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Relation
Luciano M, Corley J, Cox SR, et al. Mediterranean diet and brain structural change from 73 to 76 years of age in a Scottish cohort.neurology. 2017;88(5):449-455.
Participant
Participants in this study were from the 1936 Lothian Cohort, a group of 1,091 participants born in Edinburgh, Scotland, in 1936. You were 70 years old at the start of your studies. Dietary data were collected via mailed questionnaires. Three and then 6 years later, able and willing participants underwent structural magnetic resonance imaging (MRI) of the brain.
Target parameters
Two longitudinal brain volumes (total and gray matter; n = 401 and 398, respectively) plus a longitudinal measure of cortical thickness (n = 323) were measured. Adherence to the Mediterranean diet was calculated using data collected from a food frequency questionnaire at age 70 years, 3 years before baseline imaging data collection.
Key insights
Lower adherence to the Mediterranean diet was associated with a greater 3-year reduction in total brain volume (explaining 0.5% of the variance,P<0.05). Lower adherence to the Mediterranean diet in an older Scottish cohort is a predictor of total brain atrophy over 3 years. Consumption of fish and meat does not drive this change, suggesting that other components of the Mediterranean diet, or perhaps all of its components in combination, are responsible for the association.
Practice implications
Over the years, this journal (and this author in particular) has reviewed several studies on the Mediterranean diet. The diet is characterized by high consumption of fruits, vegetables, beans and grains, olive oil as the primary source of fat, moderate consumption of fish, low to moderate consumption of dairy products and wine (with meals), and low consumption of red meat and poultry. Increased adherence to this diet has been linked to lower inflammation, better cognitive function, reduced risk of Parkinson's and Alzheimer's disease, and mortality from cardiovascular disease and cancer.1-5
Three previous studies have reported that higher adherence to the Mediterranean diet is associated with greater brain volume and cortical thickness as measured by MRI.6-8
The largest of these 3 studies (Gu 2015) reported that closer adherence was associated with larger brain volume in Americans (n = 468, mean age 80.1 years). These data suggested that higher fish and lower meat consumption were the main causes of these effects. These previous studies only measured brain volume at a single time point. This current study is of interest because it examines the effects of diet adherence over time, a difference that we could translate into a simple clinical implication: “The way you eat now will affect how much your brain shrinks in the next few years.”
The results reported in this current study differ from previous reports in several important ways. Fish and meat consumption were not directly linked to brain volume, suggesting that the benefits of the Mediterranean diet cannot be limited to these two characteristics alone. We are left to choose between terms such as holistic or synergistic to describe how the combined effects of the multiple nutritional components that make up this diet work together to produce benefit.
This current study is of interest because it examines the effects of diet adherence over time.
Measuring changes in brain volume and attempting 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 view these results with caution, even if the results are consistent with previous studies. However, if we consider these results in the context of the positive results of other studies suggesting a benefit from following the Mediterranean diet, it seems easy to imagine that “preventing brain shrinkage” is just another benefit that this diet offers to those who follow it.
Admittedly, the sheer simplicity of the Mediterranean diet can be challenging. Many patients want stricter guidelines with lists of banned foods and more complex rules. They doubt that a relatively liberal diet that includes meat, gluten, wine, fruit or a range of other foods can be healthy. Some people's tendency 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 diet's titles give specific names and what percentage of those names belong to the book's author.
Food cults, and readers of this magazine can undoubtedly name a few, have assumed a predominant role in modern culture. Dr. Kima Cargill writes in her new book:9
Food cults arguably replace what religion once did by prescribing rules and rituals for organizing food. Like religion, they make sense of confusing situations, giving us meaning and comfort. In urban secular cultures and places like the United States, food cults are more attractive than ever, both because they function as new religions and because of the unprecedented cultural importance placed on health, longevity, and the body.
The challenge with promoting the Mediterranean diet is that it is almost too vague, too general, and lacks the orthodoxy that many people seem to crave.
Editor's note: Click for the free full text of the study reviewed here.