In this 3-month randomized controlled trial in middle-aged women with obesity, a calorie-restricted MIND diet (which emphasizes natural plant-based foods and limits foods high in saturated fat) improved cognitive performance compared to a calorie-restricted control diet with a similar macronutrient distribution.
Obesity is associated with alterations in cognitive performance and overall brain volume, and obesity in midlife is a risk factor for dementia and Alzheimer’s disease at older ages.
The MIND diet was created in 2015 and is based on the Mediterranean and DASH diets. It aims to improve brain health and cognitive performance by emphasizing the consumption of fruits (mainly berries), green leafy vegetables, nuts, olive oil, whole grains, fish, and beans while limiting the consumption of butter, cheese, red meat, fried foods, and sweets and pastries. MIND diet studies have produced promising results, but the studies have used observational designs and only included older adults.
In this 3-month randomized controlled trial, 37 women (aged 40–60) with obesity were assigned to either a calorie-restricted modified MIND diet or a calorie-restricted control diet. The macronutrient distribution of both diets was 50–55% carbohydrates, 30% fat, and 15–20% protein, and an individualized calorie deficit of −500 kcal/day was set for each participant. The participants met with a registered dietitian each week, and a 3-day food recall was performed to assess dietary adherence. Each meal and snack in the MIND group was scored according to whether it fit the MIND diet criteria. The participants were classified as having successfully adhered to the MIND diet if at least 80% of their meals and snacks were scored as meeting the MIND diet criteria.
The primary outcomes were verbal short memory measured by the Forward Digit Span Task (FDST) and Backward Digit Span Task (BDST), working memory capacity measured by the Letter Number Sequencing Task (LNST), attention and visual scanning measured by the Symbol Digit Modality Task (SDMT), verbal recognition memory measured by the Auditory Verbal Learning Test (AVLT), and executive function and task switching measured by the Trail Making Test A and B.
The secondary outcomes were changes in brain structures measured using magnetic resonance imaging (data from 11 participants in each group were included), anthropometrics, and plasma levels of brain-derived neurotrophic factor (BDNF), amyloid-beta, and homocysteine.
Compared to baseline, there were improvements in all cognitive tests in both groups, which suggests there may have been a learning effect due to more familiarity with the content of the tests the second time around. Nevertheless, compared to the control group, test scores on the FDST, BDST, LNST, SDMT, Trail Making Test A, and AVLT improved to a greater extent in the MIND group.
In the secondary outcomes, body weight and percent body fat decreased to a greater extent in the MIND group compared to the control group. Also, homocysteine levels decreased in the MIND group compared to the control group, and there was a nonsignificant increase in BDNF in the MIND group compared to the control group. There was an increase in the surface area of the inferior frontal gyrus in the MIND group compared to the control group.
The researchers did not adjust for multiple comparisons, despite the inclusion of numerous outcomes, which increases the risk of false-positive results. Due to the smaller sample size for changes in brain structure, these results should be interpreted with extra caution. Because the sample only included middle-aged women, the results may not be generalizable to other populations.
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