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The Best Diet to Maintain Your Brain

A Mediterranean diet pumped up with plant polyphenols could delay brain aging.

Tashka2000/iStock, Popova Photo/iStock
Tashka2000/iStock, Popova Photo/iStock

The likelihood that an American will be a centenarian is today twice what it was two decades ago. The numbers are still small—about 90,000 in 2020, up from 50,000 in 2000—but they’re definitely on an upward trajectory. Credit, at least in part, a growing awareness of disease risk factors—smoking being the most notable one—especially for cardiovascular disease, still the single largest cause of death (33 percent) among the aging.

The prevalence of age-related dementia is declining among Americans as well. And for the same reason, apparently—education; awareness encourages people to protect their health. But before you break out the champagne, consider a sobering statistic from the Alzheimer’s Association: One in three seniors still dies with some form of dementia.

Age, of course, is the strongest risk factor for neurodegenerative conditions. The brain normally shrinks with age, starting at midlife, and there are changes at every level, from molecules to memory: loss of neurons; contraction of dendrites; reduced synaptic plasticity; and degeneration of the myelin sheath that covers the axons (which together make up the brain’s white matter), disrupting the transmission of nerve signals. Decline starts in the cognitively critical frontal cortex—last to mature, first to go—but it winds up being most pronounced in the cortex, the movement-necessary cerebellum, and the hippocampus, the brain’s learning center and memory storage site.

But not everyone succumbs. The New England Centenarian Study suggests there are “escapers,” who have no clinically detectable disease of any kind at 100, and “delayers,” who show no signs of any age-related disease until 80 or older. For these lucky folks, it is thought, morbidity gets compressed at the tippy end of the life span.

One of the most notable features of the brain is its furious consumption of energy. Although it accounts for 2 percent of body weight, it is so metabolically active that it burns 20 percent of the body’s fuel.

A great deal of evidence suggests that cognitive decline, including Alzheimer’s disease, may be a metabolic disorder, a disturbance in fuel operations by the brain. This process loses efficiency with age and is inherently influenced by what we eat. The very earliest changes caused by Alzheimer’s disease are those affecting glucose, the brain’s primary fuel, researchers find.

The raging metabolic furnace of the brain spews out highly unstable free radicals of oxygen that damage the machinery of cells and their protective membranes, the cumulative effects of which show up as slowing of functions and memory problems. A vigorous antioxidant defense is an essential way of buttressing the brain against neurodegeneration.

This likely explains why studies link the Mediterranean diet to longevity in general and to protection against dementia specifically—low rates of brain atrophy, reduced rates of Alzheimer’s disease, and improved cognitive function. Compared to the standard Western diet, the Mediterranean diet features less meat, especially less red and processed meat, in favor of fish; fewer simple carbohydrates; greater amounts of monounsaturated fats, notably olive oil; and significantly more plant-based foods, not just fruits and vegetables but whole grains and nuts.

The shift to plant-based foods ensures that a steady supply of agents is available to disarm free radicals, stimulate the removal of any damaged biomolecules before they gum up cellular operations, and maintain brain function. Fruits and vegetables are naturally rich in substances that act as antioxidants, notably polyphenols. Thousands of them are produced in plants to limit the damage done by adverse environmental conditions, from poor soil and drought to excess sun and infestation by bugs.

Consumed by humans, plant-based polyphenols can cross the blood-brain barrier, reduce oxidative stress, and ameliorate inflammation. They can also increase cerebral blood flow, induce neurogenesis and plasticity in the hippocampus, and maintain the integrity of the white matter.

Good as the Mediterranean diet is, could its effects be even further amplified? A team of researchers from Harvard, the University of Leipzig in Germany, and Ben Gurion University, led by Israel’s Iris Shai, has tweaked the standard Mediterranean diet by nearly tripling the amount of polyphenols it supplies, creating the Green Mediterranean diet.

In a study of 284 people, all with abdominal obesity, the team randomly assigned participants to follow either healthy dietary guidelines, the standard Med diet, or the Green Med version for 18 months. The participants were middle-aged, averaging 50 years—just when brain atrophy accelerates. And all engaged in similar levels of physical activity, provided on-site.

The researchers found that the Green Med diet significantly attenuated brain atrophy, specifically hippocampal loss, as measured by MRI. The effect was correlated with other improvements as well—improved blood glucose control and insulin sensitivity, weight loss, and decreased blood pressure. White matter integrity improved, too.

Both Med diet groups consumed 28 grams a day of walnuts, providing 440 mg/day of polyphenols. What distinguishes the Green Med diet is further provision of 1,240 mg/day of polyphenols: three to four cups daily of green tea, rich in the polyphenol epigallocatechin gallate; and 100 grams of duckweed, an aquatic plant traditionally consumed as a vegetable in Southeast Asia. It grows all over the world in still waters, and ducks and geese normally feed on it. It contains not only 200 polyphenols (among them kaempferol, quercetin, and catechin) but, unusual for a plant, complete protein, with all nine essential amino acids. It’s also rich in fiber, B vitamins, and minerals.

The study incorporated a strain of duckweed called mankai, specially developed to be protein rich. Participants drank a green duckweed shake a day. The plant allows the Green Med diet to be as distinguishable for what’s not in it—red and processed meat—as what it includes. The less meat participants consumed, the less brain atrophy they had.

The researchers believe that long-term polyphenol enhancement potentiates the effects of a healthy lifestyle (physical activity and a Mediterranean diet). They deem it “a powerful strategy to halt or even reverse the progression” of both cognitive and cardiometabolic decline.

Polyphenols are especially abundant in cocoa, berries, and spices such as cloves, as well as red wine, black olives, and green tea. They are also widely available as supplements.

Dementia Data

  • In 2021, about 6.2 million U.S. adults aged 65 or older lived with dementia.
  • Among men, the prevalence of dementia is 7.0 percent; among women, 9.7 percent.
  • Age-related brain atrophy is more pronounced in males than females and starts earlier.
  • Hippocampal atrophy accelerates around age 55.
  • Hippocampal atrophy begins years before there are clinical manifestations of cognitive decline.
  • Mental processing speed is one of the earliest cognitive abilities to decline.
  • Physical activity is neuroprotective because it is cognitively stimulating, requiring multitasking, navigation, and spatial memory.
  • While rates of age-related dementia are generally declining in the U.S., rates of early-onset dementia (before age 65) are increasing.

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