Low glycemic index sweet potato starch improves the postprandial glycemic response of STZ/nicotinamide-induced hyperglycemic rats by upregulating the proteins involved in insulin signaling

This study was to evaluate the effects of lower-GI starch on the insulin signaling in STZ/nicotinamide-induced hyperglycemic rats. We divided 13 hyperglycemic rats and 6 normal rats randomly into two groups respectively and fed a diet containing 575 g/kg as either low-GI sweet potato starch (designed as "S") or high-GI potato starch (designed as "P"). We labeled these four groups as HG-P, HG-S (hyperglycemic rats), N-P and N-S (normal rats). After consuming the diets for 4 weeks, the skeletal muscle was collected to measure the protein expression of the insulin receptor (IR), IR substrate (IRS)-1, and glucose transporter (GLUT)4. Two intraperitoneal glucose tolerance tests (IPGTTs) were also performed at 0^th and 4^th week to evaluate the postprandial glycemic response. The results showed that the area under the curve (AUC) for blood glucose at 4^th week was significantly lower than that at 0^th week in the HG-S group. The protein expression of IRS-1 and GLUT4 in the skeletal muscle was significantly upregulated in the HG-S group compared to the HG-P group. We concluded that starch with lower-GI improved the postprandial glycemic response of hyperglycemic rats and may associate with the upregulating the proteins involved in insulin signaling.