Here we find that α-linolenic acid (ALA) and 11,14-eicosadienoic acid (EDA), which are naturally enriched in black rice, inhibit amyloid pathology, rescue cognition and extend lifespan in mouse preclinical models of Alzheimer’s disease via allosteric activation of G protein-coupled receptor 120 (GPR120) in plaque-associated macrophages and activated microglia. This evidence concerns the gene FFAR4 and Alzheimer disease.