Edible Marine Red Alga Gracilaria coronopifolia as a Potential Functional Ingredient: Chemical Profiling and Metabolic Effects in Diet-Induced Obese Rats

Marine macroalgae are increasingly recognized as sources of bioactive compounds with potential benefits for metabolic health. This study investigated the chemical composition and metabolic effects of a 70% ethanol extract of the edible red alga Gracilaria coronopifolia in a high-fat diet (HFD)-induced obesity model in rats. Chemical profiling using liquid chromatography–high-resolution mass spectrometry (LC–HRMS) identified several classes of metabolites, including sterols, phenolic acids, flavonoids, and fatty acid derivatives such as palmitoleic acid, chlorogenic acid, gallic acid, and quercetin. Male Wistar rats were fed an HFD for 11 weeks to induce obesity and subsequently treated with G. coronopifolia extract (40–160 mg/kg body weight) for 28 days, with semaglutide (70 µg/kg) used as a pharmacological comparator. Supplementation with the extract significantly reduced obesity-related parameters compared with untreated HFD controls. The highest extract dose (160 mg/kg) decreased final body weight from 294.8 ± 43.3 g in HFD rats to 215.2 ± 11.9 g, reduced visceral fat mass from 22.7 ± 2.37 g to 7.63 ± 1.19 g, and lowered the adiposity index from 6.39 ± 0.45% to 3.31 ± 0.22%. The extract also improved serum lipid profiles, reducing triglyceride levels from 185.46 ± 11.58 mg/dL in the HFD group to 101.54 ± 24.29 mg/dL, while increasing HDL concentrations to 75.64 ± 4.73 mg/dL. In addition, treatment increased adiponectin levels (to 779.55 ± 15.66) and decreased leptin (4.94 ± 0.75) and amylin (532.44 ± 30.00) relative to obese controls. Histological analysis demonstrated a reduction in adipocyte hypertrophy. Gene expression analysis revealed downregulation of hypothalamic Npy and adipose Fas and Pparγ, together with upregulation of Pomc, Mc4r, and Cpt1. These findings suggest that G. coronopifolia extract improves metabolic disturbances associated with diet-induced obesity through coordinated regulation of appetite signaling and lipid metabolism, supporting its potential development as a marine-derived functional food ingredient.