Marine-Derived Aqueous Extracts from Edible Ulva fasciata and Ulva rigida Modulate Fructose-Induced Metabolic Dysfunction, Adipose Redox Imbalance and Fecal Metabolite Shifts in Rats

Edible green seaweeds are increasingly investigated as sources of bioactive ingredients relevant to diet-related metabolic dysfunction. This study evaluated aqueous extracts of Ulva fasciata and Ulva rigida at 150 and 300 mg/kg in a fructose–saccharin-associated rat model. Rats were exposed to 10% fructose plus 0.03% saccharin in drinking water for 8 weeks. Thereafter, fructose–saccharin exposure was discontinued, and the respective treatment groups received orlistat or low- and high-dose U. fasciata or U. rigida extracts for 4 weeks. Body weight, adiposity, oral glucose tolerance, serum biochemical and insulin-related indices, adipose redox status, and fecal metabolites and extract composition were assessed. Fructose exposure was associated with greater adiposity, impaired glucose tolerance, elevated serum insulin, HOMA-IR, circulating lipids and other biochemical markers, increased adipose lipid peroxidation, and reduced antioxidant defense. Both Ulva extracts were associated with attenuation of these alterations, with high-dose U. fasciata showing the most consistent response. GC-MS revealed treatment-associated differences in fecal metabolites, while extract characterization demonstrated substantial carbohydrate and sulphate contents, functional groups consistent with carbohydrate- and sulphate-associated structures, and diverse putatively annotated carbohydrate-, phenolic- and lipid-related LC-MS features. Overall, both Ulva species were associated with improved metabolic and adipose redox profiles alongside modulation of fecal metabolite patterns.