Does the MIND diet improve cognition in older adults? Original paper

In this randomized controlled trial in older adults, a MIND diet intervention with mild caloric restriction had similar effects on cognition as mild caloric restriction alone.

The effect of the MIND diet on cognition in older adults.

The primary outcome was the change in global cognition score, based on performance on 12 tests. The secondary outcomes were changes in 4 cognitive domain scores (episodic memory, semantic memory, executive function, and perceptual speed) and brain characteristics, measured using magnetic resonance imaging.

604 older adults (at least 65 years old) with overweight or obesity who had lower-than-recommended adherence to the MIND diet and a family history of dementia but did not have mild cognitive impairment.

In this 3-year randomized controlled trial, the participants were assigned to consume the MIND diet with mild caloric restriction or their usual diet with mild caloric restriction (the control). The prescribed daily energy deficit in both groups was 250 kcal. The MIND diet group received a monthly supply of blueberries, mixed nuts, and extra virgin olive oil, while the control group received monthly gift cards.

All of the participants received dietary counseling from a registered dietitian throughout the study. Dietary adherence was monitored throughout the trial using several measures, including body weight, the MIND-diet questionnaire, a food frequency questionnaire, and serum biomarkers of key dietary components (i.e., lutein, zeaxanthin, and alpha-carotene and beta-carotene).

Compared to baseline, global cognition improved in both groups, with no obvious difference between groups. There were also no clear differences between groups for changes in the 4 cognitive domain scores and brain characteristics. White-matter hyperintense lesion volume increased in both groups, whereas hippocampal and total gray-matter and white-matter volumes decreased in both groups.

The MIND diet is a hybrid of the Mediterranean diet and the Dietary Approaches to Stop Hypertension Diet (DASH). Observational evidence indicates that higher adherence to the MIND diet is associated with slower cognitive decline and a reduced risk of dementia.^[1][2] The MIND diet incorporates many, though not all, of the characteristics of the Mediterranean and DASH diets while also placing a greater emphasis on the consumption of green leafy vegetables, nuts, berries, and olive oil. Additionally, the diet is designed to minimize the intake of foods rich in saturated fat and sugar, such as red or processed meat, butter and margarine, whole-fat cheese, pastries and sweets, and fried foods.

The composition of the MIND diet is the result of evidence from animal studies, as well as observational studies in humans that found an association between the consumption of certain nutrients and/or foods and the risk of dementia and the rate of cognitive decline. Because the overarching goal of the MIND diet is to promote brain health and preserve cognition with aging, it differs in some notable ways from the Mediterranean and DASH diets, as the Mediterranean diet is often promoted for improving overall health and preventing heart disease, and the DASH diet is most commonly prescribed for reducing blood pressure.

A shared feature of the Mediterranean and DASH diets is a high consumption of fruit in general, a principle not shared by the MIND diet. The MIND diet includes a high consumption of berries, specifically because observational studies have tended to find no association between total fruit intake and cognitive-protective effects,^[3][4][5] whereas a higher consumption of berries has been associated with a slower rate of cognitive decline.^[6] Berries may be uniquely good for brain health due to their abundant content of flavonoids, most notably anthocyanins, which have shown antioxidant and anti-inflammatory properties in animal experiments.^[7]

Similarly, although the MIND diet, like the Mediterranean and DASH diets, recommends a high total vegetable intake, it differs in that it highlights green leafy vegetables because they have been identified in some studies as having particularly strong cognitive-protective effects.^[8][4][5] This effect may be primarily attributed to their rich content of carotenoids (e.g., lutein and zeaxanthin) and vitamin K, higher intakes of which have been associated with a reduced risk of dementia and cognitive decline.^[9][10]

Green leafy vegetables are also a decent source of vitamin E, and higher intakes of vitamin E have consistently been associated with a reduced risk of dementia and cognitive decline.^[11] Nuts are one of the best sources of vitamin E. They are also generally rich in unsaturated fat and contain low amounts of saturated fat. Several studies have reported associations between higher intakes of saturated fat with increased rates of cognitive decline and higher intakes of unsaturated fat rate with reduced rates of cognitive decline.^[12] Olive oil is another component with a satisfactory unsaturated fat to saturated fat ratio, and one study found that a Mediterranean diet supplemented with extra virgin olive oil or nuts might result in better global cognition than a low-fat diet.^[13]

Among unsaturated fatty acids, omega-3 fatty acids, especially docosahexaenoic acid (DHA), seems to be particularly important. DHA is the primary fat found in the brain and is of vital importance for neuronal membranes.^[14] Animal studies have indicated that diets enriched in omega-3 fatty acids promote superior learning acquisition and memory performance.^[11] Fatty fish is rich in omega-3 fatty acids, which is why it’s one of few animal-based foods included in the MIND diet. However, only one fish meal per week is recommended because observational studies have typically not reported greater cognitive-protective effects with higher intakes.^[11] This is another way in which the MIND diet differs from the Mediterranean and DASH diets, which promote a higher weekly intake of fish.

A third way the MIND diet differs from the Mediterranean and DASH diets is that the latter emphasize the consumption of about 2 servings of reduced-fat dairy products per day.^[15][16] Due to a lack of evidence from observational studies indicating a beneficial association between dairy product consumption and the risk of dementia and cognitive decline,^[17] dairy products are not emphasized in the MIND diet. Furthermore, the consumption of high-fat dairy products is discouraged due to their high saturated fat content.

Although the available mechanistic and observational evidence strongly suggests that the MIND diet would have cognitive-protective effects, the results of the summarized study indicated that the MIND diet was no better than the participants’ usual diet. This doesn’t necessarily mean that the MIND diet is ineffective for improving cognitive outcomes, as it ultimately comes down to what type of diet the MIND diet is being compared to, and notably, there was an improvement in global cognition in both groups.

The MIND-diet score was a little over 11 points in the MIND diet group and about 8.5 points in the control group. For reference, the highest possible score, indicating maximal adherence to the MIND diet, is 14. With only a 2.5-point difference in MIND-diet scores between groups, it’s possible that the composition of the diets was too similar for statistically significant differences in cognition to manifest, at least over the limited 3-year intervention period.

MIND diet component servings and scoring

Adapted from Morris et al., 2015, Alzheimer’s Dement.

One other randomized controlled trial has evaluated the effect of the MIND diet on cognition.^[18] In this 3-month study, 37 women with obesity (average age of 48) consumed either a calorie-restricted MIND diet or a calorie-restricted standard diet (the participants received information about healthy food choices). In contrast to the summarized study, performance on several cognitive tests improved in the MIND diet group compared to the control group. Interestingly, weight loss was greater in the MIND diet group than the control group, whereas in the summarized study, which also included participants with obesity, weight loss was the same between groups (–5 kg and –4.8 kg in the MIND diet and control diet groups, respectively).

A meta-analysis of longitudinal studies and randomized controlled trials in participants with overweight or obesity reported that weight loss was associated with improvements in several measures of cognitive function.^[19] Thus, another potential reason why there was no difference between the MIND diet and the control diet in the summarized study is that the potential cognitive benefits derived from the foods emphasized in the MIND diet are vastly overshadowed by caloric restriction and significant weight loss, at least in people with overweight or obesity. Consequently, because weight loss was similar between groups, improvements in global cognition were also similar.

In sum, robust evidence from mechanistic and observational studies indicates that the MIND diet has the potential to slow cognitive decline and reduce the risk of dementia. However, the summarized study failed to find any significant benefit compared to the participants’ usual diets. This may be because both diets facilitated significant weight loss, which alone has been shown to improve cognitive function in people with obesity. It could also be due to the participants’ usual diets being too similar to the MIND diet and/or because the intervention period was too short for significant differences in cognitive function to manifest between groups. Another explanation has to do with differences in study design. Because there is a lack of randomized controlled trials on the topic, it’s possible that the MIND diet really isn’t all that effective for improving cognitive outcomes, and the beneficial associations reported in observational studies are just the consequence of bias, confounding and other limitations of this type of research. Ultimately, further randomized controlled trials with a longer intervention duration are needed to determine whether the MIND diet improves cognitive outcomes in older adults.

The planned 50% participation for MRI brain scans was not attained. Only 44% of participants agreed to undergo brain imaging. Thus, there may have been insufficient statistical power to detect significant differences between groups, although the brain-imaging outcomes were very similar between groups.