The prevalence of diabetes is rapidly increasing worldwide, largely driven by lifestyle-related factors and obesity. In both diabetic patients and high-fat diet–induced diabetic mouse models, the expression of the glycosyltransferase N-acetylglucosaminyltransferase IVa (GnT-IVa) is markedly reduced in pancreatic β cells. This reduction impairs N-glycosylation of key nutrient transporters, such as glucose transporter 2 (GLUT2) and the cationic amino acid transporter 3 (CAT3), leading to decreased cell surface expression and defective nutrient sensing. Consequently, insulin secretion is compromised, contributing to the development of type 2 diabetes. GnT-IVa promotes the formation of multi-branched N-glycans that interact with extracellular galectins to assemble galectin lattices on the βcell surface. These lattices regulate membrane protein stability and localization, thereby sustaining insulin secretory function. Restoration of GnT-IVa expression in pancreatic β cells prevents high-fat diet–induced diabetes in vivo, illuminating GnT-IVa as a promising therapeutic and preventive target. Furthermore, alterations in N-glycan profiles in diabetic patients suggest their potential as biomarkers. Given the high expression of GnT-IVa in various cancers, elucidation of GnT-IVa-dependent glycosylation mechanisms is expected to have broad implications for metabolic disease and cancer research.