Ultrafiltered Mulberry (Morus alba L.) Leaf Albumin-Type Protein Attenuates High-Fat Diet-Induced Obesity in Mice by Remodeling Gut Microbiota and Metabolic Homeostasis

Obesity is a chronic metabolic disorder closely associated with dyslipidemia, insulin resistance, low-grade inflammation, and gut microbiota dysbiosis. Mulberry leaves are rich in bioactive proteins, but whether mulberry leaf albumin-type protein can improve diet-induced obesity remains unclear. In this study, ultrafiltered mulberry leaf albumin-type protein (UMP) was prepared and its anti-obesity effects were evaluated in high-fat diet (HFD)-fed C57BL/6J mice. UMP contained 87.12 ± 0.52 g/100 g protein, 2.52 ± 0.00 g/100 g polyphenols, and 8.21 ± 1.49 g/100 g polysaccharides, with two major albumin-type protein bands of approximately 14 and 52 kDa. Structural analysis showed that UMP was mainly composed of β-turns and α-helices. In HFD-fed mice, daily administration of UMP for 16 weeks reduced body weight gain by 3.85 g and 5.63 g in the low- and high-dose groups, respectively, without affecting food intake. Biochemical assays, glucose and insulin tolerance tests, and histological analysis showed that UMP improved insulin responsiveness, alleviated serum dyslipidemia, reduced hepatic lipid accumulation, and decreased circulating alanine aminotransferase, aspartate aminotransferase, and lipopolysaccharide levels. Histological analysis and nuclear magnetic resonance-based short-chain fatty acid quantification further showed that UMP protected colonic morphology and increased colonic short-chain fatty acid levels. Gut microbiota analysis showed that UMP restored microbial diversity, reduced the Firmicutes/Bacteroidota ratio, and enriched potentially beneficial genera, including Ileibacterium and norank_f_Muribaculaceae. Fecal biochemical assays suggested that UMP promoted fecal free fatty acid excretion and partially improved bile acid-related metabolic alterations. Untargeted serum metabolomics revealed that UMP reshaped metabolic pathways related to lipid turnover, bile acid signaling, glucose utilization, and glucuronidation. Correlation analysis linked UMP-enriched bacterial taxa with key metabolites involved in fatty acid and energy metabolism. Together, these findings indicate that UMP attenuates HFD-induced obesity through coordinated regulation of gut microbiota, intestinal metabolites, and systemic metabolic homeostasis. UMP may therefore represent a promising functional dietary protein for the prevention of obesity-related metabolic disorders.