A Mediterranean diet has been tied to better cognitive function, a lower rate of cognitive decline and a reduced risk of Alzheimer’s disease.
This eating pattern, plentiful in fruits and vegetables, whole grains, nuts and olive oil, has also been associated with lower rates of age-related brain atrophy, brain damage which can lead to cognitive impairment and dementia.
So far, though, there’s sparse data from randomized controlled trials on whether following a Mediterranean diet can preserve brain volume.
New research from Israel has shown that eating a Mediterranean diet slowed the age-related loss of brain tissue. What’s more, a new take on the diet, a “green” Mediterranean diet, had even greater brain-health benefits.
The latest study
The 18-month DIRECT PLUS trial, published Jan. 10 in the American Journal of Clinical Nutrition, investigated the effect of a high-polyphenol Mediterranean diet (a “green” Mediterranean diet) on age-related brain atrophy.
Polyphenols are naturally occurring compounds found in a wide range of plant foods. DIRECT PLUS stands for Dietary Intervention Randomized Controlled Trial – Polyphenols Unprocessed.
The researchers assigned 284 adults with abdominal obesity, average age 51, to one of three diet groups: 1) healthy diet guidelines, 2) a Mediterranean diet or, 3) a higher-polyphenol green Mediterranean diet.
Both Mediterranean diets were calorie-restricted and included 28 g of walnuts (e.g., 14 walnut halves), nuts high in polyphenols.
To boost polyphenols, the green Mediterranean diet included four to five cups of green tea daily and a green shake containing Mankai, a branded strain of an aquatic plant called duckweed (or water lentils). Those in the green Mediterranean diet group also further reduced their intake of processed and red meat.
All participants received free gym memberships and a program of aerobic and resistance exercise.
Participants underwent brain MRI (magnetic-resonance-imaging) scans before and after the trial. Specific areas of the brain were measured as indicators of brain atrophy and predictors of future dementia risk.
Over 18 months, participants in both Mediterranean diet groups had a significantly lower decline in brain atrophy compared to the healthy diet guideline group. The greatest decline in brain tissue loss, however, was observed among those consuming the green Mediterranean diet, especially in people over age 50.
The green Mediterranean diet components – green tea, Mankai and walnuts – were each associated with reduced brain atrophy, as was eating less red and processed meat.
Participants in both Mediterranean diet groups also had improvements in insulin sensitivity, which was also tied to less brain volume loss.
The study didn’t show a significant effect of either Mediterranean diet on cognition, perhaps because the study wasn’t long enough and/or it involved relatively young and healthy people.
All diet groups participated in physical exercise, which may have contributed to the slowdown of brain atrophy.
The strengths of this study include participants high adherence to their diets and that, to date, it’s the longest and largest brain MRI study investigating the effect diet on brain atrophy.
How polyphenols protect the brain
The beneficial effect of the Mediterranean diet on brain aging is thought to be due, at least in part, to its abundance of polyphenols, phytochemicals which have antioxidant and anti-inflammatory properties.
Polyphenols can cross the blood-brain barrier and have been shown to reduce nerve cell inflammation and stimulate an increase in brain cells.
Eating a Mediterranean diet rich in fish, vegetables and olive oil is also thought to protect the brain from a buildup of proteins that form plaques and destroy brain cells.
‘Greening’ your Mediterranean diet
Following a Mediterranean eating pattern means including vegetables, fruit, whole grains, pulses, nuts and olive oil in your daily diet.
Limit red meat to three meals a week. The green Mediterranean diet limits meat even further, getting more protein from beans, lentils and nuts. Flavour meals with polyphenol-rich herbs and spices.
Build on these staples by adding more polyphenol-rich foods to your daily diet, including 28 g of walnuts. Drink three or four cups of green tea each day (white and oolong tea also have polyphenols).
Drinking a Mankai green shake may be more challenging, though, at least for Canadians. In the U.S., frozen cubes of Mankai duckweed are sold online through Amazon and WW (Weight Watchers). Mankai duckweed powder is also available online.
Add other polyphenol-rich foods to your diet, too, such as berries, apples, kale, broccoli, spinach, cocoa, tofu, edamame, flaxseed and pecans.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD
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