While healthy diets show links to better brain aging, researchers caution against overhyping “brain foods” and argue for combined approaches that target multiple lifestyle factors.
Review: Dietary Patterns and Brain Aging: Enthusiasm Before Evidence? Image Credit: Elena Eryomenko / Shutterstock
In a recent study published in the Annual Review of Nutrition, researchers examined the role of dietary patterns in brain aging and questioned whether current enthusiasm is supported by strong evidence.
The global population is aging at an unprecedented rate. As the population ages, chronic disease prevalence has increased, which mounts a substantial burden on healthcare systems. The World Health Organization (WHO) defines healthy aging as the process of developing and maintaining functional ability that allows well-being in older age. Functional ability includes physical and mental capacities, highlighting the importance of healthy brain aging.
Non-pathological or healthy brain aging leads to non-disabling declines in function, which is distinct from neurodegenerative disorders that occur due to pathological brain aging. Diet quality is one of the determinants of healthy aging, with the public already believing that dietary strategies will delay the onset and decrease the risk of dementia and brain aging.
Consumer surveys in the US suggest that more than half of adults view diet as key to maintaining brain health, although scientific evidence remains mixed. As such, the present study analyzed available evidence on the role of dietary patterns in brain aging, while cautioning that enthusiasm often outpaces the strength of evidence.
Proposed mechanisms of the role of diet in brain aging
Diet quality is deemed a crucial modifiable risk factor for the risk of chronic diseases and promotion of healthy aging. An overall healthy diet is critical in brain development and aging.
Various studies in worms, rodents, and yeasts indicate a role of calorie restriction (CR) and intermittent fasting in health and lifespan. Studies in rodents report that long-term CR could affect the trajectory of brain aging.
While unhealthy dietary patterns can lead to gut dysbiosis, CR and fasting are believed to create favorable effects on the gut microbiota composition. The resultant favorable effects lead to an increased autophagy, ketosis, DNA repair, mitochondrial function, and insulin sensitivity, which reduce microglial inflammation. However, the review stresses that there is little current evidence in humans to support or refute these effects, and most studies are too short or small to draw firm conclusions.
Type 2 diabetes (T2D) and obesity are considered modifiable risk factors for dementia. Data suggest that human obesity, especially in the middle ages, increases dementia risk, although the underlying mechanisms are unknown.
Evidence from animal studies indicates that elevated neuronal senescence and neuroinflammation occur after the consumption of a hypercaloric diet. A central feature of T2D is insulin resistance (IR), with reports suggesting that the brain can also develop IR.
Brain IR can occur in people with dementia, even without concurrent T2D. It presents as an impaired ability to regulate metabolism in peripheral tissues or the brain and could lead to impaired cognition, neurodegeneration, and neuropathology. However, it remains unclear whether T2D and dementia are mechanistically related. Individual food components and nutrients have long been identified with decreased risk of cognitive decline and delay in dementia progression.
Growing evidence suggests that a low vitamin D or K status may have a role in the pathogenesis of Alzheimer’s disease and related dementias (ADRDs). Vitamin D is abundant in fatty fish and fortified foods, while vitamin K is mainly found in green leafy vegetables.
The review emphasizes, however, that evidence for individual nutrients is inconsistent and insufficient for public health recommendations. In line with this, the WHO advises against supplementation with B vitamins, vitamin E, or omega-3 fatty acids for dementia prevention.
Polyphenols are a group of phytochemicals in plant foods, with observational studies linking flavonoid-rich diets to a lower ADRD risk. The mechanisms underlying the beneficial effects of polyphenols include the ability to reduce inflammation, scavenge radicals, and modulate autophagy, cellular signaling, gene expression, neurogenesis, and neuroplasticity. The authors caution that these mechanisms remain largely speculative.
Brain aging, resilience, and dietary patterns
The review highlights the concept of cognitive resilience, the ability to resist, adapt to, or cope with brain pathology, as an important lens through which diet may influence brain aging. A healthy diet may help enhance both resistance to pathology and resilience in its presence.
Evidence from the three most comprehensive global systematic reviews highlights a lower risk of age-related neurodegenerative disease associated with a healthy dietary pattern intake during adulthood. The healthy dietary pattern reflects increased intake of vegetables, fruits, legumes, nuts, unsaturated vegetable oils or fats, fish, and seafood, and lower intake of sugar-sweetened beverages and red and processed meat.
A secondary analysis of the 5-year PREDIMED trial of older adults at high cardiovascular risk found that those following the Mediterranean diet supplemented with nuts or extra virgin olive oil had better cognitive function than controls (who received advice on following a low-fat diet). Moreover, the incidence of mild cognitive impairment was not different between intervention groups, with no cases of dementia observed during the follow-up.
However, a recent randomized controlled trial did not find beneficial effects of the Mediterranean-DASH intervention for the neurodegenerative delay (MIND) diet, with respect to brain volumes or cognitive performance in adults aged ≥65 years with overweight/obesity, a family history of dementia, and no baseline cognitive impairment. This has led to substantial speculation, given the popularity of the MIND diet. It is plausible that this diet might not directly affect brain aging within the three years in the studied population.
Some researchers also noted that dietary improvements in the control group, aimed at weight loss, may have obscured potential effects of the intervention.
The review also highlights broader research limitations, including heterogeneous cognitive tests across studies, reliance on dietary intake measured at a single time point, and difficulties in detecting dietary effects in cognitively healthy populations.
Concluding remarks
Taken together, evidence suggests that any dietary pattern comprising higher intake of vegetables, fish/seafood, nuts, fruits, and unsaturated vegetable oils or fats, and lower intake of sugar-sweetened beverages and processed and red meat is associated with a lower risk of age-related neurodegenerative diseases. However, the biological mechanisms of these protective cognitive effects remain unknown.
The authors emphasize that diet alone is unlikely to achieve clinically meaningful reductions in dementia risk and that multidomain interventions, combining diet with exercise, cognitive training, and cardiovascular risk management, may be more effective.
Emerging metabolomics research may help identify diet-related biomarkers linked to dementia risk, but this field remains in its infancy.