Unhealthy nutrition, such as that characterized by a westernized style, can lead to metabolic syndrome (MetS), a cluster of cardio-metabolic risk factors associated with increased incidence of cognitive dysfunction, reducing the quality of life during aging. By contrast, regular consumption of nutraceuticals may promote brain and metabolic health, with limited side effects. We investigated whether oral administration of the polyphenol rosmarinic acid (RA, 500mg/kg) might protect aged male and female C57BL/6N mice from cognitive decline and metabolic derangement upon western diet (WD, 5.28 kcal/g) feeding, modelling a MetS-like-phenotype. A thorough characterization of both the metabolic and the cognitive/emotional profile was carried-out as well as the analysis of hippocampal gene expression changes, identified through RNAseq. In males, WD resulted in a MetS-like-phenotype as revealed by HOMA-IR, while females showed a generalized increase in emotionality. Administration with RA was able to protect subjects from WD-dependent cognitive dysfunction, as assessed in a spatial memory task. RNAseq analysis indicated that RA might mediate its effects through the modulation of sex hormones signaling cascades in females (Lhb and Lhcgr, mediating anxiolytic-like and cognitive-enhancing effects) while holding metabolic protective properties in both sexes (Glp1r, associated to healthspan-promoting effects). Glp1r is a very promising target as its synthetic agonists have been recently used to prevent metabolic derangements in ageing, thus underlying the mechanism of action of currently known nutraceuticals. H2020 “Ageing with Elegans” [N. 633589].