Reference
Luciano M, Corley J, Cox SR, et al. Mediterranean-type diet and brain structural change from 73 to 76 years in a Scottish cohort. Neurology. 2017;88(5):449-455.
Participants
Participants in this study were drawn from the Lothian Cohort of 1936, a group of 1,091 participants born in 1936 in Edinburgh, Scotland. They were 70 years old at this study’s start. Dietary data were collected via mailed questionnaires. Three and then 6 years later, able and willing participants underwent structural magnetic resonance imaging (MRI) brain scans.
Outcome Measures
Two longitudinal brain volumes (total and gray matter; n=401 and 398, respectively) plus a longitudinal measurement of cortical thickness (n=323) were measured. Adherence to the Mediterranean diet was calculated from data gathered from a food frequency questionnaire at age 70, 3 years before the baseline imaging data collection.
Key Findings
Lower adherence to the Mediterranean diet was associated with greater 3-year reduction in total brain volume (explaining 0.5% of variance, P<0.05). Lower adherence to the Mediterranean diet in an older Scottish cohort is predictive of total brain atrophy over a 3-year interval. Fish and meat consumption does not drive this change, suggesting that other components of the Mediterranean diet or, possibly, all of its components in combination are responsible for the association.
Practice Implications
Over the years this journal (and in particular, this author) has reviewed multiple studies on the Mediterranean diet. The diet is characterized by high consumption of fruit, vegetables, beans, and cereals, olive oil as the primary fat source, moderate consumption of fish, low to moderate intake of dairy products and wine (accompanying meals), and low intake of red meat and poultry. Increased adherence to this diet has been linked with lower inflammation, better cognitive function, reduced risk of Parkinson disease and Alzheimer disease, and mortality from cardiovascular disease and cancer.1-5
Three earlier studies have reported higher adherence to the Mediterranean diet is associated with larger brain volumes and cortical thickness as measured by MRI.6-8
The largest of these 3 studies (Gu 2015) reported that in Americans (n=468, average age 80.1 years) closer adherence was associated with greater brain volume. Those data suggested that higher fish and lower meat consumption were the primary contributors to these effects. These earlier studies only measured brain volume as a single point in time. This current study is of interest because it examines the effect of diet adherence over time, a difference that we might translate into a simple clinical implication: “The way you choose to eat now will affect how much your brain shrinks in the next few years.”
The results reported in this current study differ in some significant ways from earlier reports. Fish and meat consumption was not directly associated with brain volume, suggesting that the benefits of the Mediterranean diet cannot be narrowed down to these 2 attributes alone. We are left to choose between terms like holistic or synergistic to describe how the combined effects of the multiple dietary components, which make up this diet, interact together to provide benefit.
This current study is of interest because it examines the effect of diet adherence over time.
Measuring changes in brain volume and trying to determine associations is a complex process, and while the authors of this study attempted to control for a long list of possible confounders and other variables, we must look at these outcomes with reservation, even if the results are consistent with prior studies. Still, when we look at these findings in context with the positive results from other studies that suggest benefit from adherence to the Mediterranean diet, it appears easily conceivable that “preventing brain shrinkage” is just one more benefit this diet offers to those who follow it.
Admittedly the sheer simplicity of the Mediterranean diet can be a challenge. Many patients want more stringent guidelines, with lists of prohibited foods and more complex rules. They doubt that a relatively liberal diet that includes meat, gluten, wine, fruit, or any of a number of other items can be healthy. The propensity for some people to turn dietary suggestions into cult-like belief systems probably speaks more to deep psychological needs than to well-proven nutritional science. If you doubt this, search for diet books online and calculate what percentage of the titles give specific names to the diet, and what percentage of those names belong to the book’s author.
Food cults, and readers of this journal can no doubt name quite a few, have taken on an outsized role in modern culture. Dr. Kima Cargill in her new book writes:9
Food cults arguably replace what religion once did by prescribing organizing food rules and rituals. Like religion they provide meaning in confusing situations, giving us meaning and comfort. In urban secular cultures and locations such as the United States, food cults are more appealing than ever, both because they function as new religions and because of the unprecedented cultural premium placed on health, longevity and the body.
The challenge with promoting the Mediterranean diet is that it is almost too vague, too general, lacking the orthodoxy many people seem to crave.
Editor's note: Click for the free full text of the study reviewed here.
