'MIND diet,' intended to prevent dementia, doesn't offer significant brain benefit, trial suggests

The MIND diet — which is intended to guard against dementia, and is rich in fruits and veggies and low in saturated fats — has no short-term brain benefits beyond those seen in people who follow a standard, "suboptimal" diet, a three-year trial suggests.

The trial's results, published Tuesday (July 18) in The New England Journal of Medicine, showed that participants who followed the MIND diet for three years showed slight improvements in their overall cognition, as measured with a dozen tests. However, those mental improvements were not statistically different from those seen in people who followed their usual diets. 

A subset of people from both the MIND and standard diet groups also underwent brain scans, which revealed that their brains changed in the same ways over the three-year period, regardless of the diet they followed. 

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

Related: Does the Mediterranean diet reduce dementia risk? 20-year study hints no 

The MIND diet, short for "Mediterranean-DASH Intervention for Neurodegenerative Delay" diet, is essentially a mash-up of two other diets hypothesized to improve brain health and reduce the risk of dementia. The broadly defined Mediterranean diet is rich in vegetables, whole grains, legumes, seafood and unsaturated fats like olive oils and low in red meat, eggs, saturated fats and sweets. The Dietary Approaches to Stop Hypertension (DASH) diet is very similar but offers specific daily and weekly nutrition goals and limitations on salt intake.

Large observational studies have linked the MIND diet to a lower rate of Alzheimer's disease and an overall slower rate of cognitive decline in older adults, according to the National Institute on Aging. However, few gold-standard clinical trials have examined this link, and the biological reasons why the MIND diet might have this protective effect have not been clearly demonstrated in humans.

The new trial included 604 adults ages 65 and older who, at the start of the trial, were cognitively healthy but had a family history of dementia. All of the study participants were also overweight and followed "suboptimal" diets, meaning diets that significantly diverged from the MIND diet, at the start of the trial.

The participants were split into two groups that were told to either stick to their usual diet with minor caloric restrictions or to adopt the MIND diet. Both groups received regular dietary counseling, as well as either MIND-compliant foods (for the first group) or money for grocery shopping (for the second). Researchers monitored the participants' weights, diet adherence and blood levels of certain metabolites. 

Ultimately, participants in both groups saw similar cognitive improvements, brain changes and weight loss by the end of the study period.

It's "plausible that practice effects of repeated cognitive testing could account for improvement in both of our trial groups, as has been observed in previous randomized trials," the trial organizers noted in their report. It is also "possible that these interventions do not improve cognitive functioning or that it would take a longer period of adherence for an effect to be observed." 

In short, the study has limitations but hints that, at least in the short term, the MIND diet doesn't offer huge brain benefits over a diet with minimal calorie restrictions.