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Results are in from the highly anticipated clinical trial on the Mediterranean-DASH Diet Intervention for Neurodegenerative Delay or MIND diet — a diet designed specifically to boost the brain — and they are less stellar than anticipated.

“We really expected that the MIND diet would show an effect above the control group, so we were quite surprised by the outcome,” said lead study author Lisa Barnes, associate director of the Alzheimer’s Disease Research Center at Rush University Medical Center in Chicago.

Actually, the MIND diet did improve the brains of those who followed it for three years. At the end of the study magnetic resonance imaging (MRI) scans showed fewer white matter hyperintensities (tiny lesions) and a larger volume of both grey matter (the brain’s cognitive center) and white matter (the brain’s communication highway).

But here’s the rub — the brains of the control group who were not eating the MIND diet also improved to a similar degree.

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

“My main concern with this trial from the beginning has been that three years may be too short a time to have an impact on a disease process that develops over many decades,” said leading nutrition researcher Dr. Walter Willett, a professor of epidemiology and nutrition at Harvard T.H. Chan School of Public Health and professor of medicine at Harvard Medical School.

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

“After 15 or more years of beta-carotene supplementation there was significant and importantly better cognitive function in the beta-carotene group compared to placebo, but after just several 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 sticking to instructions to eat as they always had, said Barnes, who is presenting her paper Tuesday at the 2023 Alzheimer’s International Conference in Amsterdam.

“It’s not like people who were on the control diet stayed flat,” she said. “Everyone was eating healthier, losing weight, and so they all got better. My takeaway is that regardless of the type, a healthy diet does seem to improve cognitive function.”

It’s difficult to do a long-term clinical trial in nutrition because people may realize which arm of the study they are in, said Dr. David Katz, a specialist in preventive and lifestyle medicine 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.

“Enrolling in the study likely heighted awareness of prudent dietary practices to protect cognition among people already concerned about that,” Katz said. “This study did not exclude a difference; it simply failed to confirm one.”

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

The MIND diet also assimilates elements of the Dietary Approaches to Stop Hypertension (or DASH) diet. The DASH diet focuses on lowering blood pressure and cholesterol which 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 table salt.

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

The MIND diet takes the Mediterranean and DASH diets 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. Those include arugula, collards, dandelion greens, endive, grape leaves, kale, mustard greens, romaine lettuce, spinach, Swiss chard and turnip greens.

Berries are also stressed 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 grain should be eaten daily. Beans should be eaten 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 and pastries and sweets.

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

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

The experimental group was asked to follow the MIND diet while also cutting 250 calories a day with the help of a counselor. Vitamin supplements were not allowed. This group was provided with appropriate amounts of olive oil, blueberries and nuts each month.

The control group was told to continue eating their regular diet without vitamins but to also try to cut 250 calories a day with counseling help. They were given $30 gift cards monthly.

A battery of cognitive testing was done when the study started 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 accessed at the start of the study, both groups were equal. By the end of six months, however, people eating the MIND diet improved their diet quality score by over three points — which was maintained for three years — while the control group improved by less than a point. By the end of the study, people in both groups lost five kilograms or 11 pounds.

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

Blood tests found levels of carotenoids, such as beta carotene, were much higher at first in the group eating the MIND diet, but the increase was “not sustained with time and for most of the trial were real but modest,” Willett said.

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

Such results, while disappointing, do not mean that the mountains of research on the benefits of the Mediterranean and DASH diets have been disproven, experts say. Quite the opposite, in fact.

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

“We have ample cause to suspect that more than one very high quality diet, and not just MIND, would confer comparable benefit.”