MIND Diet Trial Reports Brain Findings

AMSTERDAM — Changes in cognition and brain MRI outcomes did not differ significantly over 3 years in overweight or obese people with a family history of dementia who followed the MIND diet — a hybrid of the Mediterranean diet and the DASH (Dietary Approaches to Stop Hypertension) diet — compared with those who followed a control diet with mild caloric restriction, the phase III MIND trial showed.

Global cognition scores improved in both groups from baseline to year 3, with increases of 0.205 standardized units in the MIND-diet group and 0.170 standardized units in the control group (mean difference o0.035 standardized units with higher scores indicating better cognitive performance, P=0.23).

Changes in white-matter hyperintensities, hippocampal volumes, and total gray matter and white matter volumes on MRI were similar in the two groups, reported Lisa Barnes, PhD, of Rush University Medical Center in Chicago, at the 2023 Alzheimer’s Association International Conference. Results were published simultaneously in the New England Journal of Medicine.

The MIND diet emphasizes green leafy vegetables and berries, incorporating foods that have been associated with a decreased risk of dementia in observational studies.

“There’s considerable evidence from observational studies that have linked diet to Alzheimer’s disease prevention and brain health,” Barnes said. “But the randomized control trials of dietary interventions for brain health have been somewhat mixed, and most of them have been of supplements or single nutrients.”

“We know that foods are not eaten in isolation,” Barnes pointed out. “Dietary patterns have been become increasingly important.”

The primary outcome of the MIND trial was cognitive change assessed by a global cognition score and four cognitive domain scores. All were derived from a 12-test battery that included executive function, episodic memory, semantic memory, and perceptual speed measurements. The study’s secondary outcome was brain changes on MRI in a random selection of participants.

Participants were ages 65-84 without cognitive impairment at baseline, were overweight or obese with a BMI of 25 or more, and had a self-reported family history of dementia. They also had suboptimal diets, defined as a MIND-diet score of 8 or less based on a 14-item diet questionnaire created by the investigators.

The study started recruiting in Chicago and Boston in March 2017, randomizing 301 people to the MIND-diet group and 303 people to controls. Mean age of participants was 70; about 65% were women, 88% were white, and 11% were Black. A total of 201 participants had follow-up imaging at year 3.

Both groups were encouraged to follow mild caloric restrictions with of goal of consuming 250 kcal less per day. They received counseling to help them adhere to their assigned diet, and had support to promote a target weight loss of 3%-5%. Those in the MIND-diet group received a monthly supply of extra virgin olive oil, blueberries, and mixed nuts. Controls received $30 grocery store gift cards each month.

“Right before our third year, we had to halt study operations for about 3 months, as [COVID-19 pandemic] lockdown orders were in both in Chicago and Boston,” Barnes noted. “We switched to telephone assessments for people who did not want to return to the office.”

At baseline, the mean MIND-diet score was 7.7 in the MIND-diet group and 7.8 in controls. At 6 months, participants in the MIND-diet group increased their score by 3.3 points to a mean score of 11.0; their score stayed at about that level throughout the trial. Controls increased their MIND-diet score by 0.7 points, to a mean score of 8.5.

Analyses of blood antioxidant nutrient levels, including lutein, zeaxanthin, and alpha and beta carotene, showed MIND-diet participants adhered to their plan. In each group, participants lost about 5.0 kg (around 11 lbs) of body weight during follow-up.

“In post-analysis, we looked at the change in diet before the pandemic and at the end of the trial,” Barnes said. “At year 2 — before the pandemic — there was a suggestive effect of the MIND diet that was just marginally significant.”

It’s possible weight loss was an important component for both groups, Barnes noted. “The observational studies don’t really bear that out, but we speculated that could have been possible in this trial,” she said.

The trial involved a well-educated older adult population, mostly of European descent, Barnes acknowledged. “We had a small sample size of those who received MRI,” she said. “And our follow-up was shorter than a typical observational study.”