Plant-derived phenolic metabolites structurally related to phytohormone signaling molecules have gained interest for their potential to modulate oxidative stress and inflammation associated with metabolic disorders. Rosmarinus officinalis (rosemary) and Olea europaea (olive) leaves contain bioactive compounds such as rosmarinic acid and oleuropein, which are involved in plant defense and signaling pathways and may influence inflammatory processes in mammals. This study aimed to investigate the in vivo antioxidant and anti-inflammatory effects of these metabolites. Methanolic extracts of R. officinalis and O. europaea leaves were prepared and administered orally to adult male Wistar rats (8–10 weeks, 200–250 g; n = 6 per group) at 200 mg/kg/day for 28 days. Rats were assigned to control, high-fat diet (HFD), and HFD + plant extract groups. Extracts were characterized by HPLC, confirming rosmarinic acid (12.5 mg/g extract) and oleuropein (8.3 mg/g extract). Serum lipid profiles, hepatic oxidative markers (MDA, SOD, CAT), and inflammatory cytokines (TNF-α, IL-6) were quantified. Treatment with R. officinalis and O. europaea extracts significantly reduced serum triglycerides (−28%) and total cholesterol (−31%) compared with HFD rats. Hepatic MDA decreased by 36%, while SOD and CAT activities increased by 41% and 38%, respectively.NF-α and IL-6 levels were markedly downregulated, indicating attenuation of metabolic inflammation. These results demonstrate that phenolic metabolites structurally related to phytohormone signaling molecules exert potent antioxidant and anti-inflammatory effects in vivo, highlighting their potential as natural modulators of metabolic inflammation and contributors to metabolic homeostasis.