Western blot analysis of skeletal muscle GLUT4 levels relative to β-actin revealed significant increases in all the diabetic rats supplemented with 5%, 7.5% or 15% RBBO compared to the untreated control groups (NC and NR), although there was no significant mean difference among groups. Also, no significant difference was observed between the normal control groups (569.11 ± 71.23 and 579.63 ± 66.42 pg/mL). These results indicated that diabetic rats supplemented with RBBO were unable to increase insulin concentrations to be equal to the normal groups (NC and NR). It might be that some beta cells which were damaged from STZ reagent could not completely recover. However, all diabetic rats supplemented with RBBO tended to increase insulin secretion whereas DM-MET (diabetes treated with metformin) and DMC groups showed the lowest amount of insulin concentrations (Table 2).