Research Progress on Polyphenols and Polysaccharides from Marine Seaweeds: Promising Diabetes Management Natural Products

Type 2 diabetes mellitus (T2DM) is a major global health burden characterized by insulin resistance, progressive pancreatic β-cell dysfunction, and chronic metabolic dysregulation. Marine seaweeds have emerged as a valuable source of bioactive natural products, particularly polyphenols and polysaccharides, with promising potential for diabetes management. This review focuses on three major contributions: first, the structural diversity of seaweed-derived polyphenols and polysaccharides; second, their multi-target mechanisms of glucose regulation; and third, the structure–activity relationships governing their bioactivities. Current evidence shows that these compounds may help manage type 2 diabetes in several ways, including inhibition of α-amylase and α-glucosidase, attenuation of oxidative stress and chronic inflammation, enhancement of insulin secretion and insulin sensitivity, regulation of lipid metabolism, and modulation of gut microbiota. Key structural determinants such as degree of polymerization, hydroxyl group density, sulfation level, molecular weight, and chemical modifications are discussed in relation to their functional properties. By linking chemical structure with biological function, these findings highlight marine seaweeds as a rich reservoir of multi-target therapeutic candidates for T2DM management and provide a scientific basis for their development as functional food ingredients or lead compounds for novel diabetes management drugs.