Effects of glycemic index on plasma incretin levels

It is known that consumption of low glycemic index (GI) food inhibits the increase in plasma glucose compared to high GI food. However, the effects of low GI food on plasma incretin levels which are secreted from enteroendocrine cells of the intestines have not been studied sufficiently. Seven female university students in twenties were enrolled in the study. High GI meal and low GI meal were taken with an interval of one week or more, and blood was taken from the cubital vein before and 30, 60 and 120 min after each meal. Blood tests of low GI meal were compared with those of high GI meal. Plasma glucose at 30 and 60 min in low GI meal were significantly decreased and area under the curve (AUC) of glucose in low GI meal were significantly decreased. Plasma triglyceride at 60 and 120 min in low GI meal were significantly increased. Plasma insulin at 30 min in low GI meal was significantly decreased. Plasma gastric inhibitory polypeptide (GIP) at 30 and 60 min in low GI meal were significantly decreased and AUC of GIP in low GI meal were significantly decreased. Plasma glucagon-like peptide-1 (GLP-1) was significantly decreased only at 30 min in low GI meal. Incretins are known to augment the insulin secretory responses initiated by hyperglycemia at the pancreas. In addition, GIP stores lipid in adipose tissues which induces obesity, while GLP-1 reduces appetite, protects heart muscle and decreases blood pressure. Because low GI meal decreases plasma GIP with a little change of plasma GLP-1, the meal with low GI food may have potential benefits in the prevention or regression of obesity and cardiovascular diseases. However, the cardiovascular diseases preventive effects of low GI meal require further study because low GI meal increased plasma TG levels compared to high GI meal.