Given the vast number of people in the United States who are approaching 65 years of age, there is a need for interdisciplinary research on factors influencing the trajectory of cognition and brain aging in older adults. In a recent review published in Nutrients, researchers examine the collective effect of diet and exercise interventions on age-related cognition and brain health changes.
Study: Impact of Diet and Exercise Interventions on Cognition and Brain Health in Older Adults: A Narrative Review. Image Credit: Isarat / Shutterstock.com
Age-related cognitive decline
Reduced processing speed is one of the major cognitive deficits observed in older adults, in addition to impaired semantic and episodic memory. Likewise, working memory that actively maintains information in the short term to enable goal-directed decision-making also declines because of aging.
Reduced working memory results in a corresponding reduction in executive functions in advanced age. Due to structural and functional changes in the brain, aging also affects an individual's crystallized and fluid intelligence.
Structural changes in the brain associated with aging include reduced gray matter volume and cortical thickness. Gray matter volume, a measure of neuronal and glial cell bodies, declines in volume within multiple brain regions, including the medial temporal lobe of the hippocampus and entorhinal cortex during aging. Specifically, age-related reduction of hippocampal volume, resulting from neuronal cell loss and a decrease in neurogenesis, is associated with decreased cognitive performance on memory, spatial learning, and emotional regulation tasks.
Effect of diet and exercise on aging
It is crucial to understand the relationship between nutrient consumption and neuronal function, neurometabolic processes, and cognitive decline.
There is growing evidence that nutrients from various foods across multiple food groups have synergistic effects beyond the effects of individual nutrients. For example, the absorption of vitamins from green salad improves when served with olive oil and vinegar rather than a fat-free ranch dressing.
To date, the Mediterranean diet (MeDi), Dietary Approaches to Stop Hypertension (DASH), and Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diets are most frequently referenced in the literature. Each of these diets appears to improve neurological signs of aging, including cell membrane and vascular integrity, inflammation, resolution, and oxidation, as well as lipid and glucose metabolism.
Considerable evidence suggests that the MeDi and MIND diets are associated with both general and domain-specific facets of cognitive ability. For example, several studies have associated the MeDi diet with attention and long-term memory. Likewise, adherence to the MIND diet is positively associated with visuospatial ability, perceptual speed, and executive function.
The impact of the ketogenic diet (KD) and intermittent fasting (IF) on cognition and brain function have also been widely studied, as weight management diets appear to improve cognitive functioning. Likewise, weight loss achieved through bariatric surgery enhances attention, memory, and executive function.
In addition to diet, exercise positively affects cognition, as demonstrated by a previous study in which overweight and obese adults were enrolled in a one-year behavioral weight loss intervention. These patients were on an energy-restricted diet, an energy-restricted diet with 150 minutes of moderate-intensity exercise every week, or an energy-restricted diet with 250 minutes of exercise every week.
Post-intervention, weight markedly decreased across both groups. More specifically, the high-exercise group improved their performance on Iowa Gambling Task (IGT) reward relative to the other two study groups. Overall, more exercise with behavioral weight loss regimens had an additional benefit on executive functioning, even with no weight loss benefits.
Endurance exercise typically encompasses walking, jogging, running, swimming, and cycling, with walking being the most practiced form among older adults. Higher endurance fitness levels are associated with less age-related brain volume decline.
Randomized controlled trials examining the role of endurance exercise on cognition have led to mixed results. However, all evidence suggests that endurance exercise in older adults improved cognitive performance, visual attention, and memory, promoted brain plasticity, and weakened hippocampal atrophy.
Similarly, a recent systematic review found that resistance training positively affected older adults' executive and global cognitive functions. This form of exercise also positively impacted memory, albeit weakly, and did not significantly improve attention. Additionally, tri-weekly, as compared to biweekly resistance training, positively affected general cognitive abilities.
No evidence of an interference effect of aerobic and resistance training has been reported. However, literature comparing resistance or combined exercise to a non-exercise control is limited. Thus, it remains unclear which exercises should be prescribed to maintain and enhance cognition and brain health among older adults.
Behavioral interventions like yoga appear to mitigate age-related and neurodegenerative decline. In one review examining the effects of practicing yoga on brain structures, function, and cerebral blood flow, yoga positively affected the structure and function of the hippocampus, prefrontal and cingulate cortex, amygdala, and neuronal networks.
A recent literature review evaluating the effect of tai chi, a traditional Chinese martial art, on brain structure and neurobehavior changes found that this form of exercise also increased cortical grey matter volume, improved neural activity and homogeneity, and increased neural connectivity in the frontal, temporal, and occipital lobes, cerebellum, and thalamus.
All diets evaluated in this review addressed factors associated with aging and neurodegenerative diseases like Alzheimer's disease and related dementias (ADRD). Depending on the type and intensity, exercises were found to positively affect brain vascularization, neurotransmitter regulation, growth factors, and neurogenesis.
- Key, M. N., & Szabo-Reed, A. N. (2023). Impact of Diet and Exercise Interventions on Cognition and Brain Health in Older Adults: A Narrative Review. Nutrients 15(11);2495. doi:10.3390/nu15112495