June 2019 Issue
Cognitive Health: Foods and Nutrients That Show Promise
By Mindy Hermann, MBA, RDN
Today’s Dietitian
Vol. 21, No. 6, P. 10
Today, the pursuit of health goes beyond striving for a healthy body; it also involves the quest for a healthy mind. Indeed, science suggests that factors linked to physical health, namely diet and physical activity, also are linked to cognitive health.
Cognitive health encompasses normal brain and mental functioning, management of depression and other mood-related disorders, decline in cognition as part of the normal aging process, and impairments such as Alzheimer’s disease and other forms of dementia. Research in this area tends to focus on the impact of food and nutrients on one or two particular aspects of cognitive health rather than on cognitive health as a whole.
One line of thought suggests that inflammation causes damage to the brain. Researchers in Italy recently summarized studies showing a relationship between neuroinflammation and Alzheimer’s disease and discussed the possible role food and nutrition might play in reducing the type of inflammation that causes deterioration in mental functioning.1 And while more supporting research is needed, a recent review article pointed to the anti-inflammatory properties of the ketogenic diet as potentially protecting the brain from Alzheimer’s disease.2 Data from the National Health and Nutrition Examination Survey (NHANES) correlated a higher Dietary Inflammatory Index, a tool for quantitatively assessing the role of diet in contributing to inflammatory markers and chronic disease, with greater risk of depression, an aspect of cognitive health.3
Another area of interest regarding inflammation’s impact on cognition is the gut-brain axis, that is, the biochemical, endocrine, and neurological signaling between the nervous systems of the gastrointestinal tract and the brain. Several factors, including diet, medication, chronic disease, and the composition of the gut microbiota, affect communication along the gut-brain axis. These factors also are thought to impact inflammation. One study inversely correlated the activity of neurotransmitter-producing gut bacteria with brain characteristics associated with depression.4 Animal models of Alzheimer’s and other dementias suggest that gut bacteria synthesize substances that impact cognitive health.5
The foods and nutrients highlighted in this article have been shown to benefit various aspects of cognitive health; however, it’s still unknown whether they reduce inflammation, affect the gut-brain axis, modify the composition of the gut microbiota, or impact the brain in other ways.
Spotlight on Foods for Cognitive Health
• Walnuts and nuts. Several studies suggest a potential relationship between nuts, particularly walnuts, and cognitive health. Walnuts, whose antioxidant activities are well documented, contain vitamin E and unique polyphenols, including the ellagitannin pedunculagin.6 Ellagitannins have antioxidant and anti-inflammatory properties, and their hydrolysis releases a compound that’s activated by gut bacteria. Walnuts also contain more alpha-linolenic acid, an omega-3 fatty acid, than other nuts. Omega-3s are present in high concentrations in the brain, hence the thought that dietary omega-3s play a role in cognitive health.7
In early 2019, a study based on data from NHANES associated walnut consumption with lower depression scores. The research team pooled 24-hour recall data from the 2005–2014 NHANES surveys and derived depression scores from PHQ-9 (Patient Health Questionnaire) self-report responses. They divided the data from more than 26,000 participants into consumers of walnuts, walnuts plus other nuts, other nuts only, or no nuts. Walnut consumers, and women more than men, showed lower depression scores, suggesting that walnuts may play a role in mental health.8
The effects of nuts on cognition may extend beyond walnuts. Chinese adult participants (aged 55 and older) in the China Health and Nutrition Survey who ate an average of at least 10 g nuts, primarily peanuts, per day had higher global cognition scores, as measured through a series of telephone interviews that evaluated thinking, reasoning, and memory.9 They also were less likely to have poor cognitive function.
• Fish and seafood. The relationship between fish and seafood and cognitive health appears promising. Two pooled studies showed that groups eating the most fish had lower risk of depression.10,11 Higher fish intake also has been linked to reduced incidence of Alzheimer’s disease.12 The benefits of fish consumption have been attributed to its omega-3 fatty acid content, but research to date is inconclusive.
• Blueberries. Researchers who conducted a 12-week study on participants who consumed blueberry concentrate (387 mg anthocyanidins/30 mL) vs placebo observed increases in brain activity in areas associated with cognition among those who drank the concentrate.13 The anthocyanins in blueberries are thought to confer antioxidant and anti-inflammatory properties. Blueberries contain an average of 199 mg anthocyanins/100 g blueberries,14 so while matching the amount of anthocyanins in blueberry concentrate is realistic, it requires eating more than a cup of blueberries each day.
• Soy products. A Taiwanese epidemiologic study suggests that daily soy consumption may reduce risk of cognitive decline. A group of 1,105 Taiwanese adults aged 65 and older completed a simple mental status questionnaire (the Short Portable Mental Status Questionnaire) and a food frequency questionnaire. Those eating soy up to once per day were 43% less likely to be cognitively impaired, and those consuming soy daily were 55% less likely to be cognitively impaired.15 Including soy regularly in the diet is both reasonable and doable with products such as tofu, edamame, soymilk, and other common soyfoods and beverages. It’s suggested that the mechanism of action of the soy isoflavones in soyfoods may be related to their hormonelike activities rather than any effects on inflammation.16
• Turmeric (curcumin). The antioxidant and anti-inflammatory properties of curcumin, the active ingredient in turmeric, make it attractive for cognitive health. A 2019 systematic review and meta-analysis of six clinical trials looking at various aspects of cognitive health suggests that curcumin may help improve scores on measures of cognitive function.17 The review of this limited number of studies concludes that curcumin doesn’t appear to impact Alzheimer’s and other forms of dementia. Additional human studies are needed to help determine a possible role.
• MIND diet. The Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet was created to help slow cognitive decline with age and reduce the incidence of Alzheimer’s disease. “The MIND diet combines two heart-healthy diets—DASH and Mediterranean—and optimizes them for brain health,” says Maggie Moon, MS, RD, author of The MIND Diet. “The MIND diet specifically recommends berries and leafy greens, though all fruits and vegetables are an important part of a healthful eating pattern. The diet also includes nuts, olive oil, whole grains, fish, beans, poultry, and wine (no more than one glass per day).” It’s thought that the antioxidants and nutrients these foods deliver in the MIND diet, such as bioactive compounds in vegetables and omega-3 fatty acids in fish, reduce the type of oxidative stress and inflammation that damages brain cells. Butter, margarine, cheese, red meat, fried foods, and sweets should be limited or avoided.
Several recent studies support the beneficial effects of the MIND diet. In a 12-year Australian study comparing the MIND and Mediterranean diets, only the MIND diet was associated with reduced risk of cognitive decline.18 A study of French older adults found an inverse relationship between adherence to the MIND diet and subjective memory complaints in participants aged 70 and older.19 The MIND diet also has been linked to reduced risk of Parkinson’s disease and slower progression in those with the disease.20
“One of the best features about the MIND diet is that it yields results even when followed half way,” Moon says. “That said, the strongest benefits are seen with following it more closely.”
• Mediterranean diet. The Mediterranean diet alone has been shown to have an independent effect on cognition. As part of the PREDIMED study, participants were assigned to follow a Mediterranean diet plus consume 1 L/week of olive oil, a Mediterranean diet plus 30 g/day of mixed nuts, or a control diet. Those on the experimental diet plus olive oil scored better than controls on auditory verbal learning and color trail tests while the nut group improved performance in memory tests.21 As part of the CARDIA study in young adults, both the Mediterranean and the A Priori Diet Quality Score (APDQS) dietary patterns were associated with less midlife decline in verbal memory, processing speed, and executive function.22 (The APDQS involved points tabulated for high intake of healthful foods and low intake of fried foods, salty snacks, sweets, high-fat dairy, and sugar-sweetened soft drinks.) These results suggest that overall diet may be as important as individual components.
• Pomegranate juice. According to Christine Rosenbloom, PhD, RDN, FAND, who monitors research on nutrition and aging for her blog Food and Fitness After 50, pomegranate juice also may have positive effects on cognitive health. “Like walnuts, pomegranate juice is rich in ellagitannins,” she says. “Research presented at the 2019 meeting of the American Association for Geriatric Psychiatry showed that a daily 8-oz serving of pomegranate juice improved visual learning and retention of learning in a year-long, randomized, placebo-controlled, double-blinded study on adults with an average age of 60. It’s thought that pomegranate juice may work through the gut microbiome.”
Best Advice
A healthful diet consistently confers the most consistent effects on cognitive health. Until research more conclusively ties the anti-inflammatory properties of specific foods and nutrients to improved cognition, counseling clients on a diet such as MIND is the best action toward brain and overall health.
— Mindy Hermann, MBA, RDN, is a food and nutrition writer and speaker based in the New York metro area.
References
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