The inclusion of nuts in the diet is associated with a decreased risk of coronary artery disease, hypertension, gallstones, diabetes, cancer, metabolic syndrome, and visceral obesity. Frequent consumption of berries seems to be associated with improved cardiovascular and cancer outcomes, improved immune function, and decreased recurrence of urinary tract infections; the consumption of nuts and berries is associated with reduction in oxidative damage, inflammation, vascular reactivity, and platelet aggregation, and improvement in immune functions. However, only recently have the effects of nut and berry consumption on the brain, different neural systems, and cognition been studied. There is growing evidence that the synergy and interaction of all of the nutrients and other bioactive components in nuts and berries can have a beneficial effect on the brain and cognition. Regular nut consumption, berry consumption, or both could possibly be used as an adjunctive therapeutic strategy in the treatment and prevention of several neurodegenerative diseases and age-related brain dysfunction. A number of animal and a growing number of human studies show that moderate-duration dietary supplementation with nuts, berry fruit, or both is capable of altering cognitive performance in humans, perhaps forestalling or reversing the effects of neurodegeneration in aging.
Alex’s Notes: Twenty years ago, nuts and berries were often overlooked and seen as a snack. Recently, however, they have risen to a place of power as superior foods for health, and some advocates even labeled them with the title of “functional food.” Regardless, the data exists supporting their health effects, but only a limited amount of research has focused on the cognitive side of things. Two main components of cognitive decline are poor vascular health, and oxidative stress and inflammation. The review at hand summarizes the recent knowledge on the expanding area of nuts and berries on cognition.
The first study to show the beneficial effects of tree nuts on cognition what published in 2008, and had rats fed diets containing various amounts of ground walnuts with skin. Whereas too many walnuts were impaired memory, the most positive effects were seen with a diet equating one ounce of walnut consumption daily in humans. It was also found that this amount of walnuts reduced levels of toxic proteins in the brain that increase via oxidative stress and inflammation. Almonds have also shown benefits in cognitive impairment as doses equivalent to 5-6 nuts daily.
Human studies seem to support the above, with strong evidence coming from the PREDIMED study. A Mediterranean diet supplemented with 30 grams of mixed nuts (15g walnuts, 7.5g almonds, & 7.5g hazelnuts) improved plasma brain-derived neurotrophic factor (BDNF), specifically in persons with depression, a common side-effect of Alzheimer’s disease. BDNF supports the survival of existing neurons and encourages the growth and differentiation of new neurons.
As for berries, the first study showing benefits of consumption showed a 1.5% diet of blueberries or strawberries improved working memory. It was later shown that the beneficial polyphenol compounds cross the blood-brain barrier to enter the brain, and thus it appears that once consumed, dietary polyphenols from berries are both neuroavailable and localize in various brain regions that are important for learning and memory. Another study demonstrated that a 2% blackcurrant or cranberry diet enhanced neuronal signaling, and that a 2% blueberry diet reduced cognitive impairments by means suggestive of increased muscle tone and control.
Very small-scale preliminary human studies show promising support for berries as well. 12 weeks of daily supplementation of 6-9 mL blueberry juice per kilogram of bodyweight among nine older adults improved cognitive function, and a recent epidemiologic study showed that greater intakes of blueberries and strawberries were associated with slower rates of cognitive decline in over 16,000 women over 70 years of age. The authors of the latter study concluded that berry consumption could delay cognitive aging by up to 2.5 years.
Overall, animal studies demonstrate that different neural systems and cognition can be affected by short- and long-term consumption of nuts and berries, and human trials suggests potential positive effects, especially among the elderly, depress, or memory impaired.