Systematic review and meta-analysis of randomised controlled trials examining phytochemical-rich foods (polyphenols, anthocyanins, flavanols, carotenoids) and cognitive function in adults aged 50+. Covers five cognitive domains: global cognition, episodic memory, executive function, attention/processing speed, and working memory. Findings show small, consistent cognitive benefits, strongest for global cognition and episodic memory, with effects concentrated in cognitively vulnerable subgroups (APOE-ε4 carriers, baseline decliners, cardiometabolic risk). PRISMA 2020 and Cochrane RoB 2 compliant. PROSPERO registered.