Polyphenols, as found in walnuts, can cross the blood-brain barrier and reduce inflammation.
Over the past decade, the Mediterranean diet has consistently been tied to improved brain health.
Adhering to the diet is associated with better memory, larger brain volume (less brain atrophy), slower cognitive decline and protection against dementia.
A modified version of the Mediterranean diet – the green-Mediterranean diet – has also been linked to a slower rate of brain aging with evidence suggesting it may have a slight edge over the traditional Mediterranean diet.
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Now, new research supports the idea that the green-Mediterranean diet (green-MED diet) can amplify the brain benefits of the original dietary pattern.
According to the findings, the green-MED diet can lower levels of key blood proteins involved in accelerated brain aging.
Here’s what to know about the study, plus specific green-MED diet foods to include in your regular diet.
What’s in the green-MED diet?
Like the traditional Mediterranean diet, the green-MED diet is plentiful in vegetables, fruits, nuts, pulses, whole grains and olive oil.
Where the two diets differ, though, is that the green-MED diet doesn’t include any processed and red meat (the Mediterranean diet includes a little). It focuses on plant protein with small amounts of fish and poultry.
The green-MED diet is also higher in polyphenols, phytochemicals with antioxidant and anti-inflammatory properties.
To increase polyphenols, the green-MED diet includes a daily intake of three to four cups of green tea and a green shake containing Mankai, a branded strain of an aquatic plant called duckweed (Wolffia globosa).
About the latest research
The new findings, published Sept. 1 in the journal Clinical Nutrition, analyzed data from the DIRECT PLUS trial, one of the longest-running trials on diet and brain health.
The researchers set out to learn whether levels of circulating proteins in the bloodstream were different between people with distinct rates of brain aging, and whether these changes were influenced by diet.
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For the 18-month trial, nearly 300 participants with abdominal obesity and an average age of 51 were assigned to one of three diets: standard healthy eating guidelines, a traditional Mediterranean diet or a green-MED diet. Both Mediterranean diets were calorie-reduced and included 28 g of polyphenol-rich walnuts.
The researchers measured participants’ serum levels of 87 proteins at the start of the study and at 18 months. Serum is the liquid component of blood that remains after blood cells and clotting factors are removed.
Whole-brain MRI scans were performed before and after the study to assess changes in brain health.
Brain MRIs were used to calculate each participant’s “brain age gap,” defined as the difference between a person’s MRI-predicted brain age and their actual chronological age.
A higher, or positive, brain age gap indicates an older brain age than expected (accelerated brain aging), whereas a negative brain age gap reflects a brain age lower than chronological age (reduced brain aging).
Lifestyle factors such as smoking, heavy alcohol use, poor diet and lack of physical exercise can accelerate brain aging. So can inflammation, hypertension, high cholesterol, diabetes and the accumulation of beta-amyloid plaques and tau tangles in the brain, proteins that disrupt brain cell function.
Green-MED diet targets damaging proteins
A higher level of two specific serum proteins, Galectin-9 and Decorin, were significantly associated with accelerated brain aging.
In the brain, Galectin-9 has been implicated with initiating inflammation. Elevated levels of the protein have also been associated with mild cognitive impairment and progression toward Alzheimer’s disease.
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Higher levels of Decorin are associated with early beta-amyloid plaque formation, a hallmark sign of Alzheimer’s disease.
Over 18 months, only participants in the green-MED diet group had a significant reduction in Galectin-9.
Decorin increased in all three diet groups, but those adhering to the green-MED diet had a slower rise in the harmful protein.
The protective effect of the green-MED diet is thought to be owing to its high polyphenol content – especially from walnuts, green tea, Mankai green shakes and extra virgin olive oil.
Polyphenols can cross the blood-brain barrier and reduce inflammation. They can also increase blood flow to the brain and stimulate the formation of new brain cells. They’ve also been shown to reduce beta-amyloid accumulation.
Strengths, limitations
These new findings align with earlier results from the DIRECT PLUS trial showing the green-MED diet slowed age-related brain atrophy by about 50 per cent within 18 months.
Still, the study is not without limitations.
It enrolled primarily men so whether the findings are relevant for women needs to be confirmed. The study also lacks information about participants’ cognitive status.
Simple ways to adopt a polyphenol-rich Mediterranean diet
Include vegetables, fruit, whole grains and pulses (beans, chickpeas and lentils) in your daily diet. Make extra virgin olive oil your principal cooking oil.
Add 28 g (about one-quarter cup) of walnuts to your daily diet – as a snack, tossed into salads, sprinkled on oatmeal and yogurt or blended into smoothies.
Sip on unsweetened green tea each day, hot or iced. Aim for three to four cups.
Include polyphenol-rich produce in your diet such as arugula, kale, broccoli, spinach, parsley, artichokes, berries and apples.
Mankai duckweed powder is not available in North America, but duckweed powder is available online from Etsy.com; Amazon.com carries water lentil powder, a member of the duckweed family.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on X @LeslieBeckRD
