Plant-based diets, cognitive function, and Alzheimer's disease

Background: Alzheimer's disease (AD) represents 60-70% of global dementia cases, with up to 45% attributed to modifiable risk factors. Plant-based diets (PBDs) are increasingly recognised for their potential benefits on the gut microbiome, cardiometabolic risk factors and prevention of neurodegenerative disorders. This narrative review synthesises PBDs association with cognitive decline and AD risk. Methods: This review aims to summarise evidence from observational and interventional studies examining vegan, vegetarian, pesco-vegetarian, semi-vegetarian dietary patterns, and PBD indices in relation to cognitive function, incident dementia, AD biomarkers, and neuroimaging outcomes. Results: Long-term observational studies suggest greater adherence to vegan, vegetarian and healthy PBD indexs are associated with lower risk of cognitive decline and dementia, while higher intake of red and processed meat is linked to increased risk. Pesco-vegetarian dietary patterns and higher fish intake appear to confer benefits in memory tests and reduced risk of all-cause dementia, although research is limited. Mechanistically, PBDs are rich in unsaturated fats, fibre, polyphenols and low in saturated fats, which contribute to improving lipid profiles, glycaemic control, endothelial function, and favourable gut-derived metabolites, thereby reducing cardiometabolic burden that is known to accelerate early-stage AD pathophysiology. However, nutritional considerations, including potential deficiencies in vitamin B₁₂ and long-chain omega-3 fatty acids, require consideration when following a PBD. Conclusions: Current evidence suggests PBDs may support cognitive health and reduce the risk of dementia including AD through vascular and metabolic pathways, though long-term interventional studies incorporating biomarkers and neuroimaging are needed to clarify effects and optimise dietary recommendations for AD prevention.