Cognitive decline and dementia are major public health challenges, with the global prevalence of dementia projected to increase substantially with population ageing. Diet is increasingly recognised as a key modifiable lifestyle risk factor and an important target for dementia prevention, with research shifting from individual nutrients towards whole dietary patterns that capture potential interactions and synergistic effects between foods and nutrients. Mediterranean, Dietary Approaches to Stop Hypertension (DASH), and Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) dietary patterns have shown promising associations with cognitive health in observational studies (1). However, systematic evidence from randomised controlled trials (RCTs) remains limited. This systematic review aimed to synthesise evidence from RCTs evaluating the effects of dietary patterns on cognition and dementia-related outcomes in older adults. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A comprehensive systematic search was conducted across the Cochrane Central Register of Controlled Trials (CENTRAL), Cumulative Index to Nursing and Allied Health Literature (CINAHL), Embase, Medical Literature Analysis and Retrieval System Online (MEDLINE), Psychological Information Database (PsycINFO), and Scopus. Eligible studies were RCTs investigating the effects of dietary pattern interventions on cognitive outcomes in adults aged ≥65 years. Studies were screened against predefined eligibility criteria, and relevant data on participant characteristics, dietary interventions and cognitive outcomes were extracted. Methodological quality and potential risk of bias were assessed using the Cochrane Risk of Bias 2 (RoB 2) tool. Findings were synthesised according to dietary intervention and cognitive outcome domains. Eighteen publications from RCTs conducted across 15 countries were included. Sample sizes ranged from 23 to 1606 participants, with intervention durations ranging from 4 weeks to approximately 8 years. Dietary interventions included Mediterranean-style diets including those supplemented with extra virgin olive oil or mixed nuts, Mediterranean-ketogenic diet, and NU-AGE diet, MIND diet, Finnish/ Nordic dietary recommendations, high-energy/ high-protein/ low-fat/ low-glycaemic-index nutrition therapy, with several studies incorporating diet within multidomain lifestyle interventions. Global cognition, executive function, memory and processing speed were the most frequently assessed outcomes. Mediterranean-style dietary interventions demonstrated the most consistent improvements, particularly in memory, executive function and global cognition. The multidomain FINGER trial also improved overall cognitive performance compared with usual care. In contrast, several studies, including the MIND and NU-AGE trials only reported improvements in dietary quality or cardiometabolic biomarkers without significant between-group cognitive benefits. Considerable heterogeneity was observed across interventions, cognitive assessments and intervention durations. Mediterranean-style dietary patterns and multidomain lifestyle interventions show the greatest potential to support domain-specific cognitive outcomes in older adults. Larger, adequately powered RCTs with longer follow-up, standardised cognitive assessments and objective measures of dietary adherence are needed to inform the long-term role of dietary patterns in dementia prevention.