Age-related brain atrophy (shrinkage) may be slowed by following a “green” Mediterranean-style diet that’s high in polyphenols from green plants, according to a new study published in The American Journal of Clinical Nutrition.
The Mediterranean diet, which is modeled after eating patterns from several countries that border the Mediterranean Sea, involves eating plenty of vegetables and fruits, whole grains, olive oil, beans and other legumes, and lean sources of protein — and limiting refined carbohydrates, sugar, red and processed meat, and animal fats. Since it’s a fairly flexible eating pattern that doesn’t involve strictly tracking calories or nutrients, the Mediterranean diet is often ranked as one of the best diets to follow — including for people with diabetes. This flexibility means that there are several variations of the Mediterranean diet, some of which focus on getting lots of plant polyphenols — a category of beneficial nutrients that have an antioxidant effect in the body, protecting cells from damage. This so-called “green” Mediterranean diet has been shown in previous studies to have unique health benefits, including improving insulin sensitivity and reducing liver fat — two benefits that are especially relevant to people with type 2 diabetes.
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The effect of the “green” Mediterranean diet on brain health
For the latest study, researchers were interested in how following a “green” Mediterranean diet might affect brain atrophy as people get older. Some amount of brain shrinkage is typical with increasing age, and some diseases are known to speed up this process — potentially leading to cognitive impairment and dementia. There isn’t much existing evidence, though, to support any dietary interventions known to slow age-related brain atrophy.
The study’s participants were 284 adults ages 31 to 82, with an average age of 51. The average body-mass index (BMI, a measure of body weight that takes height into account) of participants was 31 — which falls in the category of obesity — and 88% of participants were men. Participants had their brain volume measured using magnetic resonance imaging (MRI) at the start of the study, as well as at the end of the study after 18 months. During the study period, participants were randomly assigned to one of three groups — a general healthy diet group, a Mediterranean diet group, and a “green” Mediterranean diet group. The “green” Mediterranean diet group consumed more polyphenols — including by drinking three to four cups of green tea each day, and drinking a shake made with frozen cubes of the Mankai plant — and less red or processed meat than the regular Mediterranean diet group. Both Mediterranean diet groups ate 28 grams each day of walnuts, which are a good source of polyphenols. All study participants received free gym memberships and guidance on physical activity.
Among the 224 participants who completed the study, it was clear that older age was linked to greater brain atrophy — participants ages 50 and older saw an average decrease in one measure of brain volume (hippocampal occupancy) of 1.0%, while those younger than 50 saw a decrease of only 0.06%. For another measure (lateral ventricle volume), people ages 50 and older saw an average decrease of 3.2%, while it went down by only 1.3% in younger participants. But among participants ages 50 and older, both of these brain volume decreases were smaller in the two Mediterranean diet groups than in the standard healthy diet group — and the smallest decreases were seen in the “green” Mediterranean diet group, with a 0.8% drop in hippocampal occupancy (compared with 1.3% in the healthy diet group) and a 2.3% drop in lateral ventricle volume (compared with 4.3% in the healthy diet group).
Similar slowing of brain atrophy was seen in younger participants who followed the “green” Mediterranean diet, although with much smaller decreases seen in all groups. The researchers also found that the single most important clinical measurement that predicted brain shrinkage was insulin sensitivity — which was greater in the “green” Mediterranean diet group. While this link alone doesn’t prove causation, it’s possible that the effect of different diets on insulin sensitivity was responsible for at least some of the variation in brain atrophy seen in the study. Elevated urine levels of two polyphenols found in Mankai (urolithin and tyrosol) were also inked to a lower risk for brain atrophy.
“A Green [Mediterranean], high-polyphenol diet, rich in Mankai, green tea and walnuts and low in red/processed meat is potentially neuroprotective for age-related brain atrophy,” the researchers concluded. These results offer guidance to anyone wondering what foods to eat most often when following a Mediterranean-style diet, if reducing the risk for cognitive decline is a top priority.
Want to learn more about the Mediterranean diet? Read “Five Reasons to Try the Mediterranean Diet” and “Eating Patterns and Type 1 Diabetes: Mediterranean Diet,” then try five of our favorite diabetes-friendly Mediterranean recipes.
Want to learn more about maintaining cognitive health with diabetes? Read “Nine Tips to Keep Your Memory With Diabetes,” “Keeping Your Brain Strong With Diabetes” and “Memory Fitness: How to Get It, How to Keep It.”