**Abbreviations**

DM: diabetes mellitus; SGLT1: Na+/glucose cotransporter 1; OGTT: oral glucose tolerance test; AnF: fucoidan from *Ascophyllum nodosum*; KcF: fucoidan from *Kjellmaniella crassifolia*; LjF: fucoidan from *Laminaria japonica*; 2-NBDG: 2-Deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose; SPR: surface plasmon resonance; ALP: alkaline phosphatase; GLP-1: glucagon-like peptide 1; DPP-4: dipeptidyl peptidase 4; aGLP-1: active GLP-1; tGLP-1: total GLP-1; HOMA-IR: homeostasis model assessment-insulin resistance; HbA1c: hemoglobin A1c; ddH2O: double-distilled water; DMEM: Dulbecco's Modified Eagle Medium; TEER: transepithelial electrical resistance; MEM: minimum Eagle's medium; BSA: bovine serum albumin; FvF: fucoidan from *Fucus vesiculosus*, MW: molecular weight; UAs: uronic acids; DMEM: Dulbecco's Modified Eagle Medium; Metf: metformin; db/db: leptin receptor-deficient; APTT: activated partial thromboplastin time; ROS: reactive oxygen species; JNK: c-Jun N-terminal kinase; Akt: protein kinase B.
