusted for ICV |
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TBV (mL) |
865 |
878 |
-6.5 |
7.9 (P = 0.003) |
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TGMV (mL) |
517 |
522 |
-2.9 |
3.6 (P = 0.017) |
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TWMV (mL) |
372 |
379 |
-3.6 |
4.4 (P = 0.016) |
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MEDDIET: Mediterranean diet; TBV: total brain volume; TGMV: total gray matter volume; TWMV: total white matter volume; ICV: intracranial volume |
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Furthermore, t-tests and chi-squared statistical analyses allowed the researchers to conclude that the individuals with higher TBV, TGMV, and TWMV tended to be younger, male, less likely to have diabetes, less likely to have dementia, and to have lower body mass index and better cognition.
With respect to specific foods, higher fish intake, lower meat intake, and moderate alcohol intake were associated with higher TBV, TGMV, and TWMV. Quantifiably, one could achieve protection from 3-4 years of brain atrophy but consuming at least 3-5 ounces of fish weekly or limiting meat consumption to 100 g weekly. Fish intake was also the one variable that affected cortical thickness and was associated with increased thickness; other variables, including the Mediterranean diet as a whole, did not change cortical thickness. Regionally, the cingulate, parietal, temporal, and hippocampus volumes most accounted for the high vs low MEDDIET adherence differences.
COMMENTARY
This study lets the scientific and medical communities add a feather to the cap of the Mediterranean diet. The Mediterranean diet will protect you, among other things, from cardiovascular disease,1 diabetes,2 Alzheimer’s disease,3 and, as we now learn from this study, will provide quantifiable changes to cerebral structure that have dementia correlates. Furthermore, some previous studies had limited demographic and ethnic diversity, limiting the generalizability of the results. In this case, with a relatively even split between Caucasian, African American, and Latino, many health care providers might see a direct relevancy to the patients in their clinical practice.
In some respects, these results are nothing new. Prior clinical trials have convincingly found associations between diet and cognitive function, even prevention of the ultimate ramification of cognitive decline, Alzheimer’s disease.3,4,5 It’s the how that had been missing. I can imagine a day when we are discussing dietary change with our patients that we show before and after brain MRI images as a motivator: “Incorporate more vegetables and fish into your diet, and your brain will look like this in 5 years.” That’s hard to ignore.
A few minor points are lacking here, and leave clinicians wondering. It is difficult to ascertain how long someone needs to eat the Mediterranean diet foods to achieve the results here. The statistical associations were analyzed at different time points in this longitudinal cohort, so some clarification on the time course would have been helpful. Also, although these patients were dementia-free, and the study was organized in that way, it would have made sense to weave in the incidence of dementia as the trial progressed to then correlate brain volumes not only with Mediterranean diet adherence but subsequent development of dementia. Such a methodology would have created a more cohesive clinical story. Furthermore, the significance of the regional changes in brain volume is vague and went mostly unexplained, though it can be argued that such a deficit is more representative of the current state of our neurological knowledge than it is of the researchers’ oversight. I would predict a honing of the specificity between diet and brain function/structure in the years to come.
Nonetheless, the breadth and depth of information collected was impressive and allowed for some interesting quantifications, the equivalent of “years of brain volume saved.” Overall, given the findings here, there is little reason to not recommend a Mediterranean diet to our patients that fall into this age group. Clinicians can confidently say such a dietary approach will have wide-ranging benefits, not the least of which is a clear-cut improvement in brain volume loss, mostly considered to be an inevitable result of the aging process. Not anymore!
REFERENCES
- Estruch R, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013;368:1279-1290.
- Salas-Salvado J, et al. Prevention of diabetes with Mediterranean diets: A subgroup analysis of a randomized trial. Ann Intern Med 2014;160:1-10.
- Morris MC, et al. MIND diet associated with reduced incidence of Alzheimer’s disease. Alzheimers Dement 2015;11:1007-1014.
- Tsivgoulis G, et al. Adherence to a Mediterranean diet and risk of incident cognitive impairment. Neurology 2013;80:1684-1692.
- Tangney CC, et al. Relation of DASH- and Mediterranean-like dietary patterns to cognitive decline in older persons. Neurology 2014;83:1410-1416.
Higher adherence to the Mediterranean diet led to measurable increases in brain volume in a multi-ethnic sampling of older adults.
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