We investigated the potential metabolic benefits of fish oil (FO) or vegetable argan oil (AO) intake in a dietary model of obesity-linked insulin resistance. Rats were fed a standard chow diet (controls), a high-fat/high-sucrose (HFHS) diet, or an HFHS diet in which 6% of the fat was replaced by either FO or AO feeding, respectively. The HFHS diet increased adipose tissue weight and insulin resistance as revealed by increased fasting glucose and exaggerated glycemic and insulin responses to a glucose tolerance test (intraperitoneal glucose tolerance test). Fish oil feeding prevented fat accretion, reduced fasting glycemia, and normalized glycemic or insulin responses to intraperitoneal glucose tolerance test as compared with HFHS diet. Unlike FO consumption, AO intake failed to prevent obesity, yet restored fasting glycemia back to chow-fed control values. Insulin-induced phosphorylation of Akt and Erk in adipose tissues, skeletal muscles, and liver was greatly attenuated in HFHS rats as compared with chow-fed controls. High-fat/high-sucrose diet-induced insulin resistance was also confirmed in isolated hepatocytes. Fish oil intake prevented insulin resistance by improving or fully restoring insulin signaling responses in all tissues and isolated hepatocytes. Argan oil intake also improved insulin-dependent phosphorylations of Akt and Erk; and in adipose tissue, these responses were increased even beyond values observed in chow-fed controls. Taken together, these results strongly support the beneficial action of FO on diet-induced insulin resistance and glucose intolerance, an effect likely explained by the ability of FO to prevent HFHS-induced adiposity. Our data also show for the first time that AO can improve some of the metabolic and insulin signaling abnormalities associated with HFHS feeding.