MIND diet surprises scientists, but the result is different from what was expected

Results of the long-awaited Mediterranean diet clinical trial of dietary approaches to preventing hypertension (DASH ) and the diet for intervention in neurodegenerative delay, or also known as the diet MIND – specifically designed to stimulate the brain – are available, and they are less stellar than anticipated.

“We really expected the MIND diet to have a greater effect than the control group, so we were quite surprised by the result,” said study lead author Lisa Barnes, associate director of the Alzheimer’s Disease Research Center at Rush University Medical Center in Chicago.

The MIND diet improved the brains of those who followed it for three years. At the end of the study, the MRI scans showed less white matter hyperintensities (small lesions) and a greater volume of gray matter (the brain’s cognitive center) and white matter (the brain’s communication pathway).

But here’s the catch – the brains of the control group who weren’t following the MIND diet also improved to a similar degree.

Previous studies have shown that both the MIND diet and the Mediterranean diet significantly reduced the risk of cognitive decline and Alzheimer’s disease. However, many of the studies were much longer in duration, Barnes said.

“My main concern with this study from the beginning was that three years may be too short a time to impact a disease process that develops over many decades,” said nutrition researcher Dr. Walter Willett, professor of epidemiology and nutrition at Harvard TH Chan School of Public Health and professor of medicine at Harvard Medical School.

Willett pointed to an older clinical trial that found that eating more beta carotenoids, the antioxidants found in red, yellow, orange and dark green fruits and vegetables, produced cognitive benefits — but only after years of dieting.

“After 15 years or more of beta-carotene supplementation, there was significantly better cognitive function in the beta-carotene group compared with placebo, but after just a few years there was no difference,” said Willett, who was not involved in the new study.

In addition, people in the new study’s control group may have improved their own diet instead of following instructions to eat as they always have, said Barnes, who presented his paper Tuesday at the 2023 International Alzheimer’s Conference in Amsterdam.

“It’s not like people who were on the control diet were unchanged,” she said. “Everyone was eating healthier, losing weight, and so everyone got better. My conclusion is that regardless of type, a healthy diet appears to improve cognitive function.”

It’s difficult to do a long-term clinical trial in nutrition because people can sense which branch of study they’re on, said Dr. David Katz, an expert in preventive medicine and lifestyle who founded the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine. He was not involved in the study.

“Study enrollment likely raised awareness of prudent dietary practices to protect cognition among people already concerned about this,” Katz said. “This study did not rule out a difference; simply failed to confirm one.”

What is the MIND diet?

Developed in 2015 by researchers at Rush University in Chicago, the MIND diet embodies much of the plant-based Mediterranean diet, which focuses on fruits, vegetables, whole grains, beans, seeds, nuts and lots of extra virgin olive oil. Red meat and sweets are rarely eaten, but fish, rich in omega-3 fatty acids, is a staple food.

The MIND diet also borrows elements from the DASH diet (Dietary Approaches to Prevent Hypertension Diet). The DASH diet focuses on lowering blood pressure and cholesterol, which when off-set can lead to heart attacks, strokes, and constriction of small blood vessels that can lead to dementia. The standard DASH diet limits salt to 2,300 milligrams a day, less than a teaspoon of salt.

Numerous studies have found that the Mediterranean diet can reduce the risk of diabetes, high cholesterol, dementia, memory loss, depression and breast cancer. The diet, which is more of an eating style than a strict diet, has also been linked to stronger bones, a healthier heart and a longer life. The DASH diet has been shown to lower blood pressure and is the American Heart Association’s top diet.

The MIND diet takes Mediterranean diets and DASH to the next level by focusing on foods known to boost brain health. Dark leafy greens should be eaten every day of the week on the MIND diet. This includes arugula, kale, dandelion greens, escarole, grape leaves, kale, mustard greens, romaine lettuce, spinach, Swiss chard and turnip greens.

Berries are also highlighted over other fruits on the MIND diet. Blackberries, blueberries, raspberries or strawberries should be eaten at least five days a week.

In addition, three servings of whole grains should be eaten daily. Beans should be consumed in four meals a week, poultry in two and fish at least once a week. Eat nuts five times a week and avoid butter, cheese, red meat, fried foods, pasta and sweets.

A 2017 study of nearly 6,000 healthy older Americans, with an average age of 68, found that those who followed the Mediterranean MIND diet reduced their risk of dementia by a third.

Both groups lost weight

The study, published Tuesday in the New England Journal of Medicine, followed 604 overweight people over age 65 for three years. All had a first-degree relative with Alzheimer’s disease and were cognitively normal at baseline.

The experimental group was asked to follow the MIND diet and at the same time cut 250 calories a day with the help of a counselor. Vitamin supplements were not allowed. This group received appropriate amounts of olive oil, blueberries and nuts each month.

The control group was told to continue eating their regular vitamin-free diet, but also to try to cut 250 calories a day with the help of counseling. They received gift cards for $30 a month.

A battery of cognitive tests was taken when the study began and repeated at set intervals, while regular blood tests measured biomarkers, such as beta-carotene, which indicated how well each person was following the MIND diet.

When diet quality was assessed at baseline, both groups were equal. At the end of six months, however, people who followed the MIND diet improved their diet quality score by more than three points — which was maintained for three years — while the control group improved by less than one point.

At the end of the study, people in both groups lost ten pounds.

“The ten-pound weight loss in both groups is impressive, better than many weight loss trials,” said Willett. “It’s clear that the control group was making dietary changes.”

Blood tests found that levels of carotenoids, such as beta-carotene, were much higher at baseline in the group eating the MIND diet, but the increase “wasn’t sustained over time and through most of the trial was real but modest,” Willett said.

Vegetables and fruits are the main sources of carotenoids and “also appear to be the most important component of the Mediterranean diet for cognitive function,” said Willett. “The test provided olive oil and nuts, but not vegetables, so it should not be surprising that differences in carotenoids were not maintained.”

Such results, while disappointing, do not mean that the much research on the benefits of the Mediterranean and DASH diets has been refuted, experts say. Quite the opposite.

Katz points to the “Blue Zones,” areas of the world where people typically live long, healthy lives, up to and beyond age 100. “All Blue Zone residents experience very low rates of dementia up to age 100, but they have very varied diets,” said Katz, who has published research on using food as preventive medicine.

“We have ample reason to suspect that more than one high-quality diet, not just MIND, would confer comparable benefits.”