Basal insulin ameliorates post-breakfast hyperglycemia via suppression of post-breakfast proinsulin/C-peptide ratio and fasting serum free fatty acid levels in patients with type 2 diabetes

Background In general, basal insulin targets fasting plasma glucose (FPG) levels, and prandial insulin targets postprandial glucose (PPG) levels. However, the effects of basal insulin on PPG levels are controversial. We investigated the effect of basal insulin on postprandial hyperglycemia using a test meal at breakfast as well as compared differences between degludec and glargine. Methods A total of 20 participants with type 2 diabetes were randomly assigned to degludec (n = 10) or glargine (n = 10). We initiated basal-bolus insulin therapy and titrated only basal insulin until FPG was < 6.1 mmol/L. We evaluated changes in post-breakfast glucose levels and changes in clinical parameters such as serum C-peptide (CPR), proinsulin (PI), and free fatty acids (FFA) levels between the pre- and post-titration periods. Differences between degludec and glargine in the post-titration period were also evaluated. Results Post-breakfast glucose levels significantly decreased by 46.1% in the post-titration period compared with the pre-titration period (n = 20,p < 0.001). These decreases correlated positively with decreases in the post-breakfast PI/CPR ratio (r = 0.692,p < 0.001) and in fasting FFA levels (r = 0.720,p < 0.001). There were no significant differences in post-breakfast glucose levels between degludec and glargine. However, the hypoglycemic rate with degludec was significantly lower than with glargine. Conclusion Our results suggest that basal insulin with either degludec or glargine decreases the incidence of post-breakfast hyperglycemia accompanied by decreasing the post-breakfast PI/CPR ratio and fasting FFA levels in patients with type 2 diabetes.