Best Diets for Preserving Brain Health Identified

Damian McNamara

March 12, 2019

High adherence to a Mediterranean or to A Priori Diet Quality Score (APDQS) diet is associated with better cognitive skills in midlife, whereas adherence to the DASH diet, which is designed to lower blood pressure, is not.

In a large longitudinal study comparing the effect of the three diets on cognition, investigators found those who closely followed the Mediterranean diet (MedDiet) were less likely to experience cognitive decline compared with their counterparts with low adherence. The same was true for those with high adherence to the APDQS diet.

In contrast, good adherence to the DASH diet appeared to have relatively small impact on the preservation of cognitive skills.

"Maintaining healthy dietary practices during adulthood could be an important way to preserve cognitive abilities at middle age," principal investigator Claire McEvoy, PhD, RD, a lecturer in nutrition and aging research at the Institute for Global Food Security, Centre for Public Health Queen's University Belfast in Northern Ireland, told Medscape Medical News.

"While we don't yet know the ideal combinations of foods for a brain-healthy diet, a heart-healthy diet rich in fruit, vegetables, legumes, and nuts; moderate in fish; low-fat dairy foods and alcohol; and low in meat and processed foods could be recommended to patients," she said.

The findings were published online March 6 in Neurology.

Similarities and Differences

The three heart-healthy diets overlap in their recommendations and share some commonalities.

The MedDiet emphasizes whole grains, fruits, vegetables, healthy unsaturated fats, nuts, legumes, and fish — and limits red meat, poultry, and full-fat dairy.

The APDQS emphasizes fruits, vegetables, legumes, low-fat dairy, fish, and moderate alcohol — and limits fried foods, salty snacks, sweets, high-fat dairy, and sugar-sweetened soft drinks.

The DASH diet highlights grains, vegetables, fruits, low-fat dairy, legumes and nuts — and limits meat, fish, poultry, total fat, saturated fat, sweets, and sodium.

It is unclear why the DASH diet did not show a link to better cognition, the researchers note.

"While the dietary patterns are plant-based and similar in respects, there are a number of differences in both the types and amounts of foods consumed," McEvoy said.

One possibility is that DASH does not consider moderate alcohol intake as part of the dietary pattern, whereas the other two diets do.

"It's possible that moderate alcohol consumption as part of a healthy diet could be important for brain health in middle age, but further research is needed to confirm these findings," she added.

Consistent Cognitive Outcomes

For the study, the investigators assessed 2621participants (57% women; 45% black; mean age at baseline, 25 years) in the Coronary Artery Risk Development in Young Adults (CARDIA) trial.

Participants completed diet questionnaires at baseline and at a mean of 32 years and 45 years of age. Researchers then calculated mean diet scores to classify participants into low-, medium-, and high-adherence groups.

They also tested cognitive function twice, when participants were approximately 50 and 55 years old.

Composite cognitive function and cognitive z Scores were based on verbal memory from the Rey Auditory Verbal Learning Test, processing speed from the Digit Symbol Substitution Test, and executive function based on Stroop Interference test and the Montreal Cognitive Assessment (MoCA).

Results showed a link between higher MedDiet scores and less decline in cognitive function.

Cognitive performance decreased in the low scoring/low adherent group by 0.04 points, whereas in the middle and high scorers it increased by 0.03 points. The difference between the low and high adherence groups was statistically significant (P = .03).

Similarly, among the APDQS diet cohort, cognitive function in the low-score group decreased by 0.04 points, remained the same for the middle group, and increased by 0.06 points in the high group (P < .01).

Results on the Stroop Interference test aligned with these findings. For example, the researchers found improvements in performance when comparing the high and low score groups for the MedDiet (low, 0.09 vs high, −0.03) and APDQS diet groups (low, 0.10 vs high, −0.09). Both findings were statistically significant (P < .01).

Synergistic Effects?

In terms of poor global cognitive function, defined as one standard deviation or more below the mean MoCA score, results were once again consistent.

The odds ratios when comparing extreme tertiles of diet scores were 0.54 (95% confidence level [CI], 0.39 - 0.74) for the MedDiet group, 0.48 (95% CI, 0.33 - 0.69) for the APDQS group, and 0.89 (95% CI, 0.68 - 1.17) for the DASH group.

"DASH was not associated with change in cognitive performance," the researchers write.

They adjusted the results for level of education, smoking, diabetes, and physical activity.

Although the diets associated with greater cognition in midlife shared some features, including higher intake of fruit and vegetables, the benefits are likely synergistic.

"There were no strong associations between any of the individual food components of dietary patterns examined and cognitive performance," McEvoy said.

"It appears that the combination of foods that make up the overall diet are most important for brain health," he added.

McEvoy noted that further studies are necessary to determine the effect of changing dietary behavior on brain health across the lifespan, as well as to understand the mechanisms driving the benefits to brain health.

DASH Findings a Surprise

Commenting on the findings for Medscape Medical News, Thomas Vidic, MD, neurologist at Elkhart Clinic, Indiana, said the study adds to evidence supporting the benefits of a healthy diet.

"If you take care of your body, including eating healthier, you can lower your risk of [cognitive] decline," said Vidic, who was not involved in the study.

It makes sense that the MedDiet and APDQS diet made a positive difference, he added. The surprising finding is that the DASH diet did not, "even though I think they expected it to."

In terms of patient counseling, Vidic said these confirmatory data provide clinicians with the most up to date information.

In an accompanying editorial, Gene L. Bowman, ND, MPH, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, and Nikolaos Scarmeas, MD, PhD, National and Kapodistrian University of Athens, Greece, note that the findings "indicate that the MedDiet and APDQS diet offer benefit to cognitive health, while associations for the DASH diet were mostly insignificant."

The editorialists applauded the researchers for evaluating "the large and racially diverse" CARDIA study.

They also point out that the authors "reasonably controlled" for potential confounders and that they repeated the dietary questionnaires at different time points for each participant, which "can improve the accuracy of the subjective reporting of dietary intake."

However, the observational design of the study raises questions about causality, Bowen and Scarmeas note. The "relatively short duration of follow-up" between cognitive assessments was another potential limitation.

The research also could have benefited from objective biochemical measures of the diets to substantiate the findings and to uncover potential mechanisms of action, they add.

The study was supported by the National Heart, Lung, and Blood Institute and the National Institute on Aging. Although McEvoy, Vidic, and the editorialists have reported no relevant financial relationships, McEvoy reports receiving support from the A Beeson-CARDI Fellowship from the American Federation of Aging Research.

Neurology. Published online March 6, 2019. Abstract, Editorial

Follow Damian McNamara on Twitter: @MedReporter.

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