Brown Seaweeds and Their Bioactive Compounds in Type 2 Diabetes: Mechanisms Underlying Metabolic Regulation

Type 2 diabetes (T2D) is a multifactorial metabolic disorder characterized by chronic hyperglycemia, insulin resistance, and progressive β-cell dysfunction. Chronic hyperglycemia in T2D causes multi-organ and systemic damage, leading to a wide range of complications, including cardiovascular disease and metabolic dysfunction-associated steatotic liver disease (MASLD). Brown seaweeds are increasingly recognized as promising marine-derived functional foods because they contain structurally unique bioactive compounds, including fucoidan, alginate, phlorotannins, and fucoxanthin. A growing body of evidence suggests that these compounds influence glucose homeostasis through multiple mechanisms, including improvement of pancreatic β-cell function, regulation of gut-mediated metabolic processes, and modulation of glucose metabolism and insulin signaling in the liver, adipose tissue, and skeletal muscle, and attenuation of chronic inflammation and oxidative stress. Brown seaweed-derived bioactive compounds have also been reported to improve abnormal lipid metabolism, a key pathological process implicated in metabolic disorders associated with T2D, including MASLD. This review provides an overview of the antidiabetic potential of brown seaweeds, with a particular focus on the mechanisms of action of their major bioactive compounds, including fucoidan, alginate, phlorotannins, and fucoxanthin.