Plant-based diet adherence associated with lower cognitive impairment risk in meta-analysis

BACKGROUND: Evidence remains inconclusive regarding plant-based diets preventing cognitive impairment and dementia, as certain plant-based foods, including refined carbohydrates, sweets, sugar-sweetened beverages, and trans fats, may increase dementia risk. OBJECTIVES: To quantitatively synthesize prospective cohort studies on associations between adherence to plant-based diets and the risks of cognitive impairment and dementia. DESIGN: Systematic review and meta-analysis. This study adhered to the PRISMA guidelines and was registered on PROSPERO (No: CRD42024501334). SETTING: Studies published until December 2025 were systematically identified using AgeLine, CINAHL, Embase, MEDLINE, PsycINFO, Scopus, and Web of Science. PARTICIPANTS: The study population comprised adults aged ≥ 20 years with no cognitive impairment at baseline. INTERVENTION: Studies were enrolled if the participants (1) assessed dietary patterns characterized by higher plant-based food consumption and decreased or ceased consumption of animal-based foods or (2) used established dietary indices, including overall plant-based diet index (PDI), healthful plant-based diet index (hPDI), and unhealthful plant-based diet index (uPDI). MEASUREMENTS: Data extraction, risk of bias assessment, and the GRADE approach for assessing certainty of evidence were performed independently by three reviewers. A random-effects model with restricted maximum likelihood was used to calculate pooled risk ratios and 95% confidence intervals. The dose-response meta-analysis used two-stage dose-response regression. RESULTS: The meta-analysis based on seven studies (number of participants: 221,380; number of cases of incident cognitive impairment and dementia: 5668) indicated that participants with greater adherence to plant-based diets had significantly lower risks of cognitive impairment and dementia (pooled risk ratio, 0.74; 95% confidence interval, 0.56-0.97; I = 92.3%) than those with lower adherence. Dose-response relationships modeled using restricted cubic splines indicated that overall PDI and hPDI were negatively associated with risks of cognitive impairment and dementia, whereas uPDI was significantly positively associated with these risks. CONCLUSIONS: This meta-analysis suggests that adherence to plant-based diets, particularly those rich in healthful plant foods, may be associated with a lower risk of cognitive impairment and dementia. However, given the residual heterogeneity and the inherent limitations of observational study designs, large randomised controlled trials are warranted to establish causality.