Short answer: Preliminary. In one 18-month trial (DIRECT-PLUS), both Mediterranean diets slowed MRI markers of shrinkage around the hippocampus in people aged 50 and over, with the best results on the green version. It wasn’t shown to beat the standard Mediterranean diet, and cognition wasn’t measured. Green tea, walnuts and less red meat are easy to try.

The green-Mediterranean diet has early, preliminary evidence for brain aging. It comes from one 18-month trial that measured brain structure on MRI, not memory or thinking. The green version was not shown to be clearly better than the standard Mediterranean diet.

What the green-Mediterranean diet adds

It keeps the base of the Mediterranean diet: vegetables, legumes, whole grains, olive oil, nuts and fish, with little processed food. Then it makes four changes to raise polyphenol intake (polyphenols are plant compounds with antioxidant and anti-inflammatory effects):

  • Mankai shake: 100 g per day of Mankai (Wolffia globosa), a tiny aquatic plant, a type of duckweed, blended as a frozen green shake. Mankai is a high-protein strain developed by an Israeli company.
  • Green tea: 3–4 cups a day.
  • Walnuts: 28 grams a day. In the trial, the standard Mediterranean group got the same walnuts.
  • Almost no red or processed meat: Fish, poultry, legumes and plant protein, including Mankai, replace it.

In DIRECT-PLUS, the foods given to the green group added about 1,240 mg of polyphenols a day. The walnuts given to the standard Mediterranean group added about 440 mg. These are amounts added on top of the usual diet, not total intake.

How to try it, and who should be careful

  1. Start with a solid Mediterranean base. The green additions build on vegetables, legumes, whole grains, fish, olive oil and nuts; they don’t replace them.
  2. Drink green tea. The trial group drank 3–4 cups a day. Green tea contains caffeine: the usual upper intake for healthy adults is about 400 mg a day from all sources, and 200 mg a day in pregnancy. Caffeine-sensitive people may get insomnia, anxiety or stomach upset; decaf is an option.
  3. Eat a small handful of walnuts daily. The trial used 28 grams.
  4. Cut red and processed meat as far as you can sustain. The green group nearly eliminated it. A partial cut is likely still helpful.
  5. Try Mankai if you can find it. It is not widely sold in most Western countries; as of early 2026 it is available frozen or as a powder from specialty and online sellers. Other green powders such as moringa, chlorella or spirulina share some of its nutrients but haven’t been tested this way. They are sold as supplements, so ask a doctor or pharmacist before using them, especially if you take medication.
  6. Get polyphenols from many foods. Berries, dark chocolate, turmeric, rosemary, olive oil, red onions and colorful vegetables all count.
  7. Keep moving. All three trial groups got a free gym membership and exercise guidance.

Safety notes. If you take an anticoagulant such as warfarin, talk to your doctor before sharply increasing green tea or leafy greens, because vitamin K can interact with these drugs. People with kidney disease should be cautious with high-polyphenol diets, since some polyphenol breakdown products leave the body through the kidneys. Skip the walnuts if you have a nut allergy. For most healthy adults eating these foods, no clear safety concerns have been identified.

What the DIRECT-PLUS trial found

DIRECT-PLUS was an 18-month randomized trial at a workplace, the Nuclear Research Center Negev in Dimona, Israel, led by Iris Shai at Ben-Gurion University. It enrolled 294 adults with abdominal obesity or unhealthy blood fats. Most were men (88 percent), with an average age of about 51. People were assigned to one of three groups:

  • Healthy dietary guidelines: general healthy-eating advice.
  • Mediterranean: a calorie-restricted Mediterranean diet with 28 g of walnuts a day, more vegetables, fish and legumes, and less red meat.
  • Green-Mediterranean: the same diet, calorie target and walnuts, plus the Mankai shake and green tea, and red meat cut to near zero.

Brain MRI results

Kaplan 2022 reported the brain scans. Of 284 people in the MRI study, 224 finished with usable scans at the start and at 18 months. The researchers tracked two markers of brain shrinkage. One was hippocampal occupancy: the size of the hippocampus, a memory center, relative to the fluid space next to it. The other was enlargement of the fluid-filled ventricles.

Shrinkage was faster in people aged 50 and over, and the main diet effects were reported in that group. In them, both Mediterranean groups lost less hippocampal occupancy and had less ventricle enlargement than the guidelines group. The green group did best: hippocampal occupancy changed by -0.8% vs -1.3% with standard advice, and the ventricles grew 2.3% vs 4.3%. Similar patterns appeared in younger people. The abstract doesn’t report a clear difference between the green and standard Mediterranean groups.

What went with less shrinkage

The researchers then looked at which changes tracked with the MRI results. These are associations within the trial, not randomized comparisons.

  • Insulin sensitivity: Better insulin sensitivity was the factor most strongly linked to less brain shrinkage. (More on this in our page on blood sugar and the brain.)
  • Polyphenol markers: Higher urine levels of urolithin A (from walnuts) and tyrosol were linked to less hippocampal decline.
  • Foods: Eating more Mankai, green tea and walnuts, and less red and processed meat, were each linked to less hippocampal decline.

In a later post hoc analysis (Pachter 2024), the team used hippocampal occupancy relative to what is expected for a person’s age as a stand-in for “brain age”. Slower brain aging on this measure went with improvements in HbA1c (a long-term blood sugar measure), insulin resistance, fasting glucose and C-reactive protein. It also went with eating more Mankai and green tea, beyond the effect of weight loss. It didn’t report a difference in years of brain age between groups.

Other results from the same trial

Compared with the standard Mediterranean group, the green group had:

  • a greater fall in C-reactive protein, a blood marker of inflammation, at 6 months (Tsaban 2021);
  • a greater drop in waist size at 6 months (-8.6 cm vs -6.8 cm), despite similar weight loss;
  • about twice as much loss of liver fat over 18 months (Yaskolka Meir 2021).

At 6 months the green group also improved more than the guidelines group in LDL cholesterol, diastolic blood pressure and insulin resistance. A separate analysis found larger changes in gut bacteria in the green group, which statistically appeared to explain part of its effect on weight and heart-health markers (Rinott 2022).

Why more polyphenols might help

The idea behind the diet is that polyphenols drive part of the Mediterranean diet’s effect, so more should help more. In lab studies, polyphenols such as EGCG from green tea and urolithins (made by gut bacteria from walnut compounds) calm inflammatory signaling and support the body’s own antioxidant defenses. Most polyphenols reach the colon, where gut bacteria turn them into other compounds; in laboratory and animal studies, some of these reach the brain. The trial’s larger drop in C-reactive protein in the green group fits this idea, but doesn’t prove it.

What we know about Mankai

Most Mankai research comes from the DIRECT-PLUS team, and several of the studies list ties to the company that produces it.

  • Protein: It contains all nine essential amino acids. In a trial of 36 men, a 30 g protein portion of Mankai raised blood essential amino acids much like cheese or peas did (Kaplan 2019).
  • Iron: In DIRECT-PLUS, haemoglobin and blood iron rose slightly in the green group; in rats, Mankai iron reversed anaemia (Yaskolka Meir 2019).
  • Vitamin B12: It contains active forms of B12, and blood B12 rose more in the green group (15%) than in the others (Sela 2020).
  • Blood sugar: In a crossover study of 20 adults with abdominal obesity (Zelicha 2019), a Mankai shake in place of dinner gave a lower blood sugar peak than a yogurt shake. The two shakes had the same carbohydrate, protein and calories. Fasting glucose was slightly lower the next morning.

It also provides folate, zinc, fiber and polyphenols. Its protein, iron and B12 may help cover gaps in a diet with almost no meat.

Limits of the evidence

  • One trial. DIRECT-PLUS is the main source of evidence. Many promising single-trial findings in nutrition haven’t replicated.
  • A narrow group. Most participants were middle-aged men with metabolic risk factors at one Israeli workplace. Results may not apply to women, older adults or people without metabolic problems.
  • Short for brain aging. 18 months is enough to see MRI changes but short for processes that unfold over decades.
  • No cognitive results. The trial’s main outcomes were metabolic and cardiovascular, and the MRI analyses were secondary. No published data show better memory or thinking on the green diet.
  • Bundled changes. Mankai, green tea and the red meat cut came together, so we can’t tell which one mattered, or whether Mankai is needed at all.

Green-Mediterranean, standard Mediterranean or MIND?

The standard Mediterranean diet has the most replicated evidence for brain health. The green version may add to it but isn’t a proven upgrade yet. If you like green tea and can get Mankai, the green changes are a reasonable choice; if you can’t, you aren’t missing a proven intervention.

The MIND diet takes a different route, emphasizing leafy greens and berries and limiting five food groups. It has more observational evidence, but its trial was null for both cognition and brain MRI. The green-Mediterranean diet has positive MRI findings from one trial and no cognitive trial data. Combining leafy greens and berries from MIND with green tea and walnuts from the green diet covers the core of both.

Frequently asked questions

Can I take a polyphenol supplement instead?

It isn’t a substitute for the diet. Supplements deliver isolated compounds that may not act like whole foods, and the diet’s effects likely come from many compounds, fiber and less red meat working together. High-dose green tea extract (EGCG) supplements have been linked to cases of liver injury, and any supplement can interact with medicines, so ask a doctor or pharmacist first.

Do walnuts alone help cognition?

Not on their own, as far as trials show. In the two-year WAHA trial of 708 older adults (Sala-Vila 2020), walnuts did not improve cognition; a benefit appeared only in a post hoc analysis of the Barcelona site.

Sources

  • Kaplan, A., Zelicha, H., Yaskolka Meir, A., Rinott, E., Tsaban, G., Levakov, G., … & Shai, I. (2022). The effect of a high-polyphenol Mediterranean diet (Green-MED) combined with physical activity on age-related brain atrophy: the Dietary Intervention Randomized Controlled Trial Polyphenols Unprocessed Study (DIRECT PLUS). The American Journal of Clinical Nutrition, 115(5), 1270–1281. doi:10.1093/ajcn/nqac001

  • Pachter, D., Kaplan, A., Tsaban, G., Zelicha, H., Meir, A. Y., Rinott, E., … & Shai, I. (2024). Glycemic control contributes to the neuroprotective effects of Mediterranean and green-Mediterranean diets on brain age: the DIRECT PLUS brain-magnetic resonance imaging randomized controlled trial. The American Journal of Clinical Nutrition, 120(5), 1029–1036. doi:10.1016/j.ajcnut.2024.09.013

  • Tsaban, G., Yaskolka Meir, A., Rinott, E., Zelicha, H., Kaplan, A., Shalev, A., … & Shai, I. (2021). The effect of green Mediterranean diet on cardiometabolic risk; a randomised controlled trial. Heart, 107(13), 1054–1061. doi:10.1136/heartjnl-2020-317802

  • Rinott, E., Meir, A. Y., Tsaban, G., Zelicha, H., Kaplan, A., Knights, D., … & Youngster, I. (2022). The effects of the Green-Mediterranean diet on cardiometabolic health are linked to gut microbiome modifications: a randomized controlled trial. Genome Medicine, 14(1), 29. doi:10.1186/s13073-022-01015-z

  • Yaskolka Meir, A., Rinott, E., Tsaban, G., Zelicha, H., Kaplan, A., Rosen, P., … & Shai, I. (2021). Effect of green-Mediterranean diet on intrahepatic fat: the DIRECT PLUS randomised controlled trial. Gut, 70(11), 2085–2095. doi:10.1136/gutjnl-2020-323106

  • Zelicha, H., Kaplan, A., Yaskolka Meir, A., Tsaban, G., Rinott, E., Shelef, I., … & Shai, I. (2019). The effect of Wolffia globosa Mankai, a green aquatic plant, on postprandial glycemic response: a randomized crossover controlled trial. Diabetes Care, 42(7), 1162–1169. doi:10.2337/dc18-2319

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