The Mediterranean diet has plenty of benefits, whether you’re concerned about your blood sugar or just want to extend your life. And it’s no surprise that every time we turn around, yet another study comes out to remind us just how great the Mediterranean diet can be.

We already know that people who follow a Mediterranean diet eating pattern tend to have healthier hearts, brains and weight. But scientists continue to dig into the “why” and “how” of these benefits. How does the Mediterranean diet affect the inner workings of our bodies to create these benefits? This new study published in the November 2024 issue of The American Journal of Clinical Nutrition sheds some light. Here’s what they found. 

How Was This Study Conducted?

Age-related brain atrophy—or shrinking—is a normal aging process. And people with type 2 diabetes tend to have greater atrophy than people without diabetes. That atrophy matters because bigger brains tend to be healthier, and smaller brains are related to brain disorders, including cognitive decline, dementia and Alzheimer’s disease.

These study authors previously did another study that suggested that both a traditional Mediterranean diet and a green Mediterranean diet significantly reduced age-related brain shrinking by about 50% within 18 months. They now wanted to hone in on the mechanisms behind these eating patterns that protect the brain. 

For this study, called the DIRECT PLUS brain-MRI trial, researchers hypothesized that improved glycemic control—stable blood sugar—is a contributing factor to the brain-protecting effects of diet on brain aging and that this may play a key role in promoting a younger brain age. 

To test their hypothesis, they recruited 284 individuals to participate in this study. The average age was 51 and 88% of them were male. All the participants had abdominal obesity—a waist circumference of greater than 102 cm for men and 88 cm for women—or they had dyslipidemia—high triglycerides (>150 mg/dL) and low HDL cholesterol (≤40 mg/dL for men and ≤50 mg/dL for women).

Participants were then randomly assigned to one of three intervention groups: a typical healthy eating pattern based on dietary guidelines, a traditional calorie-restricted Mediterranean diet that was low in simple carbohydrates or the green Mediterranean diet. 

Each group received specific instructions regarding diet and physical activity. The healthy eating group received basic health-promoting guidelines for maintaining a healthy diet—something like the 2020-2025 Dietary Guidelines for Americans. 

Participants in the traditional Mediterranean diet group received guidelines for maintaining a calorie-restricted traditional Mediterranean diet that was low in simple carbs and high in vegetables. Lamb and beef were replaced with poultry and fish. 

The green-Mediterranean diet went a step further and was lower in processed and red meat than the traditional Mediterranean diet, and even richer in plants and polyphenols. (Polyphenols are plant compounds with anti-inflammatory properties—dark leafy greens, like kale, and berries tend to be rich in them.) This was accomplished by eating more plants and including 3-4 cups of green tea a day and 500 mL of a Mankai-based green shake at dinner. Mankai, also known as duckweed or watermeal, is a tiny aquatic plant rich in protein, fiber, antioxidants, iron, B12, choline and omega-3s. The protein in Mankai is complete, making it one of the few plant-based sources of complete protein.

Both Mediterranean diet groups also consumed 28 grams of walnuts per day, which are known for their brain-boosting abilities. And both groups were equally calorie-restricted—1500-1800 calories per day for men and 1200-1400 calories per day for women.

All three groups received a couple of additional perks—a gym membership, physical activity guidelines and occasional 90-minute nutritional and physical activity sessions in the workplace. 

While 284 individuals entered the study, 224 made it all 18 months. Each participant took certain tests at the beginning of the study to establish a baseline, and researchers repeated those tests after 18 months, which is how long the study lasted. These tests included basic measurements, like height, weight, blood pressure and heart rate, plus blood samples and a brain MRI.

What Did the Study Find?

Researchers ran numerous statistical analyses and uncovered several interesting findings:

• Greater glycemic control seems to have an independent beneficial effect on MRI-assessed brain age. In other words, those with more stable blood sugar over the 18 months had younger, larger brains, irrespective of age and other factors.
• Greater consumption of polyphenols by drinking green tea and Mankai resulted in younger brains.
• Those on either Mediterranean diet had more brain growth after 18 months compared to those on the general healthy eating plan, but those on the green Mediterranean diet had the greatest brain growth—due to the added polyphenols, researchers surmise.
• Those who went from pre-diabetes at the beginning of the study to normal status at the end showed improvements in brain age.
• Participants who lowered their inflammatory markers during the study period also showed an increase in brain size.

Essentially, the Mediterranean diet participants had greater positive changes in brain age and size compared to the healthy eating group. But the green Mediterranean diet group had the greatest changes. 

The researchers felt there were at least two main pathways for these improvements. First, the Mediterranean diets tended to produce better blood sugar control and this seemed to have protective benefits on the brain—thus, supporting their hypothesis. 

They also found that the green-Mediterranean diet had the greatest benefits out of the three diets. They feel this is due to the increase in polyphenols, primarily from green tea and Mankai. Specifically, they found that drinking more than three Mankai shakes a week was associated with greater brain mass compared to those who drank fewer than three shakes a week. Similarly, those who drank at least two cups of green tea a day tended to exhibit greater increases in brain mass. 

How Does This Apply to Real Life?

So what does this mean for those of us who want to protect our brains and slow the brain aging and atrophy process? In a nutshell: try following a Mediterranean diet and sipping on green tea each day. And if you’re able, include Mankai shakes several times a week—that could be an especially good idea if you’re already on the hunt for more plant-based protein sources.

The Mediterranean diet includes lots of fruits, vegetables, whole grains, nuts, seeds, healthy fats—like olive oil—and lean proteins—like fish and poultry. Processed meats, red meat, dairy and sweets are kept to a minimum. 

The participants in this study also engaged in physical activity. According to the study’s supplemental material, they were advised to start with 20 minutes of cardio and gradually work up to 45-60 minutes plus resistance training 3-4 times per week. The resistance training included basic exercises, including leg extensions, leg curls, squats, lateral pull-downs, push-ups, shoulder presses, elbow flexions, triceps extensions and bent leg sit-ups.

We also know that stress can affect brain health, as can loneliness, so find ways to manage your stressors and get social—preferably in person. Sleep can influence brain health, too—a lack of sleep may increase your risk of dementia.

The Bottom Line

This study found a connection between better blood sugar control and bigger brain size. Better blood sugar control was accomplished by following a Mediterranean diet. The green Mediterranean diet showed the greatest brain protection, blood sugar control and reduction in inflammatory markers, in part, due to its higher level of polyphenols. 

There are a couple of limitations to this study. Because 88% of the participants were male, it’s hard to say if these results benefit women as much. And with an average age of 51, we can’t say if these benefits apply to older individuals who may already be experiencing brain atrophy. 

Regardless, you’re never too old—or too young—to make changes, so start following a Mediterranean diet pattern today for a healthy brain. For added brain benefits, include green tea, Mankai, exercise, socialization, plenty of quality sleep and control your stressors. These changes will not only benefit your brain, but your heart, disease risk and overall health, as well.