in healthy adults at risk for dementia, results of a new randomized trial show.
Given the strong base of evidence from observational studies that demonstrate the benefits of the MIND diet on cognitive decline, Alzheimer’s disease (AD), and neuropathologic changes such as reduced beta amyloid and tau associated with AD, the study’s results were “unexpected,” study investigator Lisa L. Barnes, PhD, with the Rush Alzheimer’s Disease Center, Chicago, said in an interview.
“One possibility is the trial may not have been long enough to see an effect. It’s also possible that participants in the control diet group benefited just as much as those in the MIND diet group because they also improved their diets to focus on weight loss,” Dr. Barnes said.
“Although we did not see a specific effect of the MIND diet, people in both groups improved their cognitive function, suggesting that a healthy diet in general is good for cognitive function,” she added.
The findings were presented at the annual Alzheimer’s Association International Conference and simultaneously published online in the New England Journal of Medicine.
A hybrid of the Dietary Approaches to Stop Hypertension (DASH) and Mediterranean diet, the MIND diet includes foods and nutrients that have been putatively associated with a decreased risk of dementia.
To further investigate, the researchers conducted a randomized trial that included 604 older adults without cognitive impairment who had a family history of dementia, a body mass index greater than 25, and a suboptimal diet determined via a 14-item questionnaire.
For 3 years, 301 were randomly assigned to follow the MIND-diet with mild calorie restriction and 303 to follow a control diet with mild calorie restriction only. All participants received counseling to help them adhere to their assigned diet, plus support to promote weight loss of 3%-5% by year 3.
The primary endpoint was the change from baseline in global cognition and in specific cognitive domains through year 3. Cognition was assessed with an established battery of 12 publicly available cognitive function tests.
The secondary endpoint was the change from baseline in MRI-derived measures of brain characteristics in a nonrandom sample of participants.
“We had good adherence to the assigned diets and both groups lost weight, on average about 5 kilograms in both groups,” Dr. Barnes noted in her presentation.
From baseline through 3 years, small improvements in global cognition scores were observed in both groups, with increases of 0.205 standardized units in the MIND-diet group versus 0.170 standardized units in the control-diet group.
However, in intention-to-treat analysis, the mean change in score did not differ significantly between groups, with an estimated mean difference at the end of the trial of 0.035 standardized units (P = .23).
At the trial’s conclusion, there were also no between-group differences in change in white-matter hyperintensities, hippocampal volumes, and total gray- and white-matter volumes on MRI.
Dr. Barnes noted that the trial was limited to well-educated, older adults, mostly of European descent. Other limitations include the small sample size of those who received MRI and follow-up that was shorter than a typical observational study.
Dr. Barnes noted that this is a single study and that there needs to be more randomized trials of the MIND diet that, as with the observational research, follow participants for a longer period of time.