A recent study published in The New England Journal of Medicine evaluated the effects of a three-year dietary intervention on cognitive decline in older adults.
Study: Trial of the MIND Diet for Prevention of Cognitive Decline in Older Persons. Image Credit: SewCreamStudio/Shutterstock.com
Background
Lifestyle interventions targeting diets can influence public health. Many trials have analyzed comprehensive diets, mainly focused on cardiovascular health. Such interventions include the Mediterranean diet and dietary approaches to stop hypertension (DASH).
However, data on brain health interventions are limited. The Mediterranean-DASH intervention for neurodegenerative delay (MIND) is a hybrid of the Mediterranean and DASH diets.
MIND incorporates many DASH and Mediterranean diet components and some modifications to include foods putatively linked to slower cognitive decline and lower risk of Alzheimer’s disease.
It emphasizes the use of plant-based foods, nuts, olive oil, and fish and limits the consumption of foods with high sugar and saturated fat, such as whole-fat cheese, sweets, fried foods, pastries, butter, and processed or red meat.
About the study
In the present study, researchers conducted a randomized controlled trial of the MIND diet in older adults. Individuals aged 65 or above were eligible if they were overweight, scored at least 22 on the Montreal cognitive assessment, reported a family history of Alzheimer’s dementia, and had sub-optimal diets. Subjects were recruited in Boston and Chicago, the United States (US), between January 2017 and April 2018.
An initial screening was performed to obtain data on age, diet quality, family history of dementia, food allergies, use of medications for Parkinson’s or Alzheimer’s disease, and nutritional supplements. Participants were randomized to the MIND diet group with mild caloric restriction for weight loss or the usual diet (control) group with the same caloric restriction.
Baseline assessments included weight, height, blood pressure measurements, cognition tests, food-frequency questionnaires, and 24-hour dietary recall. After baseline assessments, participants were assigned to the diet group and instructed to follow the diet for three years.
All participants received dietary counseling throughout the trial. The MIND diet group received monthly supplies of blueberries, extra virgin olive oil, and mixed nuts.
Control participants received monetary gift cards at the same time. Participants had at least five opportunities to connect with others in the same group during group sessions on dietary education, motivational activities, and tips to promote weight loss.
Short-term measures included weight assessments, a MIND diet questionnaire, a food-frequency questionnaire, and personalized goals.
The primary endpoint was the change in global cognition relative to baseline. Twelve tests assessed cognition at six, 12, 24, and 36 months.
Secondary endpoints included changes in imaging-derived volumetric measures of the brain, hippocampus, and white-matter hyperintense lesions relative to baseline. All participants were offered to undergo magnetic resonance imaging (MRI) at the start of the trial. MRI was performed at baseline and three years.
Findings
The researchers assigned 301 and 303 participants to the MIND- and control-diet groups, respectively. Baseline characteristics were similar between groups, except there were more control participants with an apolipoprotein E ε4 allele.
Type 2 diabetes and hypertension were the most common coexisting conditions, with similar prevalence between groups.
The average MIND diet score at baseline was 7.7 and 7.8 in the MIND and control groups, respectively. MIND-diet subjects increased this score by 3.3 points to an average score of 11 at six months and maintained it throughout the trial.
On the other hand, controls increased it by 0.7 points. Results of biochemical analyses supported MIND diet adherence. Both groups showed weight loss from baseline.
The average change in global cognition score from baseline through the third year was 0.205 and 0.17 standardized units among MIND diet and control subjects, respectively. At baseline, 267 subjects underwent MRI; 201 underwent a follow-up MRI at three years.
The volume of white-matter hyperintense lesions increased in both groups by the end of the trial, whereas total brain and hippocampal volumes decreased.
The researchers did not observe any appreciable effect of the MIND diet on brain volumetric changes relative to the control diet. The incidence of adverse events was similar between groups during the trial. Cardiovascular and musculoskeletal events were the most common adverse events.
Overall, ten deaths were recorded; adverse events and deaths were unrelated to the dietary intervention.
Conclusions
MIND-diet participants had minor improvements in global cognition, similar to those following a control diet. It is plausible that the practice effects of cognitive testing could account for improvements in both groups.
Moreover, it is possible that the intervention may not improve cognitive function or may require a longer period of adherence to have an effect. Notably, most participants were of European descent, limiting generalizability.
In sum, no significant differences in cognition and brain imaging were observed between MIND- and control-diet participants in this trial.
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