Numerous studies have shown brain health benefits of the Mediterranean diet, which consists of high amounts of vegetables, fruits, whole grains, fish, poultry, legumes, nuts, and monounsaturated fats (e.g., olive oil) [1; 2; 3]. How is the Green Mediterranean diet different? The Green Mediterranean diet is a Mediterranean diet with higher levels of polyphenols with antioxidant and anti-inflammatory properties, while completely avoiding red/processed meat. In a new clinical study, people assigned to the Green Mediterranean diet had less decline in the volume of the hippocampus, a brain region important for memory functions, compared to people assigned to a control group .
These findings come from a randomized controlled trial that enrolled 284 participants with obesity or dyslipidemia (abnormal blood levels of cholesterol and triglycerides), who were randomly assigned to one of three groups . A control group received nutritional counseling promoting a healthy diet. The Mediterranean diet group consumed a low-calorie traditional Mediterranean diet, rich in vegetables, with poultry and fish partly replacing beef and lamb, and 28 grams per day of walnuts, which contain high levels of polyphenols. The Green Mediterranean diet group followed the same instructions as the Mediterranean diet group, but in addition, consumed 3-4 cups per day of green tea and a green shake for dinner, consisting of 100 grams of Mankai (Wolffia globosa), an aquatic plant rich in polyphenols . The Green Mediterranean diet group was also instructed to avoid processed and red meat completely and consume more plant-based food. All participants of the study received free gym memberships and physical activity guidance. This dietary intervention continued for 18 months. Of the 284 participants, 224 completed the study including whole-brain imaging with magnetic resonance imaging (MRI).
After 18 months, there was an overall decline in the volume of the hippocampus due to the normal changes that occur with aging, and this decline was more pronounced in participants over 50, consistent with previous findings showing that atrophy of the hippocampus accelerates at the age of 55 . However, in participants over the age of 50, there was less decline in the volume of the hippocampus in people eating the Mediterranean diet compared to those in the control group, with the best outcomes seen in people consuming the Green Mediterranean diet. Many metrics were associated with slower decline in the volume of the hippocampus. For people over the age of 50, weight loss, better insulin sensitivity (measured by HOMA-IR), and lower triglyceride levels were associated with slower decline in hippocampus size. For all age groups, greater intake of Mankai, green tea, and walnuts, and reduced intake of red and processed meat were associated with slower decline in hippocampus size. This finding was partly confirmed by a urine analysis, where participants with high urine levels of specific polyphenols, reflecting high dietary intake of polyphenols, had slower decline in hippocampus size.
Interestingly, neither the Mediterranean diet nor the Green Mediterranean diet were associated with benefits in cognitive functions in this study. This lack of cognitive effect may be explained by the relatively young age (average, 51 years old) and good baseline cognitive health of the study participants, the small size of the study, and the short intervention time. A future larger study with a longer intervention in an older population may be able to explore potential cognitive effects with the Green Mediterranean diet.
Why might the Green Mediterranean diet be beneficial for brain health? In preclinical studies, plant-based polyphenols exert antioxidant and anti-inflammatory effects, increase the numbers of neurons in the hippocampus, and decrease the levels of toxic proteins associated with Alzheimer’s disease [7; 8; 9].
There is now ample evidence that the Mediterranean diet is beneficial for brain health. For a brain-healthy diet, incorporate more vegetables, fruits, whole grains, legumes, and nuts, while limiting processed or red meat. To emulate the Green Mediterranean diet, Mankai may be difficult to find, particularly in the same form used in clinical trials. But it is not hard to increase your dietary intake of polyphenols—for example, add green tea, coffee, walnuts, or cocoa.
Yuko Hara, PhD, is Director of Aging and Alzheimer's Prevention at the Alzheimer's Drug Discovery Foundation. Dr. Hara was previously an Assistant Professor in Neuroscience at the Icahn School of Medicine at Mount Sinai, where she remains an adjunct faculty member. Her research focused on brain aging, specifically how estrogens and reproductive aging influence the aging brain's synapses and mitochondria. She earned a doctorate in neurology and neuroscience at Weill Graduate School of Medical Sciences of Cornell University and a bachelor's degree in biology from Cornell University, with additional study at Keio University in Japan. Dr. Hara has authored numerous peer-reviewed publications, including articles in PNAS and Journal of Neuroscience.
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