The Mediterranean diet has been linked to better cognitive function, a lower rate of cognitive decline and a reduced risk of Alzheimer’s disease.
This eating pattern, which is abundant in fruits, vegetables, whole grains, nuts and olive oil, has been linked to lower rates of age-related brain atrophy and brain damage that can lead to cognitive impairment and dementia.
So far, though, there is scattered data from randomized controlled trials about whether a Mediterranean diet can preserve brain volume.
New research from Israel shows that eating a Mediterranean diet slows age-related brain tissue loss. Moreover, a new diet, the “green” Mediterranean diet, had even greater benefits for brain health.
The 18-month DIRECT PLUS trial, published January 10 in the American Journal of Clinical Nutrition, investigated the effect of a Mediterranean diet high in polyphenols (a “green” Mediterranean diet) on age-related brain atrophy.
Polyphenols are natural compounds found in a wide variety of plant foods. DIRECT PLUS means a randomized controlled trial of a dietary intervention – untreated polyphenols.
The researchers assigned 284 obese adults, average age 51, to one of three diet groups: 1) healthy diet guidelines, 2) a Mediterranean diet, and 3) a green Mediterranean diet high in polyphenols.
Both Mediterranean diets were calorie restricted and included 28 grams of walnuts (for example, 14 walnut halves), nuts that are high in polyphenols.
For a polyphenol boost, the Mediterranean diet included four to five cups of green tea per day and a green shake containing mankai, a branded strain of an aquatic plant called duckweed (or water lentil). Those in the Mediterranean diet group also reduced their intake of processed and red meat.
All participants received a free gym membership and aerobic and resistance training programme.
Participants underwent brain magnetic resonance imaging (MRI) before and after the experiment. Certain areas of the brain were measured as indicators of brain atrophy and predictors of future dementia risk.
Over the course of 18 months, participants in both Mediterranean diet groups had a significant reduction in brain atrophy compared to the healthy diet guideline group. However, the greatest reduction in brain tissue loss was observed among those consuming a green Mediterranean diet, especially in people over 50 years of age.
Components of the Mediterranean diet — green tea, mankai and walnuts — were associated with lower brain atrophy, as well as eating less red and processed meat.
Participants in both Mediterranean diet groups also showed improvements in insulin sensitivity, which was also linked to less loss of brain volume.
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Limitations and strengths
The study did not show a significant effect of the Mediterranean diet on cognition, possibly because the study was not long enough and/or it included relatively healthy people.
All of the diet groups engaged in physical exercise, which may have slowed brain atrophy.
The strengths of this study include participants’ strict adherence to their diets, which is to date the longest-running and largest MRI of the brain study looking at the effect of diet on brain atrophy.
How do polyphenols protect the brain?
The beneficial effect of the Mediterranean diet on brain aging is believed to be due, at least in part, to the abundance of polyphenols, phytochemicals that have antioxidant and anti-inflammatory properties.
Polyphenols can cross the blood-brain barrier and have been shown to reduce neuronal inflammation and stimulate an increase in brain cells.
It is also believed that a Mediterranean diet rich in fish, vegetables and olive oil protects the brain from the buildup of proteins that form plaques and destroy brain cells.
Greening your Mediterranean diet
Following a Mediterranean eating pattern means including vegetables, fruits, whole grains, legumes, nuts and olive oil in your daily diet.
Limit red meat to three meals a week. The Mediterranean diet limits meat more, and gets more protein from beans, lentils, and nuts. Flavor meals with herbs and spices rich in polyphenols.
Rely on these essential nutrients by adding more polyphenol-rich foods to your daily diet, including 28 grams of walnuts. Drink three or four cups of green tea every day (white tea and oolong tea also contain polyphenols).
Drinking the green mancay drink may be more difficult, at least for Canadians. In the United States, frozen cubes of Mankai duckweed are sold online through Amazon and WW (Weight Watchers). Mankai duckweed powder is also available online.
Add other foods rich in polyphenols to your diet as well, such as berries, apples, kale, broccoli, spinach, cocoa, tofu, edamame, flaxseeds, and groundnuts.
Leslie Beck, a Toronto-based private dietitian, is Medcan’s director of food and nutrition. Follow her on Twitter Tweet embed
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