The latest findings about the cognitive effects of the well-known MIND diet come from a much-anticipated randomized controlled trial, the gold standard of scientific evidence.
The results, however, published July 18 in the New England Journal of Medicine, were unexpected. The MIND diet wasn’t more effective than the control diet at improving cognition.
For people who, like me, have tracked the findings of previous MIND diet studies, these new results might have come as a bit of a blow.
Here’s what to know.
What is the MIND diet?
The MIND diet, short for Mediterranean-DASH Diet Intervention for Neurodegenerative Delay, is a hybrid of the Mediterranean diet and the DASH (Dietary Approaches to Stop Hypertension) diet. Both eating plans emphasize whole plant foods and limit animal foods and saturated fat.
The diet has been modified to include specific foods associated with a lower risk of dementia including berries, leafy greens, oily fish and extra virgin olive oil.
The MIND diet first made headlines in 2015 when researchers from the Rush University Medical Center in Chicago published two observational studies conducted in roughly 900 community-living older adults.
One study linked following the MIND diet, even moderately, to protection against Alzheimer’s disease. The other study associated the MIND diet with a slower rate of cognitive decline.
Since then, studies have associated the MIND diet with positive effects on brain aging, including preventing the build-up of beta-amyloid plaques in the brain, a hallmark sign of Alzheimer’s disease.
It’s thought that foods in the MIND diet deliver potent antioxidant and anti-inflammatory effects that protect brain functioning and guard against cognitive decline.
The MIND diet randomized controlled trial
The three-year MIND diet trial was conducted by researchers from Rush University Medical Center and Harvard Medical School.
A total of 604 adults, 65 and older, who were overweight and had a suboptimal diet were enrolled. All were cognitively unimpaired but had a family history of dementia (first degree relative).
The study compared the MIND diet with a small calorie deficit (250 fewer calories a day) to a control diet with the same caloric deficit to test its effects on cognitive decline and brain-imaging markers of dementia and Alzheimer’s disease.
Participants assigned to the MIND diet were instructed to incorporate MIND diet foods and use MIND diet recipes. They were also taught behavioural strategies to lose weight.
Those in the control group were focused on portion control, calorie-tracking and behavioural weight loss strategies, without changing the types of foods they usually ate.
All participants received counselling by registered dietitians during the study.
Participants also took a battery of 12 cognitive tests at the start of the study and at regular intervals throughout. Two hundred of the study participants underwent brain imaging at the beginning and end of the trial.
The trial results
At the starting point, the diet quality of participants in both groups was the same – both groups had an average MIND-diet score of 7.7 (out of a possible 14).
After six months, the MIND-diet group improved their score by 3.3 points and maintained this level for the rest of the trial. The MIND-diet score of the control group increased by less than one point.
Participants in both groups lost, on average, 11 pounds during the study.
After three years, small improvements in overall cognitive scores were observed in both the MIND-diet group and the control group.
But there was no significant difference between the two groups’ scores. Following the MIND diet didn’t result in a cognitive effect greater than the control group, which the researchers had expected to find.
The brain scans of participants in both groups also suggested slight improvements. This finding, however, wasn’t statistically significant, meaning it could have occurred by chance.
Discrepancy from previous MIND diet findings
Keep in mind this is one study. And there are possible reasons why the MIND diet didn’t produce a stronger cognitive benefit.
Three years may have been too short; a longer time period adhering to the MIND diet may have made a greater impact. Past studies linking diet to a lower risk of cognitive decline have been much longer.
Knowing you’re enrolled in a study assessing cognitive function could also make you more likely to make food choices that protect brain health.
Individuals in the control group likely improved their diet even though they weren’t supposed to. Given the 11-pound weight loss, this seems to be the case.
These new findings do not mean the MIND diet doesn’t benefit brain health. This trial showed it made a small positive difference over three years.
The new findings also don’t invalidate the results from many past studies that have tied cognitive benefits to the MIND and Mediterranean diets.
According to Dr. Lisa Barnes, lead study author and associate director of the Alzheimer’s Disease Research Center at Rush University Medical Center, “the results are suggestive of a benefit of a healthy diet, regardless of the type; both groups improved.”
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD