Reference: N Engl J Med. 2023 Aug 17;389(7):602-611
Practice Point: The MIND diet (a combination of the Mediterranean and DASH diets) does not seem to improve cognitive function in older adults any more than a healthy diet with nutritional support.
EBM Pearl: Nutritional research is tough, and even with RCTs there may be multiple factors to consider in both the methodology and outcome analysis.
The MIND diet, short for Mediterranean-DASH Intervention for Neurodegenerative Delay, combines elements of the Mediterranean and DASH diets. It’s a little like a DASH diet that emphasizes weekly fish consumption. Unlike the Mediterranean and DASH diets, the MIND diet does not stress daily fruit intake, has separate components for berries and nuts, and promotes regular consumption of green leafy vegetables. Observational studies have suggested that the MIND diet may be associated with a reduction in dementia risk, but is this finding still supported in higher quality trials? A recent trial in NEJM helps to answer that question.
The authors of this randomized controlled trial enrolled 604 adults aged ≥ 65 without cognitive decline but with a family history of dementia, BMI > 25, and a suboptimal diet (measured by a MIND score ≤ 8). Participants were recruited after responding to an ad and were included only if they were compliant during a 4-week run in a period. Those enrolled were assigned 1:1 to the MIND diet with mild calorie restriction or a similarly calorie-restricted usual diet. The intervention group received a monthly supply of blueberries, mixed nuts, and olive oil. The authors assessed cognition 4 times over 3 years using a battery of 12 established cognitive function tests (including MOCA), covering memory, executive function, and perceptive speed. For 200 participants, investigators also measured total brain volume, hippocampal volume, and white-matter lesions with MRIs before and after the study. Various statistical methods were applied, including linear mixed effect models. At 3 years, 93.4% of participants had completed the study. At the trial’s end, both groups showed cognitive improvement, with a 0.205 standardized unit increase in the MIND-diet group and 0.170 in the control-diet group (mean difference = 0.035, 95% CI = -0.022 to 0.092). The MRI findings were also similar between the two groups.
It’s not too surprising that both of these groups did well, as they received pretty intensive nutrition support with counseling weekly during the first 6 months, every other week during the second 6 months and twice monthly for the remainder of the study. Furthermore, this trial enrolled a very specific group of people who were more likely to do well at baseline: a generally well educated cohort who demonstrated adherence to a calorie restricted diet as a stipulation for trial enrollment. This cherry-picked group might not only limit generalizability, it could bias the results. Lastly, while 3 years is a pretty long trial period in general, longer follow up (and longer adherence) may be necessary to observe an effect on outcomes like cognition.
The memorable takeaway here is that it probably doesn’t hurt to encourage older adults to adopt a healthy lifestyle with a diet rich in antioxidants from foods like green leafy vegetables, nuts, berries, and olive oil, but it doesn’t seem to make an appreciable difference in their cognitive function. Considering that the body of evidence is still relatively small for the MIND diet, further research, especially trials with longer follow up, better controls, and a less biased cohort, would not be unreasonable to more fully evaluate any potential impact this diet may have on cognitive function.
For more information, see the topic Alzheimer Dementia in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Elham Razmpoosh, PhD, Postdoctoral fellow at McMaster University. Edited by Alan Ehrlich, MD, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School; Katharine DeGeorge, MD, MS, Senior Deputy Editor at DynaMed and Associate Professor of Family Medicine at the University of Virginia; Dan Randall, MD, Deputy Editor at DynaMed; Nicole Jensen, MD, Family Physician at WholeHealth Medical; Vincent Lemaitre, PhD, Medical Editor at DynaMed; and Sarah Hill, MSc, Medical Writer at DynaMed.