Plant-predominant dietary patterns (DPs) such as the Mediterranean diet (MD) have emerged as promising modifiable strategies for healthy cognitive ageing (1). However, evidence across different plant-predominant DPs remains mixed and has not been comprehensively synthesised. Women also experience a higher risk of dementia and distinct cognitive trajectories, yet sex-specific evidence remains limited (2). Therefore, this review aimed to synthesise evidence on the prospective associations between plant-predominant DPs, including MD, Dietary Approaches to Stop Hypertension (DASH), Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND), plant-based diet indices (PDIs), country/regional guidelines (e.g. Nordic DP, EAT-Lancet diet), and data-driven patterns, with cognitive outcomes in mixed-sex and women-only populations aged ≥ 45 years. MEDLINE, EMBASE, CINAHL and PsycINFO were searched from inception through May 2, 2026, following PRISMA guidelines. Data were extracted on population characteristics, dietary assessment, cognitive outcome, effect estimates and covariates. Risk of bias was assessed using the Newcastle-Ottawa Scale. Quality-effects meta-analyses were conducted for DPs with ≥ 2 eligible studies, stratified by global cognitive decline and global cognitive performance. Effect sizes (ESs) with 95% confidence intervals (CIs) were calculated separately by dietary pattern, cognitive outcome, and analytical approach. Between-study heterogeneity was assessed using I2, and sensitivity analyses were conducted using leave-one-out approaches. Fifty-four studies representing 37 cohorts were included, with 30 contributing to meta-analyses. Greater MD adherence was significantly associated with slower global cognitive decline (n = 13, ES = 0.02, 95% CI: 0.00, 0.04, I2 = 67%) and better cognitive performance at follow-up (n = 2, ES = 0.14, 95% CI: 0.1, 0.17, I2 = 11%). MIND and DASH diets showed favourable, non-significant associations. Healthful PDI, emphasising whole and minimally processed plant foods, was significantly associated with better outcomes (n = 2, ES = 0.02, 95% CI: 0.00, 0.04, I2 = 0%), while unhealthful PDI, characterised by refined and processed plant foods, was associated with worse outcomes (n = 2, ES = -0.01, 95% CI: -0.03, 0.00, I2 = 0%), suggesting quality of plant foods may influence cognition. Stronger associations were observed in populations with higher baseline vascular or cerebrovascular risk. Sex-stratified analyses across several patterns showed more pronounced effects in women; however, findings were inconsistent, likely due to the limited number of sex-stratified studies available. Overall, substantial heterogeneity appeared to be influenced by population characteristics and methodological differences. In conclusion, higher adherence to high-quality plant-predominant DPs, particularly the MD, may support healthy cognitive ageing although effect sizes are small and heterogeneity is substantial. Findings highlight the importance of plant-food quality, sex and population health context in understanding the diet-cognition relationship. More long-term prospective studies with standardised dietary and cognitive assessments are needed to inform targeted dietary recommendations for dementia prevention.