How (and why) to ‘green’ your Mediterranean diet

A Mediterranean diet has been linked to better cognitive function, a lower rate of cognitive decline, and a lower risk of Alzheimer’s disease.

This eating pattern, rich in fruits and vegetables, whole grains, nuts, and olive oil, has also been associated with lower rates of age-related brain atrophy, brain damage that can lead to cognitive decline and dementia.

However, so far, there is scant data from randomized controlled trials on whether following a Mediterranean diet can preserve brain volume.

Up to now.

New research from Israel has shown that eating a Mediterranean diet slows age-related brain tissue loss. In addition, a new version of the diet, a “green” Mediterranean diet, had even greater benefits for brain health.

the last study

The 18-month DIRECT PLUS trial, published January 10 in the American Journal of Clinical Nutrition, investigated the effect of a polyphenol-rich Mediterranean diet (a “green” Mediterranean diet) on age-related brain atrophy.

Polyphenols are natural compounds found in a wide range of plant foods. DIRECT PLUS stands for Randomized Controlled Trial of Dietary Intervention: Raw Polyphenols.

The researchers assigned 284 adults with abdominal obesity, average age 51, to one of three diet groups: 1) healthy dietary guidelines, 2) a Mediterranean diet, or 3) a Mediterranean diet rich in green polyphenols.

Both Mediterranean diets were calorically restricted and included 28 g of walnuts (eg, 14 walnut halves), polyphenol-rich nuts.

To boost polyphenols, the Mediterranean Green Diet included four to five cups of green tea daily and a green smoothie containing Mankai, a brand name strain of an aquatic plant called duckweed (or duckweed). Those in the green Mediterranean diet group also further reduced their consumption of red and processed meat.

All participants received free gym memberships and an aerobic and resistance exercise program.

The participants underwent brain MRIs (magnetic resonance imaging) 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 smaller decrease in brain atrophy compared to the healthy diet guide group. However, the greatest decrease in brain tissue loss was seen among those who ate the green Mediterranean diet, especially those over 50 years of age.

The green components of the Mediterranean diet (green tea, Mankai, and walnuts) were 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 linked to less brain volume loss.

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limitations, strengths

The study did not show a significant effect of the Mediterranean diet on cognition, perhaps because the study was not long enough and/or involved relatively young and healthy people.

All diet groups participated in physical exercise, which may have contributed to the slowing of brain atrophy.

Strengths of this study include the high adherence of participants to their diets and that, to date, it is the largest and longest brain MRI study investigating the effect of 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 that have antioxidant and anti-inflammatory properties.

Polyphenols can cross the blood-brain barrier and have been shown to reduce nerve cell inflammation and stimulate brain cell growth.

Eating a Mediterranean diet rich in fish, vegetables, and olive oil is also believed to protect 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 green Mediterranean diet further limits meat, getting more protein from beans, lentils and nuts. Season meals with polyphenol-rich herbs and spices.

Take advantage of these staples by adding more polyphenol-rich foods to your daily diet, including 1 ounce of walnuts. Drink three to four cups of green tea a day (white and oolong teas also have polyphenols).

However, drinking a Mankai green smoothie can be more challenging, at least for Canadians. In the US, Frozen Mankai Duckweed Cubes are sold online through Amazon and WW (Weight Watchers). Mankai duckweed powder is also available online.

Also add other polyphenol-rich foods to your diet, such as berries, apples, kale, broccoli, spinach, cocoa, tofu, edamame, flaxseed, and walnuts.

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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