Polyphenol-rich Mediterranean diets could help keep the brain younger

By Dr. Chinta SidharthanReviewed by Lily Ramsey, LLMNov 6 2024

A new study suggests that Mediterranean and green-MED diets, rich in polyphenols from sources like green tea and Mankai, may slow brain aging and reduce neurodegeneration. Blood sugar control plays a key role in preserving brain volume.

Study: 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. Image Credit: Pacorpi/Shutterstock.com

In a recent study published in The American Journal of Clinical Nutrition, scientists investigated how specific dietary factors affected brain volume relative to chronological age.

Using longitudinal data, they examined the effects of the Mediterranean and green Mediterranean diets on hippocampal occupancy measures to assess brain aging and determine whether improved glycemic control could improve brain health.

Background

The brain undergoes a natural process of shrinkage or atrophy with age, which is also linked to cognitive decline with progressing age. While the natural rate of brain atrophy with age is unavoidable, certain illnesses and conditions, such as type 2 diabetes, inflammation, high cholesterol, and high blood pressure, can accelerate the rate of cognitive impairment and brain atrophy.

Type 2 diabetes has been linked to significant brain atrophy, especially in the hippocampus, which is critical for memory and is also affected by Alzheimer's disease. Individuals with a long history of diabetes often show enlarged brain ventricles and a greater degree of brain atrophy, indicating potential cognitive decline.

The measurement of hippocampal shrinkage relative to ventricle enlargement, known as the hippocampal occupancy score, has been used to monitor the risk of progression of mild cognitive impairment to Alzheimer's disease.

Furthermore, although recent studies have reported that healthy diets such as the Mediterranean diet could slow down age-related brain volume loss, the impact of specific dietary changes, such as improved glycemic control, on brain health remains unclear.

About the study

The present study was based on a previous randomized control trial of dietary interventions, known as the 18-month DIRECT PLUS trial, which was conducted in a workplace setting and enrolled close to 300 participants above the age of 30 years.

The participants all had dyslipidemia or abdominal obesity and were randomly assigned to one of three dietary intervention groups. The health dietary guidelines group was the control, while the other two groups were for the calorie-restricted Mediterranean diet intervention, and the green-Mediterranean diet intervention, which contained a diet rich in polyphenols.

The Mediterranean diet emphasizes the consumption of poultry, fish, and vegetables while reducing the intake of red meat. Both the Mediterranean diet interventions included 28 grams of walnuts per day.

The green-Mediterranean diet focused on polyphenol-rich food, such as 3 to 4 cups of green tea a day, and a Mankai green shake made from duckweed.

Additionally, each group also received specific nutritional guidance and physical activity instructions, and each participant was provided with gym memberships and attended regular instructional sessions on exercise and nutrition.

Several anthropometric and clinical measurements were recorded at the beginning and end of the trial, including blood pressure, weight, height, waist circumference, and fasting blood samples to assess the levels of glucose, insulin, hemoglobin A1c (HbA1c), C-reactive protein, and lipids.

Brain magnetic resonance imaging (MRI) scans were also conducted at baseline and the end of the trial.

The researchers used specialized software to measure the hippocampal and lateral ventricle volumes from the MRI scans, which were used to calculate the hippocampal occupancy score.

This measure served as the primary marker to assess neurodegeneration. Several statistical analyses were conducted to determine the relationship between the dietary interventions and changes in hippocampal occupancy score.

Results

The study found that the Mediterranean diet rich in polyphenols resulted in improved glycemic control after an 18-month-long dietary intervention, and these changes were associated with beneficial effects on brain aging. The green Mediterranean diet was linked to slower age-related neurodegeneration and a younger brain age.

In contrast, simple changes in weight did not have any pronounced impact on brain aging as compared to changes in glycemic control, suggesting an independent benefit on brain health from better glycemic control.

The participants who had lower body mass index, weight, HbA1c levels, and blood pressure at baseline showed more favorable hippocampal occupancy scores.

Furthermore, those who showed significant improvements in fasting glucose, insulin resistance, HbA1c, and C-reactive protein levels after 18 months of the dietary intervention also had the most important improvements in the brain aging metrics.

The green Mediterranean diet, which included Mankai shakes and green tea, resulted in the highest glycemic improvement rate (58.33%). This diet was also associated with notable brain health benefits.

Increased consumption of green tea and Mankai shake was linked to greater improvements in brain health, especially in participants who consumed Mankai shake at least thrice a week and drank green tea daily.

Conclusions

Overall, the study found that a healthy diet, such as the Mediterranean diet, low in red meats and rich in fruits, vegetables, and lean meat, can support brain health by slowing age-related brain atrophy.

These findings also highlighted the potential of polyphenol-rich foods in mitigating age-related neurodegeneration, making them a promising strategy for future interventions for cognitive health.