Aqueous extract of small black bean (Rhynchosia nulubilis) improves metabolic dysfunction and hepatic steatosis in diet-induced obese mice

Rhynchosia nulubilis (RN), a traditional black soybean widely consumed in East Asia, is recognized as a protein-rich dietary resource with potential health benefits. However, its role in metabolic dysfunction remains unclear. This study evaluated the effects of an aqueous RN extract in high-fat diet (HFD)-induced obese mice and explored associated metabolic changes using hepatic metabolomics. RN supplementation significantly decreased serum lipid profiles, such as TG by 54.9% in RN 200 mg/kg treatment, insulin resistance, liver injury markers such as AST and ALT by 24.2% and 37.5% in RN 200 mg/kg treatment, hepatic triglyceride accumulation, and NAFLD activity scores by 45.8% RN 200 mg/kg treatment compared with HFD controls. RN treatment was associated with activation of AMP-activated protein kinase (AMPK) and suppression of sterol regulatory element-binding protein-1c (SREBP-1c) and nuclear factor-κB (NF-κB) pathways, along with reduced expression of MCP1 and Il-1β as pro-inflammatory mediators. Metabolomic analysis revealed partial restoration of HFD-induced metabolic disturbances, particularly in bile acid and aromatic amino acid metabolism. These findings suggest that RN may effect improvements in metabolic dysfunction and hepatic steatosis through modulation of lipid metabolism and inflammatory responses, supporting its potential as a functional dietary resource for metabolic health.